Tightly Controlled Expression of bHLH142 Is Essential for Timely Tapetal Programmed Cell Death and Pollen Development in Rice.

Swee-Suak Ko,Maurice Sun-Ben Ku,Ting-Ting Yang,Tien-Kuan Chen,Hong-Xian Hsing,Min-Jeng Li,Yi-Jyun Lin,Chung-Min Jhong

doi:10.3389/fpls.2017.01258

Abstract

Male sterility is important for hybrid seed production. Pollen development is regulated by a complex network. We previously showed that knockout of bHLH142 in rice (Oryza sativa) causes pollen sterility by interrupting tapetal programmed cell death (PCD) and bHLH142 coordinates with TDR to modulate the expression of EAT1. In this study, we demonstrated that overexpression of bHLH142 (OE142) under the control of the ubiquitin promoter also leads to male sterility in rice by triggering the premature onset of PCD. Protein of bHLH142 was found to accumulate specifically in the OE142 anthers. Overexpression of bHLH142 induced early expression of several key regulatory transcription factors in pollen development. In particular, the upregulation of EAT1 at the early stage of pollen development promoted premature PCD in the OE142 anthers, while its downregulation at the late stage impaired pollen development by suppressing genes involved in pollen wall biosynthesis, ROS scavenging and PCD. Collectively, these events led to male sterility in OE142. Analyses of related mutants further revealed the hierarchy of the pollen development regulatory gene network. Thus, the findings of this study advance our understanding of the central role played by bHLH142 in the regulatory network leading to pollen development in rice and how overexpression of its expression affects pollen development. Exploitation of this novel functionality of bHLH142 may confer a big advantage to hybrid seed production.

Highlights

Rice (Oryza sativa) is one of the most important staple crops in the world, feeding almost half of the world’s population
We demonstrated that constitutive overexpression of bHLH142 leads to male sterility in rice by triggering premature tapetal programmed cell death (PCD) via altered expression of EAT1
Overexpression of bHLH142 leads to male sterility in rice, similar to the knockout mutant reported previously (Ko et al, 2014)

Summary

Introduction

Rice (Oryza sativa) is one of the most important staple crops in the world, feeding almost half of the world’s population. Increase in rice production is urgently needed to keep pace with increasing population, especially in the face of drastic global climate change. Hybrid rice is considered the most promising strategy, and can increase rice yield by 15–20% (Khush, 2013). Many countries have successfully increased per capita rice production (Zhang, 2011). Heterosis in the F1 plants increases grain yield and produces superior phenotypes in comparison with the parents with vigor in growth, good agronomic traits and pest resistance, etc. As rice is a self-pollinated crop, adoption of a stable male sterility in the Overexpressing OsbHLH142 Causes Male Sterility female parent is critical to ensure the purity of F1 seeds. A better understanding of the mechanism underlying pollen development is important for developing new genic male sterility lines

Methods

Results

Conclusion