Transcript Profiling Analysis and ncRNAs' Identification of Male-Sterile Systems of Brassica campestris Reveal New Insights Into the Mechanism Underlying Anther and Pollen Development.

Dong Zhou,Xinpeng Xiong,Jiashu Cao,Dandan Liu,Tao Lyu,Li Huang,Sue Lin,Jingwen Chen,Caizhi Chen,Zongmin Jin

doi:10.3389/fpls.2022.806865

Abstract

Male-sterile mutants are useful materials to study the anther and pollen development. Here, whole transcriptome sequencing was performed for inflorescences in three sterile lines of Chinese cabbage (Brassica campestris L. ssp. chinensis Makino, syn. B. rapa ssp. chinensis), the genic male-sterile line (A line), the Polima cytoplasmic male-sterile (CMS) line (P line), and the Ogura CMS line (O line) along with their maintainer line (B line). In total, 7,136 differentially expressed genes (DEGs), 361 differentially expressed long non-coding RNAs (lncRNAs) (DELs), 56 differentially expressed microRNAs (miRNAs) (DEMs) were selected out. Specific regulatory networks related to anther cell differentiation, meiosis cytokinesis, pollen wall formation, and tapetum development were constructed based on the abortion characteristics of male-sterile lines. Candidate genes and lncRNAs related to cell differentiation were identified in sporocyteless P line, sixteen of which were common to the DEGs in Arabidopsis spl/nzz mutant. Genes and lncRNAs concerning cell plate formation were selected in A line that is defected in meiosis cytokinesis. Also, the orthologs of pollen wall formation and tapetum development genes in Arabidopsis showed distinct expression patterns in the three different sterile lines. Among 361 DELs, 35 were predicted to interact with miRNAs, including 28 targets, 47 endogenous target mimics, and five precursors for miRNAs. Two lncRNAs were further proved to be functional precursors for bra-miR156 and bra-miR5718, respectively. Overexpression of bra-miR5718HG in B. campestris slowed down the growth of pollen tubes, caused shorter pollen tubes, and ultimately affected the seed set. Our study provides new insights into molecular regulation especially the ncRNA interaction during pollen development in Brassica crops.

Highlights

Anther development starts from an archesporial cell that produces sporogenous cells that further differentiate into the endothecium, middle layer, tapetum, and pollen mother cells (PMCs) (Murmu et al, 2010)
As the general morphology of inflorescences and flowers of the three sterile lines did not differ from those of the common fertile maintainer line except for the anthers, inflorescences without opened flowers of A line, P line, Ogura CMS line (O line), and B line were taken for transcriptome sequencing to analyze the transcriptome during pollen and anther development (Figure 1A)
No line-specific differentially expressed miRNAs (DEMs) were found in the A line, 20 DEMs were expressed in the P line, and only six DEMs were expressed in the O line

Summary

Introduction

Anther development starts from an archesporial cell that produces sporogenous cells that further differentiate into the endothecium, middle layer, tapetum, and pollen mother cells (PMCs) (Murmu et al, 2010). Pollen development can be divided into two major phases: the developmental phase and the functional phase (Hafidh and Honys, 2021). The developmental stage of pollen is initiated by the meiosis of diploid PMCs. Tetrads formed by four haploid microspores are generated after simultaneoustype cytokinesis in dicotyledon, which means cell plates form between four haploid nuclei simultaneously (De Storme and Geelen, 2013). AtNACK2, MAPKK6, and MAPK4 function in male-specific meiotic cytokinesis while no evidence showed that ANP1 and ANP3 work in male meiosis as yet (Yang et al, 2003; Zeng et al, 2011). In contrast to mitotic cytokinesis, little is known about the regulatory network underlying plant male meiotic cytokinesis

Methods

Results

Conclusion