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Genetic Analysis and Gene Mapping of a Rice Tiller Angle Mutant tac2
Rice Science, 2009, 16(4): 323–326 Copyright © 2009, China National Rice Research Institute. Published by Elsevier BV. All rights reserved DOI: 10.1016/S1672-6308(08)60097-9
Genetic Analysis and Gene Mapping of a Rice Tiller Angle Mutant tac2 FANG Li-kui, SANG Xian-chun, YANG Zheng-lin, LIN Ying-hua, WAN Nan, HE Guang-hua (Rice Research Institute/Key Laboratory of Biotechnology and Crop Quality Improvement, Ministry of Agriculture, Southwest University, Chongqing 400716, China)
Abstract: Tiller angle, a very essential agronomic trait, is significant in rice breeding, especially in plant type breeding. A tiller angle controlling 2 (tac2) mutant was obtained from a restorer line Jinhui 10 by ethyl methane sulphonate mutagenesis. The tac2 mutant displayed normal phenotype at the seedling stage and the tiller angle significantly increased at the tillering stage. A preliminary physiological research indicated that the mutant was sensitive to GA. Thus, it is speculated that TAC2 and TAC1 might control the tiller angle in the same way. Genetic analysis showed that the mutant trait was controlled by a major recessive gene and was located on chromosome 9 using SSR markers. The genetic distances between TAC2 and its nearest markers RM3320 and RM201 were 19.2 cM and 16.7 cM, respectively. Key words: rice; tiller angle; mutant; gene mapping; genetics
Plant type is an important agronomic trait in rice, which has a great effect on photosynthetic efficiency and crop yield. Tillering capacity and tiller angle are two traits of rice plant type that influence plant architecture. An important determinant of efficient plant architecture in rice is the spatially and temporally changing of tiller angle, which affects the plant’s ability to capture light and reproduce successfully. Hence, rice tiller angle has attracted more attention recently. The heritance of rice tiller angle is very complex. Some researchers suggested that it was controlled by qualitative trait genes and others thought that it was controlled by quantitative trait loci. Research of qualitative trait gene was concentrated on tiller angle mutants such as La [1-3], La2 [4], La(t) [5], er [6], D20 [7] and Spk(t) [8]. Some quantitative trait loci have been mapped. Among them, Ta [9], qTA-9a [10], qTA-9b [10], qTA9-2 [11] and qTA-9 [12] were mapped on chromosome 9. Qualitative trait gene LAZY [13-14] and QTL gene TAC1 [15] have been cloned. Mapping, cloning and functional research of those genes which control the spread-out and compact plant architectures laid a solid foundation to reveal the genetic mechanism of plant architecture development, but the mechanism is still not clear. The mechanism of rice tiller angle development has some common features with the branch angle development of dicotyledon. Research of two Arabidopsis mutants grv2 [16] and SGR5 [17] confirmed that the mutation in the key gene related to the receipt and conduction of gravitation signal resulted in weakening or even loss of the agravitropism of Arabidopsis lateral branch. The rice la mutant has been intensively studied for decades. Physiological experiments showed that the spread phenotype before tillering was positively correlated to the
agravitropism loss at the seedling stage. These indicate that the gravity signal is an important factor determining plant branching or tillering and affects plants throughout the whole rice growth period. A novel tac2 mutant was selected from a restorer rice line Jinhui 10 treated by ethyl methane sulphonate (EMS) in our laboratory. Compared with original parent, the mutant showed normal phenotype at the seedling stage and spread before tillering. It was then temporarily named as tac2 (tiller angle control 2). This paper reports its physiological characters and genetic mapping.
Received: 2 June 2009; Accepted: 29 August 2009 Corresponding author: HE Guang-hua ([email protected]) This is an English version of the paper published in Chinese in Chinese Journal of Rice Science, Vol. 23, No. 3, 2009, Pages 315–318.
