Characterization of germline development and identification of genes associated with germline specification in pineapple

Lihua Zhao,Xingyue Jin,Adrien Sicard,Liping Liu,Xianying Dou,Yuan Qin,Xiaomei Wang,Lulu Wang,Heming Zhao,Zhimin Hou,Hanyang Cai,Yanhui Liu,Mohammad Aslam,Yi Li

doi:10.1038/s41438-021-00669-x

Abstract

Understanding germline specification in plants could be advantageous for agricultural applications. In recent decades, substantial efforts have been made to understand germline specification in several plant species, including Arabidopsis, rice, and maize. However, our knowledge of germline specification in many agronomically important plant species remains obscure. Here, we characterized the female germline specification and subsequent female gametophyte development in pineapple using callose staining, cytological, and whole-mount immunolocalization analyses. We also determined the male germline specification and gametophyte developmental timeline and observed male meiotic behavior using chromosome spreading assays. Furthermore, we identified 229 genes that are preferentially expressed at the megaspore mother cell (MMC) stage during ovule development and 478 genes that are preferentially expressed at the pollen mother cell (PMC) stage of anther development using comparative transcriptomic analysis. The biological functions, associated regulatory pathways and expression patterns of these genes were also analyzed. Our study provides a convenient cytological reference for exploring pineapple germline development and a molecular basis for the future functional analysis of germline specification in related plant species.

Highlights

In sexually reproducing organisms, the establishment of the germline initiates the transition toward the haploid phase of the life cycle and leads to the production of gametes
We recently showed that the spatial restriction of the biogenesis and mobility of a TAS3-derived trans-acting small interfering RNA targeting AUXIN RESPONSE FACTORs (ARF), tasiR-ARF, restricted megaspore mother cell (MMC) differentiation to a single cell[13,14]
Within the AGNZZ/SPL gene regulatory network (GRN), we found that AcAG, AcWUS, AcPIN1 and AcWIH2 were highly expressed in MMC-stage ovules and pollen mother cell (PMC)-stage anthers

Summary

Introduction

The establishment of the germline initiates the transition toward the haploid phase of the life cycle and leads to the production of gametes. The MADS-box homeotic gene AGAMOUS (AG) initiates germline specification by activating the SPOROCYTELESS/NOZZLE (SPL/NZZ) transcription factor in the ovule and anther primordia[5]. SPL/NZZ, in turn, activates the homeotic gene WUSCHEL (WUS), which regulates ovule patterning and initiates MMC formation[6]. The expression of WUS and SPL/NZZ is promoted by the receptors of the plant hormone cytokinin receptors ARABIDOPSIS HISTIDINE KINASE4/CYTOKININ RESPONSE1 (AHK4/CRE1), AHK2 and AHK3. SPL/NZZ activates the expression of the auxin transporter gene PINFORMED1 (PIN1), establishing a specific phytohormone gradient required for germline initiation[8,9]

Methods

Results

Conclusion