The Major Factors Causing the Microspore Abortion of Genic Male Sterile Mutant NWMS1 in Wheat (Triticum aestivum L.)

Abstract

Male sterility is a valuable trait for genetic research and production application of wheat (Triticum aestivum L.). NWMS1, a novel typical genic male sterility mutant, was obtained from Shengnong 1, mutagenized with ethyl methane sulfonate (EMS). Microstructure and ultrastructure observations of the anthers and microspores indicated that the pollen abortion of NWMS1 started at the early uninucleate microspore stage. Pollen grain collapse, plasmolysis, and absent starch grains were the three typical characteristics of the abnormal microspores. The anther transcriptomes of NWMS1 and its wild type Shengnong 1 were compared at the early anther development stage, pollen mother cell meiotic stage, and binucleate microspore stage. Several biological pathways clearly involved in abnormal anther development were identified, including protein processing in endoplasmic reticulum, starch and sucrose metabolism, lipid metabolism, and plant hormone signal transduction. There were 20 key genes involved in the abnormal anther development, screened out by weighted gene co-expression network analysis (WGCNA), including SKP1B, BIP5, KCS11, ADH3, BGLU6, and TIFY10B. The results indicated that the defect in starch and sucrose metabolism was the most important factor causing male sterility in NWMS1. Based on the experimental data, a primary molecular regulation model of abnormal anther and pollen developments in mutant NWMS1 was established. These results laid a solid foundation for further research on the molecular mechanism of wheat male sterility.which is one of the key ways to improve wheat yield [6]. Male sterility permits the production of hybrids on a commercial scale, relying on heterosis in crops, and can greatly increase selection efficiency of the yield [7]. In-depth understanding of the molecular mechanism of male sterility can help us to use it more effectively.Plant male sterility was first reported in the 18th century [8]. A large number of plant male sterility mutants have been reported over the past few decades. Male sterility includes cytoplasmic male sterility (CMS) controlled by mitochondrial genes coupled with nuclear genes, and genic male sterility (GMS) controlled by nuclear genes alone [9][10][11]. The pistils of the cytoplasmic male sterile lines and genic male sterile lines are normal, but their stamens are abnormal and cannot pollinate normally, which is due to stamen degeneration, pollen abortion, or functional sterility. GMS occurs in 216 species and 17 species crosses, while CMS occurs in more than 150 species and 271 species crosses [11][12][13]. Plant male sterility lines have been widely studied and applied successfully in many crops, such as maize (Zea mays), rice (Oryza sativa), soybean (Glycine max), and barley (Hordeum vulgare). Several wheat CMS lines have been studied and applied in production; however, commercial application is limited [14][15][16]. Possible applications of GMS in plant breeding have been reviewed and discussed for at least 30 years [17]. Up to now, only five GMS genes have been...

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