Protein Interactomic Analysis of SAPKs and ABA-Inducible bZIPs Revealed Key Roles of SAPK10 in Rice Flowering.

Xixi Liu,Jian Zhang,Hejun Ao,Xiaohong Tong,Huimei Wang,Zhiyong Li,Yifeng Wang,Yuxuan Hou

doi:10.3390/ijms20061427

Abstract

As core components of ABA signaling pathway, SnRK2s (Sucrose nonfermenting1–Related protein Kinase 2) bind to and phosphorylate AREB/ABF (ABA responsive element binding protein/ABRE-binding factor) transcriptional factors, particularly bZIPs (basic region-leucine zipper), to participate in various biological processes, including flowering. Rice contains 10 SnRK2 members denoted as SAPK1-10 (Stress-Activated Protein Kinase) and dozens of bZIPs. However, which of the SAPKs and bZIPs pair and involve in ABA signaling remains largely unknown. In this study, we carried out a systematical protein-protein interactomic analysis of 10 SAPKs and 9 ABA-inducible bZIPs using yeast-two-hybrid technique, and identified 14 positive interactions. The reliability of Y2H work was verified by in vitro pull-down assay of the key flowering regulator bZIP77 with SAPK9 and SAPK10, respectively. Moreover, SAPK10 could phosphorylate bZIP77 in vitro. Over-expression of SAPK10 resulted in earlier flowering time, at least partially through regulating the FAC-MADS15 pathway. Conclusively, our results provided an overall view of the SAPK-bZIP interactions, and shed novel lights on the mechanisms of ABA-regulated rice flowering.

Highlights

Abscisic acid (ABA) serves as an endogenous messenger that modulates various biological processes such as seed dormancy and germination, floral transition, seedling growth, biotic and abiotic stress responses [1]
Activated SnRK2s further pass the signals to AREB/ABF TFs in the post-translational level, majorly through protein phosphorylations on their conserved motifs like RXXS/T [5], while AREB/ABF (ABRE-binding protein/ABRE-binding factor) transcription factors (TFs) activate the expression of down-stream genes to respond to the growth signals or environmental cues
Some ABA-inducible bZIPs, such as bZIP23, bZIP46 and TRAB1/bZIP66 were not included in the assay, as their protein-protein interaction relationship with all the SAPKs have been elucidated in previous studies [12,13,17]

Summary

Introduction

Abscisic acid (ABA) serves as an endogenous messenger that modulates various biological processes such as seed dormancy and germination, floral transition, seedling growth, biotic and abiotic stress responses [1]. Based on the knowledge from Arabidopsis, ABA signaling is majorly transmitted through a “PYR/PYL/RCAR-PP2C-SnRK2-AREB/ABF” cascade [2,3,4]. In this model, signals are perceived by ABA receptor complex PYR (PYrabactin Resistance 1) /PYL (PYR1-like) /RCAR (Regulatory Components of ABA Receptor)-PP2C (2C-type protein phosphatase), and transmitted to SnRK2s. Activated SnRK2s further pass the signals to AREB/ABF TFs in the post-translational level, majorly through protein phosphorylations on their conserved motifs like RXXS/T (where X stands for any amino acids, except S, T or Y) [5], while AREB/ABF (ABRE-binding protein/ABRE-binding factor) transcription factors (TFs) activate the expression of down-stream genes to respond to the growth signals or environmental cues. SnRK2-mediated phophorylation on ABI5 could delay flowering by promoting the flowering suppressor FLC (FLOWERING LOCUS) expression [11]

Methods

Results

Conclusion