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Mutations in the gene encoding starch synthase II profoundly alter amylopectin structure in pea embryos
190
Paper alert
Controlled cytokinin production in transgenic tobacco using a copper-inducible promoter. McKenzie Ml, Mett V, Reynolds PHS, Jameson PE: Plant Physiol 1998, 116:969-977. ?? Significance: These results extend the value of a copper inducible promoter as a means of controlling the expression of transgenes in plants, Findings: The native promoter from a cytokinin synthase gene (ipt) from Agrobacterium tumefaciens was replaced by a copper-inducible promoter and was introduced into tobacco plants. Under normal conditions all plants were morphologically normal, but in vitro application of 50mM copper sulphate resulted in delayed senescence and an increase in cytokinin concentration.
Physiology and metabolism Selected by Steven Hill and Lee Sweetlove University of Oxford, Oxford, UK
The role of UDP-glucose epimerase in carbohydrate metabDormann P, Benning C: Plant J 1998, olism of Arabidopsis. 13:641-652. ??Significance: Interactions between galactose metabolism and leaf carbohydrate metabolism in general are described, and a potential for use of UDP-glucose epimerase as a selectable marker suggested. Findings: Transgenic Arabidopsis have been produced with reduced and elevated activities of UDP-glucose epimerase, the enzyme responsible for the interconversion of UDP-glucose and UDP-galactose. These manipulations appear to have little effect when the plants are grown in the absence of galactose, but in the presence of galactose growth of the antisense lines is severely reduced, while the over-expressers are more tolerant of galactose than the wild-type. The wild-type also accumulates large amounts of starch in the presence of galactose, while the high UDP-glucose epimerase lines are unaffected. These results suggest that galactose toxicity in plants results from limitations in the conversion of UDP-galactose to UDP-glucose. Characterization of dulll, a maize gene coding for a novel starch synthase. Gao M, Wanat J, Stinard PS, James MG, Myers AM: Plant Cell 1998, 10:399-412. AND Mutations in the gene encoding starch synthase II profoundly alter amylopectin structure in pea embryos. Craig J, Lloyd JR, Tomlinson K, Barber L, Edwards A, Wang TL, Martin C, Hedley CL, Smith AM: P/ant Cell 1998, lo:41 3-426. ?? * Significance: A role for starch synthase II in the synthesis of long chain glucans in amylopectin is established. Findings: The dull7 gene of maize has been cloned and identified as coding for starch synthase II (SSII), while the rug5 locus of pea contains the coding region of SSII. Detailed investigation
of amylopectin structure in rug5 plants suggests for the extension of short chain glucans
that SSII is responsible during
amylopectin
a higher
abundance
synthesis; of very
in the short
mutant:plants
chain
lengths
there within
is the
amylopectin. These properties are similar to those previously described for amylopectin from dull7 plants, suggesting that the synthesis general
of long glucan
chains
within
amylopectin
may be a
role for SSII.
Chimeric Arabidopsis fhaliana ribulose-1,5-bisphosphate carboxylase/oxygenase containing a pea small subunit protein is compromised in carbamylation. Getzoff TP, Zhu G, Bohnert HJ, Jenson RG: Plant Physiology 1998, 116:695-702.
??Significance: A potential regulatory role for the small subunit of Rubisco is proposed. Findings: A cDNA encoding the pea Rubisco small subunit was expressed in transgenic Arabidopsis plants. The pea subunit was stabley incorporated into the Arabidopsis Rubisco, with 1 pea subunit occurring in each holoenzyme complex. The chimeric complex has reduced activity compared to the wild-type Arabidopsis complex, and this can largely be explained by reduced carbamylation of the active site; only 7 out of the 8 large subunits are carbamylated. This suggest that the small subunit has a role in activation of Rubsico through carbamylation.
