The Arabidopsis RING Finger E3 Ligase RHA2a Is a Novel Positive Regulator of Abscisic Acid Signaling during Seed Germination and Early Seedling Development

Qingyun Bu,Hongmei Li,Hongling Jiang,Qi Xie,Jie Zhang,Qingzhen Zhao,Xiaoyan Wu,Daowen Wang,Jiaqiang Sun,Qingzhe Zhai,Chuanyou Li

doi:10.1104/pp.109.135269

Qingyun Bu, Hongmei Li + Show 9 more

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https://doi.org/10.1104/pp.109.135269

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Journal: Plant Physiology	Publication Date: Mar 13, 2009
Citations: 161	License type: CC BY 4.0

Affiliation: State Key Laboratory of Plant Genomics

Abstract

The phytohormone abscisic acid (ABA) is well known for its regulatory roles in integrating environmental constraints with the developmental programs of plants. Here, we characterize the biological function of the Arabidopsis (Arabidopsis thaliana) RING-H2 protein RHA2a in ABA signaling. The rha2a mutant is less sensitive to ABA than the wild type during seed germination and early seedling development, whereas transgenic plants overexpressing RHA2a are hypersensitive, indicating that RHA2a positively regulates ABA-mediated control of seed germination and early seedling development. Double mutant analyses of rha2a with several known ABA-insensitive mutants suggest that the action of RHA2a in ABA signaling is independent of that of the transcription factors ABI3, ABI4, and ABI5. We provide evidence showing that RHA2a also positively regulates plant responses to salt and osmotic stresses during seed germination and early seedling development. RHA2a is a functional E3 ubiquitin ligase, and its conserved RING domain is likely important for the biological function of RHA2a in ABA signaling. Together, these results suggest that the E3 ligase RHA2a is an important regulator of ABA signaling during seed germination and early seedling development.

Highlights

The phytohormone abscisic acid (ABA) is well known for its regulatory roles in integrating environmental constraints with the developmental programs of plants
We provide evidence showing that RHA2a is a functional E3 ubiquitin ligase and that its conserved RING domain is likely important for the biological function of RHA2a in ABA signaling
When germinated on medium containing 0.5 mM ABA, the seed germination of rha2a and RHA2a-RNA interference (RNAi) 4# plants occurred earlier than in wild-type plants, whereas this concentration of ABA significantly inhibited the seed germination of 35S:RHA2a plants (Fig. 2G). These results demonstrated that, while rha2a and RHA2aRNAi 4# plants are less sensitive to ABA than wildtype plants, 35S:RHA2a plants are more sensitive to this hormone, suggesting that the RHA2a gene acts as a positive regulator of ABA signaling during seed germination

Summary

Introduction

The phytohormone abscisic acid (ABA) is well known for its regulatory roles in integrating environmental constraints with the developmental programs of plants. Initial functional evaluation has indicated that a large number of them are capable of mediating protein ubiquitination (Stone et al, 2005) Some of these RING class E3 enzymes have been implicated in specific plant signaling pathways, including ABA signaling (Callis and Vierstra, 2000; Hellmann and Estelle, 2002; Devoto et al, 2003; Moon et al, 2004; Schwechheimer and Schwager, 2004; Smalle and Vierstra, 2004; Hoecker, 2005; Huq, 2006; Dreher and Callis, 2007). SDIR1 (for SALT- AND DROUGHT-INDUCED RING FINGER1), another RING finger E3 ligase, acts upstream of ABI3 and ABI5 in ABA signaling and regulates plant responses to drought and salt stresses (Zhang et al, 2007)

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