Abstract
BackgroundAegilops crassa cytoplasm is an important source for investigating cytoplasmic male sterility (CMS). Moreover, the stamens of line C303A exhibit a high degree of pistillody, turning almost white. However, the molecular mechanism that underlies pistillody in C303A remains unclear. Therefore, to obtain a better understanding of pistillody in C303A, the phenotypic and cytological features of C303A were observed to identify the key stage for the homeotic transformation of stamens into pistil-like structures. Transcriptome profiles were determined for stamens using Illumina RNA sequencing.ResultsMorphological observations of the CMS wheat line with Aegilops crassa cytoplasm C303A showed that the pistils developed normally, but the stamens were ultimately aborted and they released no pollen when mature. According to paraffin section observations, the stamens began to transform into pistils or pistil-like structures in the binucleate stage (BNS). Therefore, the stamens were collected from line C303A and its maintainer 303B in the BNS for transcriptome sequencing. In total, 20,444 wheat genes were determined as differentially expressed in C303A and 303B stamens, with 10,283 upregulated and 10,161 downregulated genes. Gene Ontology enrichment analyses showed that most of the differentially expressed genes (DEGs) were annotated with GO terms comprising metabolic process, cell, cellular process, catalytic activity, and cell part. Analysis based on the Kyoto Encyclopedia of Genes and Genomes database showed that the enriched DEGs were mainly associated with energy metabolism. We also found several essential genes that may contribute to pistillody in C303A. These findings suggest that disrupted energy metabolism and reactive oxygen metabolism induce pistillody and eventually lead to abortion in C303A.ConclusionWe determined the complex transcriptome profiles for C303A stamens and demonstrated that disrupted energy metabolism and class B MADS-box genes are related to pistillody. These findings may facilitate future studies of the mechanistic response of the wheat stamen and pollen development in CMS.
Highlights
Aegilops crassa cytoplasm is an important source for investigating cytoplasmic male sterility (CMS)
C303A is a useful material for studying pistillody in wheat, so we investigated some of the key characteristics of C303A, including its floret morphology, cytological mechanism, physiological indexes, and the molecular mechanism associated with pistillody
The results indicated that the pistillody stamens contained ovule structures, instead of pollen grains and tapetum, and the C303A stamens were unable to produce mature pollen grains that could be detected by potassium iodide staining
Summary
Aegilops crassa cytoplasm is an important source for investigating cytoplasmic male sterility (CMS). Wheat is a staple food for 35% of the world’s population [1] and the second largest staple food crop after rice, with around 220 million ha cultivated worldwide [2]. China is the largest producer and consumer of wheat throughout the world, with a cultivation area of about 24 million ha and an average yield of 4762 kg ha− 1. Increasing the wheat yield is a long-term goal of wheat breeding and the utilization of heterosis is the best method for increasing yields and satisfying global food safety requirements for crops such as maize, rape, sunflower, rice, and sorghum [4]. Male sterile plants are crucial breeding tools for harnessing hybrid vigor or heterosis in hybrid crops, and they provide valuable materials for studying stamen and pollen development as well as nuclear–cytoplasmic interactions [5]
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