Comparative Cytological and Transcriptome Analysis Revealed the Normal Pollen Development Process and Up-Regulation of Fertility-Related Genes in Newly Developed Tetraploid Rice.

Jinwen Wu,Xiangdong Liu,Hang Yu,Yuanmou Chen,Hong Lin,Xiang Li,Yang Chen,Hai Zhou,Zijun Lu,Zhixiong Chen

doi:10.3390/ijms21197046

Jinwen Wu, Xiangdong Liu + Show 8 more

Open Access

https://doi.org/10.3390/ijms21197046

Copy DOI

Abstract

Autotetraploid rice is a useful germplasm for polyploid rice breeding; however, low seed setting is a major hindrance for its utilization. Here, we reported the development of a new tetraploid rice, Huoduo1 (H1), which has the characteristic of high fertility, from crossing generations of autotetraploid rice. Cytological observations displayed the high fertility of the pollen (95.62%) in H1, a lower percentage of pollen mother cell (PMC) abnormalities, and stable chromosome configurations during the pollen development process compared with its parents. Using RNA-seq analysis, we detected 440 differentially expressed genes (DEGs) in H1 compared with its parents. Of these DEGs, 193 were annotated as pollen fertility-related genes, and 129 (~66.8%) exhibited significant up-regulation in H1 compared with the parents, including three environmentally sensitive genic male sterility genes (TMS9-1, TMS5, and CSA), one meiosis gene (RAD51D), and three tapetal-related genes (MIL2, OsAP25, and OsAP37), which were validated by qRT-PCR in this study. Two genes, TMS9-1 and TMS5, were knocked out using CRISPR/Cas9 technology, and their mutants displayed low fertility and the abnormal development of pollen. Our findings provide evidence for the regulatory mechanisms of fertility in tetraploid rice and indicated that the up-regulation of pollen fertility-related genes may contribute to the high fertility in new tetraploid rice.

Highlights

Polyploidy is one of the motivations in biological evolution, and it prevalently occurs in the plant evolution process [1]
The microspores of two knock out lines degraded further after the late microspore stage and completely disappeared at the mature pollen stage, which resulted in an empty anther locule (Figure 7L–N,R,S). All of these results suggest that the lack of TMS9-1 and TMS5 caused defects in the microspores as well as abnormal pollen in H1 during pollen development
We proposed that new tetraploid rice had higher fertility and hybrid vigor, which could overcome the low fertility of autotetraploid rice [18,19]

Summary

Introduction

Polyploidy is one of the motivations in biological evolution, and it prevalently occurs in the plant evolution process [1]. 70% of plants have experienced at least one polyploidy event during their evolutionary history [2]. Several advantages, including greater variation, high biomass yield, and resistance to insect pests and diseases, are found in polyploidy species compared with their original species [3,4]. Two categories of polyploidy plants, autopolyploidy and allopolyploidy species, generally exist in nature [5]. In contrast to the higher attraction of allopolyploidy plants, little is known regarding the real appearance of autotetraploid plants in nature despite potential weaknesses, such as meiotic instability and reduced fertility. Increasing evidence indicates that the real appearance of autotetraploid plants in nature might be significantly underestimated [6]

Methods

Results

Discussion

Conclusion