Impact of Autophagy on Gene Expression and Tapetal Programmed Cell Death During Pollen Development in Rice.

Shigeru Hanamata,Jumpei Sawada,Seisuke Kimura,Ken–Ichi Nonomura,Kazuyuki Kuchitsu,Kazunori Ogawa,Togo Fukunaga,Seijiro Ono,Takamitsu Kurusu

doi:10.3389/fpls.2020.00172

Abstract

Autophagy has recently been shown to be required for tapetal programmed cell death (PCD) and pollen maturation in rice. A transcriptional regulatory network is also known to play a key role in the progression of tapetal PCD. However, the relationship between the gene regulatory network and autophagy in rice anther development is mostly unknown. Here, we comprehensively analyzed the effect of autophagy disruption on gene expression profile during the tapetal PCD in rice anther development using high-throughput RNA sequencing. Expression of thousands of genes, including specific transcription factors and several proteases required for tapetal degradation, fluctuated synchronously at specific stages during tapetal PCD progression in the wild-type anthers, while this fluctuation showed significant delay in the autophagy-deficient mutant Osatg7-1. Moreover, gene ontology enrichment analysis in combination with self-organizing map clustering as well as pathway analysis revealed that the expression patterns of a variety of organelle-related genes as well as genes involved in carbohydrate/lipid metabolism were affected in the Osatg7-1 mutant during pollen maturation. These results suggest that autophagy is required for proper regulation of gene expression and quality control of organelles and timely progression of tapetal PCD during rice pollen development.

Highlights

Reproductive development, both in animals and plants, requires drastic metabolic changes for nutrient supply to gametes
The tapetum acts as a nutritional source for the developing microspores by undergoing degeneration triggered by programmed cell death (PCD) from stage 7 (ST7) to ST11 (Ariizumi and Toriyama, 2011; Zhang and Yang, 2014)
Transmission electron microscopy (TEM) analysis has shown that the morphology of tapetum at ST8–9 is normal, but the tapetal collapse is significantly delayed and intracellular structures including mitochondria and plastids remained at mature pollen stage in the autophagy-deficient mutant Osatg7-1 (Hanamata et al, 2014; Kurusu et al, 2014), suggesting that autophagy contributes to tapetal degradation and PCD in rice

Summary

INTRODUCTION

Reproductive development, both in animals and plants, requires drastic metabolic changes for nutrient supply to gametes. Transcriptomics and metabolomics in autophagy-deficient mutants of Arabidopsis (atatg5-1) and maize (Zmatg12) suggest the importance of autophagy in cell homeostasis and stress responses These multi-omics provides comprehensive data sets for the identification of proteins, protein complexes, organelles and processes directly or indirectly under autophagic control. Transmission electron microscopy (TEM) analysis has shown that the morphology of tapetum at ST8–9 is normal, but the tapetal collapse is significantly delayed and intracellular structures including mitochondria and plastids remained at mature pollen stage in the autophagy-deficient mutant Osatg (Hanamata et al, 2014; Kurusu et al, 2014), suggesting that autophagy contributes to tapetal degradation and PCD in rice. Role of autophagy in the synchronized progression of tapetal PCD, metabolisms of carbohydrates and lipids and the quality control of organelles during rice anther/ pollen development are discussed

MATERIALS AND METHODS

1.1–1.2 Transparent

RESULTS AND DISCUSSION