The tac2 mutant was treated with the solution of 1.0 and 0.1 mg/L GA at the tillering stage. The plant height and the length of uppermost leaf were recorded after 10 days of
MATERIALS AND METHODS Plant materials A rice tac2 mutant was selected from a restorer rice line Jinhui 10 treated by EMS. The characters were stabilized after five generations of self-crossing in Beibei, Chongqing and Lingshui, Hainan, China. Experimental methods Measuring of tiller angle and plant-type In order to compare the plant type between the wild type and the mutant, the widths (W) of the cross-sections at the same height (H) of the wild type and the mutant were measured (Fig. 1), and the ratio of W to H was used as an index to reflect tiller angle. Gibberellic acid (GA) treatments
Rice Science, Vol. 16, No. 4, 2009
324 treatments. The tac2 mutant treated with water was as a control. The significant difference analysis was conducted.
by electrophoresis on 10.0% polyacrylamide gels, and the band patterns were visualized using a silver staining protocol [22].
Genetic analysis In the summer of 2003, the tac2 mutant, as a paternal parent, was crossed with Xinong 1A at the experimental farm in Beibei, Chongqing, China. In the spring of 2007, the F1 was planted in Hainan Province, China, and in the summer of 2007, a large F2 population of tac2 mutant was planted at the experimental farm in Beibei, Chongqing, China. The genetic analysis of plant-type was conducted at the booting stage. DNA extraction The DNAs of parents were extracted using the CTAB method, and the DNAs of individual plants of F2 population were extracted using the alkali-treated method [20-21]. SSR marker analysis The primer sequences of SSR markers were downloaded from http://www.gramene.org/ and the primers were synthesized by the Shanghai Sangon Inc, China. PCR amplification was performed in a 25 μL reaction system containing 2.5 μL of 10×PCR bufferˈ1.3 μL of 25 mmol/L MgCl2, 1.0 μL of 2.5 mmol/L dNTPs, 16.0 μL of ddH2O, 2.0 μL of 10 μmol/L primers, 2.0 μL of DNA, 0.2 μL of Taq DNA polymerase (5 U/μL). DNA amplification was performed with a PCR machine, programmed for 1 min at 94°C, then followed by 35 cycles of 30 s at 94°C, 30 s at 55°C, and 1 min at 72°C, succeeded by 10 min at 72°C for final extension. PCR products were separated
Fig. 1. Phenotypes of the mutant tac2 and its wild type. A, B and C, At the tillering stage; D, At the heading stage.
RESULTS Phenotype of the tac2 mutant At the seedling stage, the tact2 mutant displayed normal phenotype, and the tiller angle significantly increased compared with the wild type at the tillering stage (Fig. 1). The widest cross-sections at the 10-cm height from the ground of 10 plants from the mutant and the wild type were measured, respectively. The average W/H ratio between the mutant (0.68) and the wild type (0.39) showed a significant difference. At the same growth stage, the tac2 mutant was shorter than the wild type, indicating that the TAC2 gene may have pleiotropy. GA-sensitivity test According to the response to exogenous GA, dwarf mutants could be divided into GA defective and GA insensitive types. In the GA defective mutants, the GA biosynthetic pathway is inhibited or blocked, resulting in endogenous GA absence or trace existence, so application of exogenous GA on dwarf mutants would make them restore to wild-type phenotypes [23]. Compared with the wild type, the plant height of tac2 was significantly reduced. However, when the tac2 mutant was treated with 1.0 and 0.1 mg/L GA, the plant height and the leaf length were significant increased, but the tiller angle showed no significant difference
FANG Li-kui, et al. Genetic Analysis and Gene Mapping of a Rice Tiller Angle Mutant tac2
325
Fig. 2. SSR patterns amplified with RM1026 in individuals of F2 segregation population for verification. P1, Xinong 1A; P2, tac2; Lanes 1 to 10, Individuals of population with wild type characters selected from F2; Lanes 11 to 20, Individuals of population with spread-out plant characters selected from F2. Table 1. GA sensitive examination of the tac2 mutant.
