15th International Conference on Arabidopsis Research - TAIR

T04-017
The Arabidopsis AtMYB60 transcription factor is
specifically expressed in guard cells and is involved
in the regulation of stomatal movements
Cominelli E(1, 1), Galbiati M(1, 1), Conti L(2, 2), Sala T(1, 1), Leonhardt N(3, 3),
Vavasseur A(3, 3), Vuylsteke M(4, 4), Dellaporta S(5, 5), Tonelli C(1, 1)
1-Dipartimento di Scienze Biomolecolari e Biotecnologie, Università degli Studi di Milano, Via
Celoria 26, 20133 Milano, Italy
2-Sainsbury Laboratory, John Innes Centre, Colney Lane, Norwich NR4 7UH, United Kingdom
3-Commissariat à l’Energie Atomique, Direction des Sciences du Vivant, Laboratoire des Echanges
Membranaires et Signalisation, F-13108 St. Paul lez Durance Cedex, France
4-Department of Plant Systems Biology, Ghent University, Technologiepark 927, B-9052 Gent,
Belgium
5-MCDB, Yale University, New Haven, CT, USA
Stomata are microscopic pores present on the epidermis of the aerial organs
of plants, playing a central role in regulating gas exchanges between plant
tissues and the atmosphere.
Land plants face the need of ensuring a sufficient uptake of CO2 for photosynthesis
and of minimizing water loss by transpiration. The regulation of
stomatal pores aperture in response to environmental stimuli including light,
humidity, CO2, and internal signals, such as the phytohormone abscissic acid
(ABA), allows the plant to cope with these conflicting needs.
An increasing number of evidences indicate a critical role for mRNA metabolism
in the control of guard cells activity and, more in general, in ABA-mediated
plant responses.
AtMYB60 gene codes for an Arabidopsis R2-R3 MYB transcription factor.
Different portions of the putative promoter of this gene were fused to reporter
genes. Expression profiles indicated that this gene is specifically expressed in
stomata guard cells.
We isolated from a collection of T-DNA mutagenized lines the atmyb60-1 null
allele. Light-induced stomatal opening was impaired in this mutant, while the
response to ABA and CO2-free air was not affected. Moreover, atmyb60-1
plants exhibited a reduction in transpirational water loss during drought. Interestingly,
the levels of the AtMYB60 transcripts were down-regulated by ABA
applications and in response to drought stress and up-regulated following
exposure to light.
Microarray analyses revealed that the transcripts of a few ABA-regulated
genes, known to be involved in the plant response to environmental stress,
were altered in the null allele.
All together our findings suggest a role for the AtMYB60 product in promoting
stomatal aperture, confirming the importance of the transcriptional control on
the mechanisms involved in regulating guard cells movements.
15 th <strong>International</strong> <strong>Conference</strong> on Arabidopsis Research 2004 · Berlin
T04-018
The impact of elevated boron on the development of
Arabidopsis thaliana
Tomas Kocabek(1), Stephen Rolfe(2), Ali Al-Zwi(2)
1-Institute of Plant Molecular Biology Academy of Sciences of the Czech Republic, Branisovska 31,
CZ-370 05 Ceské Budejovice, Czech Republic
2-University of Sheffield, Department of Animal and Plant Sciences, Sheffield, S10 2TN, United
Kingdom
Boron (B) is an essential micronutrient required for plant growth and development
but relatively little is known about the underlying processes of boron
uptake, transport, toxicity and its role at physiological concentrations within
plants. Molecular investigations of B requirement in plants could open new
possibilities for improving crops tolerant to B deficiency/toxicity stress.
The aims of this work were to: (i) characterize the response of Arabidopsis
thaliana to alterations in B supply, focusing on responses to elevated B, (ii)
examine the interactions between B response and environmental signals
(light quality and quantity), (iii) test hypotheses generated from these observations
on plants with mutations in photoreceptors and cell wall structure.
Arabidopsis seedlings were grown on 0.5x Murashige and Skoog medium
(which contains 0.1 mM B, a concentration typical of that of many soils) supplemented
with boric acid. At very high concentrations of boron (5 mM and
above) a clear toxicity effect was apparent. Seedlings were short, stunted
and pale. No toxicity effects were apparent at elevated B (1-2 mM) although
there was a clear stimulation of seedling hypocotyl elongation. This growth
stimulation was apparent in hypocotyls and petioles but not in roots, leaves
or cotyledons. Measurements of hypocotyl epidermal and cortical cell lengths
and number indicated that this growth stimulation resulted from an increase
in cell expansion rather than cell division. The stimulation of the elongation
by elevated B was proportionally more obvious with increasing irradiance.
The stimulation of hypocotyl elongation at elevated B concentrations suggests
a possible direct interaction of B with the cell wall. Thus, we have tested A.
thaliana mutants with altered cell wall compositions (mur1 ¯ mur10) (Reiter
et al., 1997). Elevated B stimulated hypocotyl elongation in mur1-4 but the
response was much reduced in mur 5-10.
The experiments were supported by the grant of Czech Science Foundation
No. 521/00/D036.
Reiter W.D., Chapple C. and Somerville C. R. (1997) Plant J. 12 : 335- 342.
T04 Interaction with the Environment 1 (Abiotic)