Abstract
Auxin regulates a plethora of events during plant growth and development, acting in concert with other phytohormones. YUCCA genes encode flavin monooxygenases that function in tryptophan-dependent auxin biosynthesis. To understand the contribution of the YUCCA4 (YUC4) gene on auxin homeostasis, plant growth and interaction with abscisic acid (ABA) signaling, 35S::YUC4 seedlings were generated, which showed elongated hypocotyls with hyponastic leaves and changes in root system architecture that correlate with enhanced auxin responsive gene expression. Differential expression of PIN1, 2, 3 and 7 auxin transporters was detected in roots of YUC4 overexpressing seedlings compared to the wild-type: PIN1 was down-regulated whereas PIN2, PIN3 and PIN7 were up-regulated. Noteworthy, 35S::YUC4 lines showed enhanced sensitivity to ABA on seed germination and post-embryonic root growth, involving ABI4 transcription factor. The auxin reporter genes DR5::GUS, DR5::GFP and BA3::GUS further revealed that abscisic acid impairs auxin responses in 35S::YUC4 seedlings. Our results indicate that YUC4 overexpression influences several aspects of auxin homeostasis and reveal the critical roles of ABI4 during auxin-ABA interaction in germination and primary root growth.
Highlights
IntroductionThe phytohormone auxin (indole-3-acetic acid, IAA) plays a role in many aspects of plant growth and development, including cell division, growth and differentiation
The phytohormone auxin plays a role in many aspects of plant growth and development, including cell division, growth and differentiation
35S::YUC4 Arabidopsis plants show phenotypes related to auxin overproduction
Summary
The phytohormone auxin (indole-3-acetic acid, IAA) plays a role in many aspects of plant growth and development, including cell division, growth and differentiation. It mediates adaptation to biotic and abiotic stress (Ghanashyam and Jain, 2009; Rahman, 2013). These functions require coordinated IAA biosynthesis, degradation, conjugation, transport and signaling for which specific genes and proteins have been identified in Arabidopsis and crops. Enzymes of the YUCCA family of flavin-containing mono-oxygenases (FMOs) catalyze the conversion of indole-pyruvic acid (IPA) into IAA. This two-step auxin biosynthesis pathway is highly conserved throughout the plant kingdom and is essential for almost all of the major
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