GA level (mg/L) 1.0 0.1 0.0 (CK)
Plant height (cm) 93.8 A 76.6 B 61.2 C
Leaf length (cm) 51.2 A 40.2 B 38.6 B
Width of cross-section/Height 0.40 a 0.43 a 0.42 a
Within a column, values followed by the same uppercase and lowercase letters are not significantly different at the 0.01 and 0.05 levels, respectively.
between the treatments and the control, indicating that the tac2 mutant was sensitive to GA (Table 1). Genetic analysis When tac2 was crossed with Xinong 1A, its F1 displayed normal phenotype. There were two phenotypes in F2 population, the wild type and the mutant type. The number of wild type plants was 475 and that of the mutant type plants was 150, which fitted a ratio of 3:1 by the ••2 test (••2=0.33<3.84). This indicates that the characters were controlled by a single recessive nuclear gene. Identification of the tac2 locus The polymorphism between the tac2 mutant and Xinong 1A was assessed with 400 SSR markers, and 90 of which were polymorphic. The PCRs were conducted with the DNAs from two parents, mutant bulk and normal bulk with the polymorphic SSR markers. The results showed that RM201 and RM1026 markers on chromosome 9 were co-segregated with the tac2 locus (Fig. 2). The chromosomal location of tac2 was determined by observing the genotypes of 150 tac2 mutants, and the tac2 locus was then primarily mapped on chromosome 9, with the genetic distances of 16.7 cM and 32.0 cM to RM201 and RM1026, respectively. In order to map the target gene at a smaller interval, five new SSR markers on the other side of RM201 and RM3320 were designed. The polymorphism was found between tac2 and Xinong 1A on RM3320. The genetic distance was 19.2 cM between the target gene and RM3320. The tac2 locus was then mapped between RM3320 and RM201/RM1026 (Fig. 3).
Fig. 3. Mapping of the tac2 locus on chromosome 9.
some quantitative trait loci (QTL) affecting tiller angle in rice have been identified by several research groups. However, TAC1 [15] is the only cloned QTL, which belongs to a new gene family especially in members of the Graminae. The 3ƍ-UTR of TAC1 and the unidentified factor(s) regulate the expression of TAC1, and the level of tac1 mRNA controls the development of tiller angle. We mapped the TAC2 gene on chromosome 9 between the SSR markers RM3320 and RM201, which was not allelic with TAC1, although the phenotype of tac2 mutant was similar with that of the TAC1, indicating that the TAC2 might be a novel gene related to the development of tiller angle. The LAZY1 [13-14] and OsPIN1 genes regulate the rice endogenous auxin polarity transport. The tiller angle of OsPIN1 RNAi transgenic plants is significantly larger than its wild type. In addition, auxin can promote apical dominance and inhibit lateral bud growth. The tac2 mutant was sensitive to GA, and the exogenous GA could significantly increase the elongation of internodes, but had no effect on the development of tiller angle. The tac2 mutant had normal phenotype at the seedling stage, which is different from the lazy1 mutant. Hence, we speculate that TAC2 affects the auxin distribution in other way. According to our findings and previous research, we speculate that there are two interaction ways in rice controlling the tiller angle development. One is a gravity signaling pathway which affects the plant architectures throughout the growth period. If the key gene in this signaling way mutated, the mutant will display a lazy phenotype at the seedling stage, just like the la(t) mutant. The other way is dependent on the plant development, and the gene expression has temporal and spatial specificity during plant development, such as TCA1. TAC1 and TAC2 may belong to the same way, but it remains to be further supported from the TAC2 cloning and functional research.
