Tapetal-Delayed Programmed Cell Death (PCD) and Oxidative Stress-Induced Male Sterility of Aegilops uniaristata Cytoplasm in Wheat.

Zihan Liu,Xiaoyi Shi,Gan Hu,Lingli Zhang,Xiyue Song,Sha Li

doi:10.3390/ijms19061708

Abstract

Cytoplasmic male sterility (CMS) plays a crucial role in the utilization of hybrid vigor. Pollen development is often accompanied by oxidative metabolism responses and tapetal programmed cell death (PCD), and deficiency in these processes could lead to male sterility. Aegilops uniaristata cytoplasmic male sterility (Mu-CMS) wheat is a novel male-sterile line in wheat, which possess important potential in hybrid wheat breeding. However, its CMS mechanisms remain poorly understood. In our study, U87B1-706A, with the Aegilops uniaristata cytoplasm, and the maintainer line 706B were used to explore the abortive reason. Compared with 706B, histological analysis and PCD detection of the anther demonstrated that U87B1-706A appeared as delayed tapetal PCD as well as a disorganized organelle phenotype in the early uninucleate stage. Subsequently, a shrunken microspore and disordered exine structure were exhibited in the late uninucleate stage. While the activities of antioxidase increased markedly, the nonenzymatic antioxidant contents declined obviously following overacummulation of reactive oxygen species (ROS) during pollen development in U87B1-706A. Real-time quantitative PCR testified that the transcript levels of the superoxide dismutase (SOD), catalase (CAT), and ascorbate peroxidase (APX) genes, encoding pivotal antioxidant enzymes, were up-regulated in early pollen development. Therefore, we deduce excess ROS as a signal may be related to the increased expression levels of enzyme genes, thereby breaking the antioxidative system balance, resulting in delayed tapetal PCD initiation, which finally led to pollen abortion and male sterility in U87B1-706A. These results provide evidence to further explore the mechanisms of abortive pollen in CMS wheat.

Highlights

Hybrid wheat is considered as a promising approach to increase yield gains, yield stability and global productivity of wheat
Cytoplasmic male sterility (CMS) is a maternally inherited trait that results in the failure to produce functional pollen, which is widely employed for hybrid seed production to utilize heterosis in wheat [1]
We analyzed morphological and tapetal changes during different developmental stages by histological analysis and further detected the programmed cell death (PCD) though the terminal deoxynucleotidyl transferase-mediated 2 -Deoxyuridine 5 -Triphosphate nick-end labeling (TUNEL) assay and DNA laddering analysis, where we identified the period of abortion based on iodine-potassium iodide (I2-KI) staining, scanning electron microscopy (SEM) observations, and 4,6-diamidino-2-phenylindole (DAPI) staining

Summary

Introduction

Hybrid wheat is considered as a promising approach to increase yield gains, yield stability and global productivity of wheat. Cytoplasmic male sterility (CMS) is a maternally inherited trait that results in the failure to produce functional pollen, which is widely employed for hybrid seed production to utilize heterosis in wheat [1]. Tsunewaki et al [3] demonstrated that Aegilops uniaristata (Mu-type) is one of the most valuable cytoplasms for the utilization of wheat male sterility lines in 40 wheat heterogeneous lines except for Ae. kostchyi. Our previous studies have shown that the line is easier to restore, having the higher germination rate of hybrid seeds as well as powdery mildew resistance compared with other cytoplasmic male sterility lines [5,6]. The development of this line is of great value for the breeding and production of hybrid wheat, and it is an ideal material for research of cytoplasm-nuclear interaction and pollen abortion. For economically important U87B1-706A, only agronomic traits have been studied and the abortive mechanism is still not clear and has not been investigated

Methods

Results

Conclusion