OsMADS23 phosphorylated by SAPK9 confers drought and salt tolerance by regulating ABA biosynthesis in rice.

Xingxing Li,Zizhao Xie,Junli Huang,Gregory P. Copenhaver,Rongfeng Zeng,Bo Yu,Qian Min,Qi Wu

doi:10.1371/journal.pgen.1009699

Abstract

Some of MADS-box transcription factors (TFs) have been shown to play essential roles in the adaptation of plant to abiotic stress. Still, the mechanisms that MADS-box proteins regulate plant stress response are not fully understood. Here, a stress-responsive MADS-box TF OsMADS23 from rice conferring the osmotic stress tolerance in plants is reported. Overexpression of OsMADS23 remarkably enhanced, but knockout of the gene greatly reduced the drought and salt tolerance in rice plants. Further, OsMADS23 was shown to promote the biosynthesis of endogenous ABA and proline by activating the transcription of target genes OsNCED2, OsNCED3, OsNCED4 and OsP5CR that are key components for ABA and proline biosynthesis, respectively. Then, the convincing evidence showed that the OsNCED2-knockout mutants had lower ABA levels and exhibited higher sensitivity to drought and oxidative stress than wild type, which is similar to osmads23 mutant. Interestingly, the SnRK2-type protein kinase SAPK9 was found to physically interact with and phosphorylate OsMADS23, and thus increase its stability and transcriptional activity. Furthermore, the activation of OsMADS23 by SAPK9-mediated phosphorylation is dependent on ABA in plants. Collectively, these findings establish a mechanism that OsMADS23 functions as a positive regulator in response to osmotic stress by regulating ABA biosynthesis, and provide a new strategy for improving drought and salt tolerance in rice.

Highlights

Plants are often exposed to various environmental stresses, and drought and high salinity are major stress factors that impair plant growth and productivity of crops [1]
Two T-DNA insertion mutant alleles of OsMADS23, M1 and M2, were obtained, and they have different DNA insertion sites in the third intron of OsMADS23 (S1A Fig). We found that both M1 (-/-) and M2 (+/-) showed reduced growth indicated by plant height, compared to their corresponding wild type Zhonghua 11 (Z11) (Figs 1A–1G and S1B–S1D)
To test whether OsMADS23 regulates the expression of abscisic acid (ABA) or proline synthetic genes in vivo, we performed ChIP-qPCR and transient transactivation assays, and the results showed that OsMADS23 could directly activate the transcription of OsNCED3, OsNCED4 and OsP5CR, respectively, by recognizing the CArG-box motifs in their promoter regions (Fig 7)

Summary

Introduction

Plants are often exposed to various environmental stresses, and drought and high salinity are major stress factors that impair plant growth and productivity of crops [1]. SAPK9 is shown to activate OsbZIP46 by phosphorylation under ABA or drought stress treatment in rice [15,16]. It is demonstrated SAPK10 phosphorylates TRAB1 and OsbZIP77 in vitro [14,17]. SAPK2 is found to be able to activate OsbZIP23 and OsbZIP46 by phosphorylation and promote the transcription of a large number of genes with functions in stress responses [15,16,18], which further expands our understanding on the functions of SAPKs in ABA signaling

Methods

Results

Discussion

Conclusion