Abstract
Background: Male sterility is a simple and efficient pollination control system that is widely exploited in hybrid breeding. In upland cotton, CCRI9106, a photosensitive genetic male sterile (PGMS) mutant isolated from CCRI040029, was reported of great advantages to cotton heterosis. However, the underlying molecular mechanism of CCRI9106 remains unclear.Results: In this study, light and electron microscopy revealed that the male sterility phenotype of MT was mainly attributed to irregularly exine, lacking tryphine and immature anther cuticle. Based on the cytological characteristics of MT anthers, 18 RNA libraries were constructed from the anthers of MT and WT at tetrad (TTP), late uninucleate (LUNP) and binucleate (BNP) stages of anther development for transcriptomic analysis, therefore revealing a total of 870,4 differentially expressed genes (DEGs). By performing gene expression pattern analysis and protein-protein interaction (PPI) networks construction, we found down-regulation of DEGs in cluster 2, which enriched by the lipid biosynthetic process and the synthesis pathways of several types of secondary metabolites such as terpenoids, flavonoids and steroids, may crucial to the male sterility phenotype of MT, and resulting in the defects of anther cuticle and tryphine, even the irregularly exine. Furthermore, several lipid-related genes together with ABA-related genes and MYB transcription factors were identified as hub genes via weighted gene co-expression network analysis (WGCNA), such as NPC2, LTPG, LTP1, MAKR6, Ghir_D11G032630, Ghir_A01G008890, Ghir_D01G009320, MYB3, MYB7, MYB16 and MYB48. Additionally, the ABA content of MT anthers was reduced across all stage when compared with WT anthers.Conclusions: In summary, we propose that the down-regulation of genes related to the assembly of anther cuticle and tryphine may lead to the male sterile phenotype of MT, and MYB transcription factors together with ABA play key regulatory role in these processes. These findings provide valuable information on the transcriptional level to anther and pollen development, and contribute to elucidate the mechanism of male sterility in upland cotton.