MIR156-Targeted SPL9 Is Phosphorylated by SnRK2s and Interacts With ABI5 to Enhance ABA Responses in Arabidopsis.

Huixue Dong,Yingfang Zhu,Ruizhen Yang,Suli Yan,Yunwei Zhang,Yexing Jing,Jiaqiang Sun,Yun Zhou

doi:10.3389/fpls.2021.708573

Abstract

The miR156-targeted SQUAMOSA PROMOTER BINDING PROTEIN-LIKE (SPL) transcription factors play key roles in regulating plant development, but little is known about their function in abscisic acid (ABA) signaling. Here, we report that the miR156-targeted SPLs enhance ABA responses and contribute to the inhibition of pre-harvest sprouting. We find that SPL9 directly activates the expression of ABA responsive genes through binding to their promoters. SPL9 was further shown to physically interact with ABSCISIC ACID INSENSITIVE 5 (ABI5), a master transcription factor in ABA signaling, thus promoting its association with the promoters of ABA responsive genes. Furthermore, we reveal that the protein kinases SnRK2s interact with and phosphorylate SPL9, which is essential for its role in the activation of ABA responses. Together, our results disclose a SnRK2s-SPLs-ABI5 regulatory module in ABA signaling in Arabidopsis.

Highlights

The stress-related phytohormone abscisic acid (ABA) inhibits seed germination and seedling growth to adapt various environmental challenges (Cutler et al, 2010; Weiner et al, 2010)
The GFP-rSPL9 line is identical to a gainof-function mutant of SPL9 gene, in which a miR156-resistant version of SPL9 is expressed from its native promoter (Wang et al, 2009), and the MIM156 line has elevated expression of SPL9 and other SQUAMOSA PROMOTER BINDING PROTEIN-LIKE (SPL) (Wang et al, 2009)
The miR156-regulated SPL9 appears to play a positive role in regulating ABA responses

Summary

Introduction

The stress-related phytohormone abscisic acid (ABA) inhibits seed germination and seedling growth to adapt various environmental challenges (Cutler et al, 2010; Weiner et al, 2010). Several SNF1 (sucrose non-fermenting 1)-related kinase 2s (SnRK2s), including SnRK2.2, SnRK2.3, and SnRK2.6 ( known as Open Stomata 1, OST1), were identified as stress- or ABA-activated protein kinases and function redundantly in ABA-mediated regulation of seed germination, seedling growth, drought stress and stomatal closure (Mustilli et al, 2002; Fujii et al, 2007; Nakashima et al, 2009; Ding et al, 2015; Huang et al, 2018)

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Conclusion