Comparative transcriptome analysis and ChIP-sequencing reveals stage-specific gene expression and regulation profiles associated with pollen wall formation in Brassica rapa

Xiuping Shen,Yanhong Liu,Liai Xu,Sue Lin,Dong Zhou,Li Huang,Yuzhi Zhang,Heng Dong,Jiashu Cao

doi:10.1186/s12864-019-5637-x

Abstract

BackgroundGenic male sterility (GMS) line is an important approach to utilize heterosis in Brassica rapa, one of the most widely cultivated vegetable crops in Northeast Asia. However, the molecular genetic mechanisms of GMS remain to be largely unknown.ResultsDetailed phenotypic observation of ‘Bcajh97-01A/B’, a B. rapa genic male sterile AB line in this study revealed that the aberrant meiotic cytokinesis and premature tapetal programmed cell death occurring in the sterile line ultimately resulted in microspore degeneration and pollen wall defect. Further gene expression profile of the sterile and fertile floral buds of ‘Bcajh97-01A/B’ at five typical developmental stages during pollen development supported the result of phenotypic observation and identified stage-specific genes associated with the main events associated with pollen wall development, including tapetum development or functioning, callose metabolism, pollen exine formation and cell wall modification. Additionally, by using ChIP-sequencing, the genomic and gene-level distribution of trimethylated histone H3 lysine 4 (H3K4) and H3K27 were mapped on the fertile floral buds, and a great deal of pollen development-associated genes that were covalently modified by H3K4me3 and H3K27me3 were identified.ConclusionsOur study provids a deeper understanding into the gene expression and regulation network during pollen development and pollen wall formation in B. rapa, and enabled the identification of a set of candidate genes for further functional annotation.

Highlights

Genic male sterility (GMS) line is an important approach to utilize heterosis in Brassica rapa, one of the most widely cultivated vegetable crops in Northeast Asia
Previous cytological observation have determined that the aberrant cytokinesis at the end of meiosis caused failure of tetrads formation leading to the male sterility of the sterile line [34]
In contrast to the normally deposited callose in the cell plate of tetrads in the fertile line, the intersporal walls were absent in the tetrads of the sterile line, while, the karyokinesis was demonstrated to be normal by DAPI staining (Fig. 2)

Summary

Introduction

Genic male sterility (GMS) line is an important approach to utilize heterosis in Brassica rapa, one of the most widely cultivated vegetable crops in Northeast Asia. One of the most striking discoveries is the conversed exine regulation pathway that formed by five transcription factors, DYT1, TDF1, AMS, MYB80, and MS1 This pathway regulates tapetum development and function and thereby influences the developing microspores by controlling callose dissolution, pollen exine formation and tapetal programmed cell death [12,13,14,15,16,17]. Many other genes, such as lipid transfer protein family members and genes related to lipid and phenolic metabolism are involved in pollen exine formation [18,19,20,21,22,23,24,25,26,27,28]. The molecular mechanisms underlying pollen wall patterning remain largely elusive

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Discussion

Conclusion