Plant Cell Hybrigenics
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First published online August 7, 2009; 10.1105/tpc.109.067702

The Plant Cell 21:2253-2268 (2009)
© 2009 American Society of Plant Biologists

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Abscisic Acid Represses Growth of the Arabidopsis Embryonic Axis after Germination by Enhancing Auxin Signaling[W]

Christophe Belina, Christian Megiesa, Eva Hauserováb,c and Luis Lopez-Molinaa,1

a Département de Biologie Végétale, Université de Genève, 1211 Genève 4, Switzerland
b Laboratory of Growth Regulators, Faculty of Science, Palacky University, CZ-78371 Olomouc, Czech Republic
c Swedish University of Agricultural Science, Umea Plant Science Center, Department of Forest Genetics and Plant Physiology, Umea 901 83, Sweden

1 Address correspondence to luis.lopezmolina{at}unige.ch.

Under unfavorable environmental conditions, the stress phytohormone ABA inhibits the developmental transition from an embryo in a dry seed into a young seedling. We developed a genetic screen to isolate Arabidopsis thaliana mutants whose early seedling development is resistant to ABA. Here, we report the identification of a recessive mutation in AUXIN RESISTANT1 (AUX1), encoding a cellular auxin influx carrier. Although auxin is a major morphogenesis hormone in plants, little is known about ABA–auxin interactions during early seedling growth. We show that aux1 and pin2 mutants are insensitive to ABA-dependent repression of embryonic axis (hypocotyl and radicle) elongation. Genetic and physiological experiments show that this involves auxin transport to the embryonic axis elongation zone, where ABA enhances the activity of an auxin-responsive promoter. We propose that ABA represses embryonic axis elongation by potentiating auxin signaling in its elongation zone. This involves repression of the AUXIN INDUCIBLE (Aux/IAA) gene AXR2/IAA7, encoding a key component of ABA- and auxin-dependent responses during postgerminative growth.






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