Cell biology

Paper alert

ethylene inhibits the activity of the receptor related gene products and thereby derepresses ethylene responses.

stimulated

Nitric oxide functions as.a signal in plant disease resis-

exocytosis.

tance.

GTPyS

exocytosis

capacitance

concomitantly

and this effect

with an increase

could

be blocked

451

in cell

by antibodies

binding to annexin, a protein thought to play a role in control of Delledonne

M, Xia Y, Dixon RA, Lamb C: Nature 1998,

Other

signaling

or GDPOS,

metabolites

like GTP,

but

not

inhibited exocytosis.

394:585-588. 0 Significance:

A major advance

??

ease resistance Findings:

in our understanding

of dis-

is reported

NO is an impqrtant and well-characterised

signal in

animal cells. In this paper the authors show that NO also plays a key role in disease

resistance.

They show that NO levels in

plant tissud increase after challenge with Pseudomonas syringae, that the hypersensitive response in planta is inhibited by agents that block NO accumulation

and that NO induces the

expression of some but not all defence genes. The authors conclude that NO acts synergistically reactive oxygen intermediates

with and independently

in disease resistance

of

Gene regulation Selected by Bernd Weisshaar Max-Planck-lnstitut fur Ztichtungsforschung, Kcln, Germany

Two transcription factors, DREBI and DREBS, with an EREBP/APS DNA binding domain separate two cellular signal transduction pathways in drought- and low-temperature-responsive gene expression, respectively, in Arabidopsis. Liu Q, Kasuga M, Sakuma Y, Abe H, Miura S, Yamaguchi-Shinozaki K, Shinozaki K: P/ant Cell 1998, 10:1391-1406. a Significance:

signalling.

Isolation

??

dehydration-response

‘Identification and disruption of a plant shaker-like outward channel involved in K+ release into the xylem sap. Gaymard F, Pilot G, Lacombe Michaux-Ferriere

B, Bouchez

N, Thibaud

D, Bruneau

D, Boucherez

J-P, Sentenac

H:

Cell

J,

1998,

Evidence

DNA-binding

duction pathways.

Significance:

A potentially important component

in the plant

factors

acting

on

(DREs).

that two different

sequences,

detail with respect

94647-655. ??

Findings: the same recognition

of transcription

elements domain

proteins, which contain

and which

bind to identical

function in two separate

signal trans-

In addition, the factors are characterised to their transactivation

respect to effects of overexpression

potential

in transgenic

in

and with

plants.

response to drought is characterised. Findings:

The authors report the cloning and electrophysiolog-

ical characterisation (SKOR)

of an outwardly

rectifying

K+ channel

that is part of the Shaker

superfamily.

mainly in the pericycle

and parenchyma

expressed

The gene

is

cells sur-

rounding xylem vessels. This is consistent with a role for these channels

in loading

SKOR

the xylem with K+. Interestingly,

expression is downregulated be part of a mechanism

by ABA suggesting

for conserving

that this might

root K+ during periods

A novel mode of DNA recognition by a beta-sheet revealed by the solution structure of the GCC-box binding domain in complex with DNA. Allen MD, Yamasaki K, Ohme-Takagi M, Tateno M, Suzuki M: EM60 J 1998, 17:5484-5496. ?? Significance: Resolution of the 3D structure of a seemingly plant-specific DNA-binding domain. Findings: The 3-dimensional structure of the DNA-binding domain from AtERFl , an Arabidopsis thaliana protein related to ethylene-response

of drought.

determined

Defense gene induction in tobacco by nitric oxide, cyclic GMP, and cyclic ADP-ribose. Durner J, Wendehenne D, Klessig DF: Proc Nat/ Acad Sci USA 1998, 95:10328-l 0333. * Significance:

A major advance in our understanding

??

disease

resistance

Findings:

The authors report that infection of resistant but not

susceptible thase

of plant

is reported

tobacco with TMV results in an increase in NO syn-

activity.

intermediates vate defence induced

Additionally,

and

two

well-characterised

in animal NO signalling, cADPR

and cGMP,

acti-

gene expression. The authors also found that NO

defence

dependent

NO

gene

expression

and independent

NO is a signal in disease

operates

by salicylic acid

pathways. These results show that

resistance

from the

DNA-binding

domain

NMR.

was

The data are derived

in complex

with

binding-site

DNA and from aqueous solution.

Cell biology Selected by Frederic Berger Reproduction et Developpement des Plantes, Lyon, France

Relocation of a Ca*+-dependent protein kinase activity during pollen tube reorientation. Moutinho A, Trewavas AJ, Malho R: Plant Cell 1998, 10:1499-l 510. ?? Significance: This paper provides a technical advance for the localisation of protein kinase activity in viva and shows its association Findings:

signalling.

element binding proteins (EREBPs),

by multidimensional

using

with cell polar growth. The kinase activity was assayed

ratio

imaging

of

fluorescently

in pollen tubes by labelled

bisindolyl-

Ca*+, annexins, and GTP modulate exocytosis from maize root cap protoplasts. Carroll AD, Moyen C, van Kesteren P, Tooke F, Battey NH, Brownlee C: Plant Cell

growth. This localisation

1998,

tion of kinase activators and inhibitors as well as by the release

??