Effects of genetic modifications of nitrate reductase expression on 1sNOs uptake and reduction in Nicotiana plants. Gojon A, Dapoigny L, Lejay L, Tillard P, Rufty TW: Plant, Cell and Environment 1998, 21:43-53. ?? Significance: The role of nitrate reductase in the control of nitrate uptake and metabolism is investigated, and the existence of a mechanism for the feedback regulation of nitrate uptake suggested. Findings: The rate of uptake and metabolism of 15NOs in transgenic Nicotiana with elevated or reduced nitrate reductase activity was investigated. The rate of nitrate reduction was dependent on the nitrate reductase activity, suggesting that the enzyme exerts significant control on this flux. In the high activity lines, however, total nitrogen assimilation was not increased, despite an increase in the rate of nitrate reduction. This was because of a reduction in nitrate uptake, which suggests feedback regulation of uptake. Trehalose-6-phosphate phosphatases from Arabidopsis thaliana: identification by functional complementation of the yeast tsp2 mutant Vogel G, Aeschbacher RA, Mtiller J, Boller T, Wiemken A: Plant Journal 1998, 13:673-683. ?? Significance: Trehalose plays an important role in the desiccation
tolerance
of many organisms,
but is believed
to be
absent from plants. This paper, however, reports the cloning of a cDNA encoding one of the enzymes of trehalose biosynthesis from Arabidopsis.
Findings: Two Arabidopsis cDNAs were isolated on the basis of their ability to complement the yeast mutant tps2 which is deficient in trehalose-6-phosphate phosphatase. This enzyme is essential show
for the synthesis
significant
phosphatases
homology
of trehalose. to
other
The
plant
cDNAs
trehalose-6-phosphate
and lead to the synthesis
of trehalose
both
in
vivo and in vitro in fps2 yeast. This suggests that the trehalose biosynthetic pathway is present in Arabidopsis.
Plant-microbe
interactions
Selected by Edward Farmer University of Lausanne, Lausanne, Switzerland
Ethylene-insensitive tobacco lacks nonhost resistance against soil-borne fungi. Knoester M, van Loon LC, van den Heuvel J, Hennig J, Bol JF, Linthorst HJM: Proc Nat/ Acad Sci USA 1998, 95:i 933-l 937. ?? * Significance: This elegant paper shows the importance of ethylene perception in non-host resistance to soil-borne fungi. The authors stress that the role of ethylene perception in disease resistance depends on the pathogen (see the following alert concerning ethylene and virulent pathogens). The impaired social signalling in transgenic plants will provide the basis of many informative own right.
experiments
and
is a major
finding
in its
Paper alert
Controlled cytokinin production in transgenic tobacco using a copper-inducible promoter. McKenzie Ml, Mett V, Reynolds PHS, Jameson PE: Plant Physiol 1998, 116:969-977. ?? Significance: These results extend the value of a copper inducible promoter as a means of controlling the expression of transgenes in plants, Findings: The native promoter from a cytokinin synthase gene (ipt) from Agrobacterium tumefaciens was replaced by a copper-inducible promoter and was introduced into tobacco plants. Under normal conditions all plants were morphologically normal, but in vitro application of 50mM copper sulphate resulted in delayed senescence and an increase in cytokinin concentration.
Physiology and metabolism Selected by Steven Hill and Lee Sweetlove University of Oxford, Oxford, UK
The role of UDP-glucose epimerase in carbohydrate metabDormann P, Benning C: Plant J 1998, olism of Arabidopsis. 13:641-652. ??Significance: Interactions between galactose metabolism and leaf carbohydrate metabolism in general are described, and a potential for use of UDP-glucose epimerase as a selectable marker suggested. Findings: Transgenic Arabidopsis have been produced with reduced and elevated activities of UDP-glucose epimerase, the enzyme responsible for the interconversion of UDP-glucose and UDP-galactose. These manipulations appear to have little effect when the plants are grown in the absence of galactose, but in the presence of galactose growth of the antisense lines is severely reduced, while the over-expressers are more tolerant of galactose than the wild-type. The wild-type also accumulates large amounts of starch in the presence of galactose, while the high UDP-glucose epimerase lines are unaffected. These results suggest that galactose toxicity in plants results from limitations in the conversion of UDP-galactose to UDP-glucose. Characterization of dulll, a maize gene coding for a novel starch synthase. Gao M, Wanat J, Stinard PS, James MG, Myers AM: Plant Cell 1998, 10:399-412. AND Mutations in the gene encoding starch synthase II profoundly alter amylopectin structure in pea embryos. Craig J, Lloyd JR, Tomlinson K, Barber L, Edwards A, Wang TL, Martin C, Hedley CL, Smith AM: P/ant Cell 1998, lo:41 3-426. ?? * Significance: A role for starch synthase II in the synthesis of long chain glucans in amylopectin is established. Findings: The dull7 gene of maize has been cloned and identified as coding for starch synthase II (SSII), while the rug5 locus of pea contains the coding region of SSII. Detailed investigation
of amylopectin structure in rug5 plants suggests for the extension of short chain glucans
that SSII is responsible during
amylopectin
a higher
abundance
synthesis; of very
in the short
mutant:plants
chain
lengths
there within
is the
amylopectin. These properties are similar to those previously described for amylopectin from dull7 plants, suggesting that the synthesis general
of long glucan
chains
within
amylopectin
may be a
role for SSII.