DISCUSSION
ACKNOWLEDGEMENTS
Several genetic loci that control tiller angle in rice have been identified using both classical and molecular methods and
This work was supported by the Doctoral Fund of Ministry of Education of China (Grant No. 20070635005), Ministry of
Rice Science, Vol. 16, No. 4, 2009
326 Major Science & Technology of Chongqing, China (Grant No. CSTC2007AA1019).
Chinese with English abstract) 13 Li P J, Wang Y H, Qian Q, Fu Z M, Wang M, Zeng D L, Li B H, Wang X J, Li J Y. LAZY1 controls rice shoot gravitropism through regulating polar auxin transport. Cell Res, 2007, 17:
REFERENCES 1
Takahashi M. Linkage groups and gene schemes of some
402–410. 14 Yoshihara T, Iino M. Identification of the gravitropism-related rice gene LAZY1 and elucidation of LAZY1-dependent and
striking morphological characters in Japanese rice. In: IRRI.
-independent gravity signaling pathways. Plant Cell Physiol,
Rice Genetics and Cytogenetics. Amsterdam: Elsevier, 1964: 215–236. 2
Kishimoto N, Foolad M R, Shimosaka E, Matsuura S, Saito A.
2007, 48(5): 678–688. 15 Yu B, Lin Z, Li H, Li X, Li J, Wang Y, Zhang X, Zhu Z, Zhai W, Wang X, Xie D, Sun C. TAC1, a major quantitative trait
Alignment of molecular and classical linkage maps of rice.
locus controlling tiller angle in rice. Plant J, 2007, 52(5):
Plant Cell Rep, 1993, 12: 457–461. 3
Singh K, Multani D S, Khush G S. Secondary trisomic and telotrisomics of rice: Origin, characterization, and use in
891–898. 16
determining the orientation of chromosome map. Genetics,
Arabidopsis are deficient in a protein implicated in
1996, 143: 517–529. 4
endocytosis in Caenorhabditis elegans. Plant Physiol, 2004,
Li P J, Zeng D L, Liu X F, Xu D, Gu D, Li J Y, Qian Q. Mapping and characterization of a tiller-spreading mutant lazy-2 in rice. Chinese Sci Bull, 2003, 48(24): 2271–2274. (in
136(2): 3095–3103. 17
SGR5, is involved in early events of gravitropism in
Zhang H Y, Yang F, Li Y, Xu P Z, Wang X D, Wu X J.
Arabidopsis inflorescence stems. Plant J, 2006, 47(4): 619–
Identification and gene mapping of a gravitropism mutant in rice. Chinese Agric Sci Bull, 2006, 33(2): 142–146. (in Chinese with English abstract) 6
628. 18 Abe K, Takahashi H, Suge H. Lazy gene (la) responsible for both an agravitropism of seedlings and lazy habit of tiller
Takahashi M, Kinoshita T, Takeda K. Character expression
growth in rice (Oryza sativa L.). Plant Res, 1996, 109(1096):
and caudal genes of some mutants in rice. Fac Agric Hokkaido Univ, 1968, 54: 496–512. 7
Kinoshita T, Takahashi M, Mori K. Character expression and
381–386. 19 Yoshihara T, Iino M. Circumnutation of rice coleoptiles: Its relationships with gravitropism and absence in lazy mutants.
inheritance node of three kinds of dwarf rice. Res Bull Farm Hokkaido Univ, 1974, 19: 64–75. 8
Maiyata M, Komori T, Yamamoto T, Ueda T, Yano M, Nitta N. Fine scale and physical mapping of Spk(t) controlling spreading stub in rice. Breeding Sci, 2005, 55: 237–239.
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tiller angle in rice. J Genet Gen, 2001, 28(1): 29–32. (in 11 Shen S Q, Zhuang J Y, Bao J S, Zheng K L, Xia Y W, Shu Q Y. Analysis of QTLs with additive, epistasis and G×E interaction effects of the tillering angle trait in rice. J Agric Biotech, 2005, 13(1): 16–20. (in Chinese with English abstract) 12 Yu C Y, Liu Y Q, Jiang L, Wang C M, Zhai H Q, Wang J M. QTLs mapping and genetic analysis of tiller angle in rice (Oryza sativa L.). J Genet Gen, 2005, 32(9): 948–954. (in
Sang X C, He G H, Zhang Y, Yang Z L, Pei Y. The simple gain of templates of rice genomes DNA for PCR. Genetics,
10 Qian Q, He P, Teng S, Zeng D L, Zhu L H. QTLs analysis of Chinese with English abstract)
Rogers S O, Bendich A J. Extraction of DNA from plant tissues. Plant Mol Biol Manual, 1998, A6: 1–10.