10:1267-i

Significance:

processes

determining

with building fuse

276. Exocytosis

is a

when

key

point

and where

in many

secretory

blocks for cell wall and plasma

with the existing

plasma

membrane.

vesicles

membrane

Here,

plant

secrete

fucose-rich

used

in patch-clamp

tance

in response

isolated

from

polysaccharides. studies to

lowing those treatments

cells

10:1427-1438. ??

signal

whole-cell metabolites.

with tip

by the external applica-

of high kinase activity fol-

resulted in growth reorientation.

Localized upregulation of a new expansin gene predids the site of leaf formation in the tomato meristem. Reinhardt D, Wittwer F, Mandel T, Kuhlemeier C: P/ant Cell 1998,

were

root

was modified

of caged Ca*+. The new localisation

cap

maize

kinase C. A higher kinase

activity at the tip of the pollen tube was correlated

These protoplasts

monitoring

various

an inhibitor of protein

will

a detailed

analysis of signals mediating exocytosis in maize root cap cells has been performed. Findings: Protoplasts

maleimide,

capaciCa*+

* Significance:

Together with an older study by the same group

(Fleming et a/. 1997, Science

276:1415-1418)

this work con-

tributes to outline the roles of cell growth during development.

452

Paper alert

Findings: Whereas expressed

most

expansins

(cell wall

proteins)

are

in expanding tissues, the expression of the expansin

LeExp18

is confined

meristem

LeExp78

expression

to meristematic

mordium

initiation

before

tissues.

is elevated

visible

histological

before mitotic activity can be detected.

In the shoot

at the site of prichanges

and

Since external applica-

P, Tooke F, Battey NH, Brownlee C: Plant Cell 10:1267-l 276. ?? Significance: Direct evidence is provided for a role for annexKerteren 1998,

ins in plant exocytotic regulation. Findings:

In situ hybridisation

shows

that the expression

tion of expansins can cause primordium induction, it is possible

tains hypersecretory

to speculate

these cells allows to monitor variations of the membrane

a crucial role of cell expansion in the organisation

of the shoot apical meristem.

of

annexins in maize roots is localised in the root cap which con-

itance

which

capacitance

cells. Patch-clamping

is proportional corresponds

of protoplasts

to cell surface.

from

capac-

An increase

in

to a net increase in exocytotic activi-

Identification and disruption of a plant shaker-like outward channel involved in K+ release into the xylem sap. Gaymard F, Pilot G, Lacombe B, Bouchez D, Bruneau D, Boucherez J, Michaux-Ferriere N, Thibaud J-B, Sentenac H: Cell 1998, 94647-655. ?? * Significance: The molecular and functional characterisation

ty. Both Cap+ and annexins applied internally appear to regulate

of the K+ channel SKOR

Vernhettes

leads to the identification

of its role in

synergetically

the intensity of exocytosis.

plasma membrane-bound putative endo-1,4-BD-glucanase is required for normal wall assembly and cell elongation in Arabidopsis. Nicol F, His I, Jauneau A,

A

S,

Canut

H,

Hofte

H:

EMBO

J

1998,

K+ release in the xylem sap, a process essential for plant life.

19:5563-5576.

Findings:

Significance: The isolation of an endoglucanase using a TDNA tagged mutant sheds light on the role of this class of enzymes in cell elongation. Findings: The mutant korrigan is characterised by an alteration

was

identified

by its homology

to other

known plant shaker-like

SKOR

channels.

Electrophysiological

charac-

terisation of the channel expressed outward release.

rectifying

properties

In Arabidopsis

cycle and in parenchyma Mutants for SKOR are characterised

in Xenopus

compatible’with

roots SKOR

oocytes

is expressed

cells surrounding

in the peri-

the xylem vessels.

isolated using a reverse genetics by a decrease

shows

a role in K+

approach

in K+ content in the sap.

??

of cell elongation The mutation served

in dicots

membrane

in all cell types excluding

affects

the function

and monocots.

and

maize

protoplasts.

root

cap

GTP

modulate Carroll

exocytosis AD,

Moyen

from C,

van

cells. con-

This enzyme

in an integral

protein and is probably involved in the assembly

the cellulose-hemicellulose

Ca2+, annexins,

tip-growing

of an endoglucanase

network. KOR mRNA

ed at the onset of hypocotyl growth and down-regulated dwarf mutant det2 deficient in brassinosteroids.

of

is up-regulatin the