Chimeric Arabidopsis fhaliana ribulose-1,5-bisphosphate carboxylase/oxygenase containing a pea small subunit protein is compromised in carbamylation. Getzoff TP, Zhu G, Bohnert HJ, Jenson RG: Plant Physiology 1998, 116:695-702.
??Significance: A potential regulatory role for the small subunit of Rubisco is proposed. Findings: A cDNA encoding the pea Rubisco small subunit was expressed in transgenic Arabidopsis plants. The pea subunit was stabley incorporated into the Arabidopsis Rubisco, with 1 pea subunit occurring in each holoenzyme complex. The chimeric complex has reduced activity compared to the wild-type Arabidopsis complex, and this can largely be explained by reduced carbamylation of the active site; only 7 out of the 8 large subunits are carbamylated. This suggest that the small subunit has a role in activation of Rubsico through carbamylation.
Effects of genetic modifications of nitrate reductase expression on 1sNOs uptake and reduction in Nicotiana plants. Gojon A, Dapoigny L, Lejay L, Tillard P, Rufty TW: Plant, Cell and Environment 1998, 21:43-53. ?? Significance: The role of nitrate reductase in the control of nitrate uptake and metabolism is investigated, and the existence of a mechanism for the feedback regulation of nitrate uptake suggested. Findings: The rate of uptake and metabolism of 15NOs in transgenic Nicotiana with elevated or reduced nitrate reductase activity was investigated. The rate of nitrate reduction was dependent on the nitrate reductase activity, suggesting that the enzyme exerts significant control on this flux. In the high activity lines, however, total nitrogen assimilation was not increased, despite an increase in the rate of nitrate reduction. This was because of a reduction in nitrate uptake, which suggests feedback regulation of uptake. Trehalose-6-phosphate phosphatases from Arabidopsis thaliana: identification by functional complementation of the yeast tsp2 mutant Vogel G, Aeschbacher RA, Mtiller J, Boller T, Wiemken A: Plant Journal 1998, 13:673-683. ?? Significance: Trehalose plays an important role in the desiccation
tolerance
of many organisms,
but is believed
to be
absent from plants. This paper, however, reports the cloning of a cDNA encoding one of the enzymes of trehalose biosynthesis from Arabidopsis.
Findings: Two Arabidopsis cDNAs were isolated on the basis of their ability to complement the yeast mutant tps2 which is deficient in trehalose-6-phosphate phosphatase. This enzyme is essential show
for the synthesis
significant
phosphatases
homology
of trehalose. to
other
The
plant
cDNAs
trehalose-6-phosphate
and lead to the synthesis
of trehalose
both
in
vivo and in vitro in fps2 yeast. This suggests that the trehalose biosynthetic pathway is present in Arabidopsis.
Plant-microbe
interactions
Selected by Edward Farmer University of Lausanne, Lausanne, Switzerland
Ethylene-insensitive tobacco lacks nonhost resistance against soil-borne fungi. Knoester M, van Loon LC, van den Heuvel J, Hennig J, Bol JF, Linthorst HJM: Proc Nat/ Acad Sci USA 1998, 95:i 933-l 937. ?? * Significance: This elegant paper shows the importance of ethylene perception in non-host resistance to soil-borne fungi. The authors stress that the role of ethylene perception in disease resistance depends on the pathogen (see the following alert concerning ethylene and virulent pathogens). The impaired social signalling in transgenic plants will provide the basis of many informative own right.
experiments
and
is a major
finding
in its