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Li Z, Paterson A H, Pinson S R M, Stansel J W. RFLP facilitated analysis of tiller and leaf angles in rice (Oryza
Morita M T, Sakaguchi K, Kiyose S, Taira K, Kato T, Nakamura M, Tasaka M. A C2H2-type zinc finger protein,
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Silady R A, Kato T, Lukowitz W, Sieber P, Tasaka M, Somerville C R. The gravitropism defective 2 mutants of
Genet, 1996, 252: 597–607. 23
Wang Y H, Han L B, Zeng H M, Yi S X, Qing L. The development of dwarf mutants related gibberellin. China Biotech, 2006, 26(8): 22–27. (in Chinese with English abstract)
24 Xu M, Zhu L, Shou H X, Wu P. A PIN1 family gene, OsPIN1, involved in auxin-dependent adventitious root emergence and tillering in rice. Plant Cell Physiol, 2005, 46(10): 1674–1681.
Genetic Analysis and Gene Mapping of a Rice Tiller Angle Mutant tac2 FANG Li-kui, SANG Xian-chun, YANG Zheng-lin, LIN Ying-hua, WAN Nan, HE Guang-hua (Rice Research Institute/Key Laboratory of Biotechnology and Crop Quality Improvement, Ministry of Agriculture, Southwest University, Chongqing 400716, China)
Abstract: Tiller angle, a very essential agronomic trait, is significant in rice breeding, especially in plant type breeding. A tiller angle controlling 2 (tac2) mutant was obtained from a restorer line Jinhui 10 by ethyl methane sulphonate mutagenesis. The tac2 mutant displayed normal phenotype at the seedling stage and the tiller angle significantly increased at the tillering stage. A preliminary physiological research indicated that the mutant was sensitive to GA. Thus, it is speculated that TAC2 and TAC1 might control the tiller angle in the same way. Genetic analysis showed that the mutant trait was controlled by a major recessive gene and was located on chromosome 9 using SSR markers. The genetic distances between TAC2 and its nearest markers RM3320 and RM201 were 19.2 cM and 16.7 cM, respectively. Key words: rice; tiller angle; mutant; gene mapping; genetics
Plant type is an important agronomic trait in rice, which has a great effect on photosynthetic efficiency and crop yield. Tillering capacity and tiller angle are two traits of rice plant type that influence plant architecture. An important determinant of efficient plant architecture in rice is the spatially and temporally changing of tiller angle, which affects the plant’s ability to capture light and reproduce successfully. Hence, rice tiller angle has attracted more attention recently. The heritance of rice tiller angle is very complex. Some researchers suggested that it was controlled by qualitative trait genes and others thought that it was controlled by quantitative trait loci. Research of qualitative trait gene was concentrated on tiller angle mutants such as La [1-3], La2 [4], La(t) [5], er [6], D20 [7] and Spk(t) [8]. Some quantitative trait loci have been mapped. Among them, Ta [9], qTA-9a [10], qTA-9b [10], qTA9-2 [11] and qTA-9 [12] were mapped on chromosome 9. Qualitative trait gene LAZY [13-14] and QTL gene TAC1 [15] have been cloned. Mapping, cloning and functional research of those genes which control the spread-out and compact plant architectures laid a solid foundation to reveal the genetic mechanism of plant architecture development, but the mechanism is still not clear. The mechanism of rice tiller angle development has some common features with the branch angle development of dicotyledon. Research of two Arabidopsis mutants grv2 [16] and SGR5 [17] confirmed that the mutation in the key gene related to the receipt and conduction of gravitation signal resulted in weakening or even loss of the agravitropism of Arabidopsis lateral branch. The rice la mutant has been intensively studied for decades. Physiological experiments showed that the spread phenotype before tillering was positively correlated to the
agravitropism loss at the seedling stage. These indicate that the gravity signal is an important factor determining plant branching or tillering and affects plants throughout the whole rice growth period. A novel tac2 mutant was selected from a restorer rice line Jinhui 10 treated by ethyl methane sulphonate (EMS) in our laboratory. Compared with original parent, the mutant showed normal phenotype at the seedling stage and spread before tillering. It was then temporarily named as tac2 (tiller angle control 2). This paper reports its physiological characters and genetic mapping.
