BHLH142 regulates various metabolic pathway-related genes to affect pollen development and anther dehiscence in rice

Rajeev Ranjan,Naveen Malik,Akhilesh K Tyagi,Reema Khurana,Saurabh Badoni,Sanjay Kapoor,Swarup K Parida

doi:10.1038/srep43397

Rajeev Ranjan, Naveen Malik + Show 5 more

Open Access

https://doi.org/10.1038/srep43397

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Abstract

Apposite development of anther and its dehiscence are important for the reproductive success of the flowering plants. Recently, bHLH142, a bHLH transcription factor encoding gene of rice has been found to show anther-specific expression and mutant analyses suggest its functions in regulating tapetum differentiation and degeneration during anther development. However, our study on protein level expression and gain-of-function phenotype revealed novel aspects of its regulation and function during anther development. Temporally dissimilar pattern of bHLH142 transcript and polypeptide accumulation suggested regulation of its expression beyond transcriptional level. Overexpression of bHLH142 in transgenic rice resulted in indehiscent anthers and aborted pollen grains. Defects in septum and stomium rupture caused anther indehiscence while pollen abortion phenotype attributed to abnormal degeneration of the tapetum. Furthermore, RNA-Seq-based transcriptome analysis of tetrad and mature pollen stage anthers of wild type and bHLH142OEplants suggested that it might regulate carbohydrate and lipid metabolism, cell wall modification, reactive oxygen species (ROS) homeostasis and cell death-related genes during rice anther development. Thus, bHLH142 is an anther-specific gene whose expression is regulated at transcriptional and post-transcriptional/translational levels. It plays a role in pollen maturation and anther dehiscence by regulating expression of various metabolic pathways-related genes.

Highlights

Ortholog, TAPETUM DEGENERATION RETARDATION (TDR) result in pollen abortion and a hypertrophic tapetum[14,15]
The transcript levels declined in the vacuolated pollen (VP) stage and were barely detectable in the mature pollen (MP) stage of anther development (Fig. 1a)
A faint band of bHLH142 protein was detected at early meiosis stage and vacuolated pollen stage but a rather strong expression was observed at tetrad and MP stage (Fig. 1b)

Summary

Introduction

Ortholog, TAPETUM DEGENERATION RETARDATION (TDR) result in pollen abortion and a hypertrophic tapetum[14,15]. TDR affects the metabolism of fatty acids and other aliphatic compounds besides regulating tapetum degeneration by directly regulating the expression of a cysteine protease gene CP114,18 Another bHLH transcription factor, ETERNAL TAPETUM1 (EAT1) has been shown to interact with TDR and regulates tapetal PCD in rice[19]. A rice MYB transcription factor encoding gene ANTHER INDEHISCENCE1 (AID1) has been shown to be involved in anther dehiscence process by regulating septum and stomium degradation[26]. Phenotypic as well as transcriptome analysis of bHLH142OE transgenic plants revealed that bHLH142 regulates anther dehiscence and tapetum degeneration process by affecting cell wall degradation and ROS signalling-related genes and it controls pollen maturation by affecting carbohydrate and lipid metabolism-related genes

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