Death of female flower microsporocytes progresses independently of meiosis-like process and can be accelerated by specific transcripts in Asparagus officinalis

Mayui Ide,Kiyoshi Masuda,Kaien Fujino,Daisuke Tsugama

doi:10.1038/s41598-019-39125-1

Abstract

Asparagus officinalis (garden asparagus) is a dioecious perennial crop, and the dioecy (i.e., sex) of A. officinalis can affect its productivity. In A. officinalis, flower anthers in female plants fail to accumulate callose around microsporocytes, fail to complete meiosis, and degenerate due to cell death. Although 13 genes have been implicated in the anther development of male and female flowers, it is unclear how these genes regulate the cell death in female flower anthers. The aim of this study was to narrow down factors involved in this process. TUNEL staining and Feulgen staining of female flower microsporocytes suggest that female microsporocytes enter a previously undetected meiosis-like process, and that the cell death occurs independently of this meiosis-like process, excluding the possibility that the cell death is caused by the cessation of meiosis. RNA sequencing with individual floral organs (tepals, pistils and stamens) revealed that several genes possibly regulating the cell death, such as metacaspase genes and a Bax inhibitor-1 gene, are differentially regulated between female and male flower anthers, and that genes involved in callose accumulation are up-regulated only in male flower anthers. These genes are likely involved in regulating the cell death in female flower anthers in A. officinalis.

Highlights

90% of angiosperms develop hermaphroditic flowers, which have both pistils and stamens[1]
AoMYB35 is the putative orthologue of Arabidopsis thaliana MYB35 (AtMYB35), is present only in the male genome, and is expressed in male flower stamens at a premeiotic stage[9,10]
It is unclear whether such DNA fragmentation occurs in death of cells in A. officinalis female flower anthers

Summary

Introduction

90% of angiosperms develop hermaphroditic flowers, which have both pistils and stamens[1]. The cell death in female flowers occurs first in tapetal cells, which surround microsporocytes to help their development, in microsporocytes at a stage when male flower microsporocytes would accumulate callose and complete meiosis, and in other cells[3] (see Fig. 1). Genome sequencing and RNA sequencing (RNA-Seq) have identified 13 M locus gene candidates, and two of them, SOFF (SUPPRESSOR OF FEMALE FUNCTION) and AoMYB35 (A. officinalis MYB35, known as MSE1 (MALE-SPECIFIC EXPRESSION 1) and AspTDF1 (Asparagus DEFECTIVE IN TAPETUM DEVELOPMENT AND FUNCTION 1)) are thought to be especially important[8,9,10,11,12]. Transcriptomes analyses suggest that genes involved in the cell death and the callose accumulation in anthers are differentially regulated between female and male flower anthers

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Results