Received: 2 June 2009; Accepted: 29 August 2009 Corresponding author: HE Guang-hua ([email protected]) This is an English version of the paper published in Chinese in Chinese Journal of Rice Science, Vol. 23, No. 3, 2009, Pages 315–318.
The tac2 mutant was treated with the solution of 1.0 and 0.1 mg/L GA at the tillering stage. The plant height and the length of uppermost leaf were recorded after 10 days of
MATERIALS AND METHODS Plant materials A rice tac2 mutant was selected from a restorer rice line Jinhui 10 treated by EMS. The characters were stabilized after five generations of self-crossing in Beibei, Chongqing and Lingshui, Hainan, China. Experimental methods Measuring of tiller angle and plant-type In order to compare the plant type between the wild type and the mutant, the widths (W) of the cross-sections at the same height (H) of the wild type and the mutant were measured (Fig. 1), and the ratio of W to H was used as an index to reflect tiller angle. Gibberellic acid (GA) treatments
Rice Science, Vol. 16, No. 4, 2009
324 treatments. The tac2 mutant treated with water was as a control. The significant difference analysis was conducted.
by electrophoresis on 10.0% polyacrylamide gels, and the band patterns were visualized using a silver staining protocol [22].
Genetic analysis In the summer of 2003, the tac2 mutant, as a paternal parent, was crossed with Xinong 1A at the experimental farm in Beibei, Chongqing, China. In the spring of 2007, the F1 was planted in Hainan Province, China, and in the summer of 2007, a large F2 population of tac2 mutant was planted at the experimental farm in Beibei, Chongqing, China. The genetic analysis of plant-type was conducted at the booting stage. DNA extraction The DNAs of parents were extracted using the CTAB method, and the DNAs of individual plants of F2 population were extracted using the alkali-treated method [20-21]. SSR marker analysis The primer sequences of SSR markers were downloaded from http://www.gramene.org/ and the primers were synthesized by the Shanghai Sangon Inc, China. PCR amplification was performed in a 25 μL reaction system containing 2.5 μL of 10×PCR bufferˈ1.3 μL of 25 mmol/L MgCl2, 1.0 μL of 2.5 mmol/L dNTPs, 16.0 μL of ddH2O, 2.0 μL of 10 μmol/L primers, 2.0 μL of DNA, 0.2 μL of Taq DNA polymerase (5 U/μL). DNA amplification was performed with a PCR machine, programmed for 1 min at 94°C, then followed by 35 cycles of 30 s at 94°C, 30 s at 55°C, and 1 min at 72°C, succeeded by 10 min at 72°C for final extension. PCR products were separated
Fig. 1. Phenotypes of the mutant tac2 and its wild type. A, B and C, At the tillering stage; D, At the heading stage.
