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, little information concerning the male sterility of CCRI9106 is known. Here, comparative transcriptome analysis of CCRI9106 (the mutant, MT) and CCRI040029 (the wild type, WT) anthers in Anyang (long-day, male sterile condition to CCRI9106) was performed to reveal the potential male sterile mechanism of CCRI9106. 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, anther RNA libraries (18 in total) of tetrad (TTP), late uninucleate (lUNP) and binucleate (BNP) stages in MT and WT were constructed 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, 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). Additionally, the ABA content of MT anthers was reduced across all stages when compared with WT anthers. At last, genes related to the formation of anther cuticle and tryphine could activated in MT under short-day condition. 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 played key regulatory roles in these processes. The conversion of fertility in different photoperiods may closely relate to the functional expression of these genes. These findings contribute to elucidate the mechanism of male sterility in upland cotton.

中文翻译：

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花药角质层和色氨酸的形成和调控缺陷导致棉花PGMS系雄性不育

雄性不育是一种简单有效的授粉控制系统，在杂交育种中得到广泛应用。据报道，在陆地棉中，CCRI9106 是一种从 CCRI040029 中分离出来的光敏遗传雄性不育 (PGMS) 突变体，它对棉花杂种优势具有很大的优势。然而，关于 CCRI9106 雄性不育的信息知之甚少。在这里，对 CCRI9106（突变体，MT）和 CCRI040029（野生型，WT）在安阳（CCRI9106 的长日雄性不育条件）的花药进行了比较转录组分析，以揭示 CCRI9106 的潜在雄性不育机制。光镜和电镜显示MT的雄性不育表型主要归因于外壁不规则、缺乏色氨酸和未成熟的花药角质层。基于 MT 花药的细胞学特征，构建了 MT 和 WT 中四分体 (TTP)、晚期单核 (lUNP) 和双核 (BNP) 阶段的花药 RNA 文库（共 18 个）用于转录组学分析，因此揭示了总共 870,4 个差异表达基因 (DEG)。通过进行基因表达模式分析和蛋白质-蛋白质相互作用（PPI）网络构建，我们发现DEGs的下调，通过脂质生物合成过程和萜类、黄酮类和类固醇等几种次生代谢物的合成途径富集，可能对MT的雄性不育表型至关重要，并导致花药角质层和色氨酸的缺陷，甚至不规则的外壁。此外，通过加权基因共表达网络分析（WGCNA）将几个脂质相关基因以及 ABA 相关基因和 MYB 转录因子鉴定为中心基因。此外，与 WT 花药相比，MT 花药的 ABA 含量在所有阶段均降低。最后，在短日照条件下，与花药角质层和色氨酸形成相关的基因可以在MT中被激活。我们提出，与花药角质层和色氨酸组装相关的基因的下调可能导致 MT 的雄性不育表型，MYB 转录因子与 ABA 在这些过程中起关键调节作用。不同光周期生育力的转换可能与这些基因的功能表达密切相关。这些发现有助于阐明陆地棉雄性不育的机制。