RESULTS Phenotype of the tac2 mutant At the seedling stage, the tact2 mutant displayed normal phenotype, and the tiller angle significantly increased compared with the wild type at the tillering stage (Fig. 1). The widest cross-sections at the 10-cm height from the ground of 10 plants from the mutant and the wild type were measured, respectively. The average W/H ratio between the mutant (0.68) and the wild type (0.39) showed a significant difference. At the same growth stage, the tac2 mutant was shorter than the wild type, indicating that the TAC2 gene may have pleiotropy. GA-sensitivity test According to the response to exogenous GA, dwarf mutants could be divided into GA defective and GA insensitive types. In the GA defective mutants, the GA biosynthetic pathway is inhibited or blocked, resulting in endogenous GA absence or trace existence, so application of exogenous GA on dwarf mutants would make them restore to wild-type phenotypes [23]. Compared with the wild type, the plant height of tac2 was significantly reduced. However, when the tac2 mutant was treated with 1.0 and 0.1 mg/L GA, the plant height and the leaf length were significant increased, but the tiller angle showed no significant difference
FANG Li-kui, et al. Genetic Analysis and Gene Mapping of a Rice Tiller Angle Mutant tac2
325
Fig. 2. SSR patterns amplified with RM1026 in individuals of F2 segregation population for verification. P1, Xinong 1A; P2, tac2; Lanes 1 to 10, Individuals of population with wild type characters selected from F2; Lanes 11 to 20, Individuals of population with spread-out plant characters selected from F2. Table 1. GA sensitive examination of the tac2 mutant.
GA level (mg/L) 1.0 0.1 0.0 (CK)
Plant height (cm) 93.8 A 76.6 B 61.2 C
Leaf length (cm) 51.2 A 40.2 B 38.6 B
Width of cross-section/Height 0.40 a 0.43 a 0.42 a
Within a column, values followed by the same uppercase and lowercase letters are not significantly different at the 0.01 and 0.05 levels, respectively.
between the treatments and the control, indicating that the tac2 mutant was sensitive to GA (Table 1). Genetic analysis When tac2 was crossed with Xinong 1A, its F1 displayed normal phenotype. There were two phenotypes in F2 population, the wild type and the mutant type. The number of wild type plants was 475 and that of the mutant type plants was 150, which fitted a ratio of 3:1 by the ••2 test (••2=0.33<3.84). This indicates that the characters were controlled by a single recessive nuclear gene. Identification of the tac2 locus The polymorphism between the tac2 mutant and Xinong 1A was assessed with 400 SSR markers, and 90 of which were polymorphic. The PCRs were conducted with the DNAs from two parents, mutant bulk and normal bulk with the polymorphic SSR markers. The results showed that RM201 and RM1026 markers on chromosome 9 were co-segregated with the tac2 locus (Fig. 2). The chromosomal location of tac2 was determined by observing the genotypes of 150 tac2 mutants, and the tac2 locus was then primarily mapped on chromosome 9, with the genetic distances of 16.7 cM and 32.0 cM to RM201 and RM1026, respectively. In order to map the target gene at a smaller interval, five new SSR markers on the other side of RM201 and RM3320 were designed. The polymorphism was found between tac2 and Xinong 1A on RM3320. The genetic distance was 19.2 cM between the target gene and RM3320. The tac2 locus was then mapped between RM3320 and RM201/RM1026 (Fig. 3).
Fig. 3. Mapping of the tac2 locus on chromosome 9.
some quantitative trait loci (QTL) affecting tiller angle in rice have been identified by several research groups. However, TAC1 [15] is the only cloned QTL, which belongs to a new gene family especially in members of the Graminae. The 3ƍ-UTR of TAC1 and the unidentified factor(s) regulate the expression of TAC1, and the level of tac1 mRNA controls the development of tiller angle. We mapped the TAC2 gene on chromosome 9 between the SSR markers RM3320 and RM201, which was not allelic with TAC1, although the phenotype of tac2 mutant was similar with that of the TAC1, indicating that the TAC2 might be a novel gene related to the development of tiller angle. The LAZY1 [13-14] and OsPIN1 genes regulate the rice endogenous auxin polarity transport. The tiller angle of OsPIN1 RNAi transgenic plants is significantly larger than its wild type. In addition, auxin can promote apical dominance and inhibit lateral bud growth. The tac2 mutant was sensitive to GA, and the exogenous GA could significantly increase the elongation of internodes, but had no effect on the development of tiller angle. The tac2 mutant had normal phenotype at the seedling stage, which is different from the lazy1 mutant. Hence, we speculate that TAC2 affects the auxin distribution in other way. According to our findings and previous research, we speculate that there are two interaction ways in rice controlling the tiller angle development. One is a gravity signaling pathway which affects the plant architectures throughout the growth period. If the key gene in this signaling way mutated, the mutant will display a lazy phenotype at the seedling stage, just like the la(t) mutant. The other way is dependent on the plant development, and the gene expression has temporal and spatial specificity during plant development, such as TCA1. TAC1 and TAC2 may belong to the same way, but it remains to be further supported from the TAC2 cloning and functional research.
DISCUSSION
ACKNOWLEDGEMENTS
Several genetic loci that control tiller angle in rice have been identified using both classical and molecular methods and
This work was supported by the Doctoral Fund of Ministry of Education of China (Grant No. 20070635005), Ministry of
Rice Science, Vol. 16, No. 4, 2009
326 Major Science & Technology of Chongqing, China (Grant No. CSTC2007AA1019).
Chinese with English abstract) 13 Li P J, Wang Y H, Qian Q, Fu Z M, Wang M, Zeng D L, Li B H, Wang X J, Li J Y. LAZY1 controls rice shoot gravitropism through regulating polar auxin transport. Cell Res, 2007, 17:
REFERENCES 1
Takahashi M. Linkage groups and gene schemes of some
402–410. 14 Yoshihara T, Iino M. Identification of the gravitropism-related rice gene LAZY1 and elucidation of LAZY1-dependent and
striking morphological characters in Japanese rice. In: IRRI.
-independent gravity signaling pathways. Plant Cell Physiol,
Rice Genetics and Cytogenetics. Amsterdam: Elsevier, 1964: 215–236. 2
Kishimoto N, Foolad M R, Shimosaka E, Matsuura S, Saito A.
2007, 48(5): 678–688. 15 Yu B, Lin Z, Li H, Li X, Li J, Wang Y, Zhang X, Zhu Z, Zhai W, Wang X, Xie D, Sun C. TAC1, a major quantitative trait
Alignment of molecular and classical linkage maps of rice.
locus controlling tiller angle in rice. Plant J, 2007, 52(5):
Plant Cell Rep, 1993, 12: 457–461. 3
Singh K, Multani D S, Khush G S. Secondary trisomic and telotrisomics of rice: Origin, characterization, and use in
891–898. 16
determining the orientation of chromosome map. Genetics,
Arabidopsis are deficient in a protein implicated in
1996, 143: 517–529. 4
endocytosis in Caenorhabditis elegans. Plant Physiol, 2004,
Li P J, Zeng D L, Liu X F, Xu D, Gu D, Li J Y, Qian Q. Mapping and characterization of a tiller-spreading mutant lazy-2 in rice. Chinese Sci Bull, 2003, 48(24): 2271–2274. (in
136(2): 3095–3103. 17
SGR5, is involved in early events of gravitropism in
Zhang H Y, Yang F, Li Y, Xu P Z, Wang X D, Wu X J.
Arabidopsis inflorescence stems. Plant J, 2006, 47(4): 619–
Identification and gene mapping of a gravitropism mutant in rice. Chinese Agric Sci Bull, 2006, 33(2): 142–146. (in Chinese with English abstract) 6
628. 18 Abe K, Takahashi H, Suge H. Lazy gene (la) responsible for both an agravitropism of seedlings and lazy habit of tiller
Takahashi M, Kinoshita T, Takeda K. Character expression
growth in rice (Oryza sativa L.). Plant Res, 1996, 109(1096):
and caudal genes of some mutants in rice. Fac Agric Hokkaido Univ, 1968, 54: 496–512. 7
Kinoshita T, Takahashi M, Mori K. Character expression and
381–386. 19 Yoshihara T, Iino M. Circumnutation of rice coleoptiles: Its relationships with gravitropism and absence in lazy mutants.
inheritance node of three kinds of dwarf rice. Res Bull Farm Hokkaido Univ, 1974, 19: 64–75. 8
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