Liu Xi-Qiong, Liu Zhi-Quan, Yu Cheng-Yu, Dong Jun-Gang, Hu Sheng-Wu, Xu Ai-Xia
Department of Plant Science and Technology, College of Agronomy, Northwest A&F UniversityYangling, China.
Front Plant Sci. 2017 Jul 20;8:1268. doi: 10.3389/fpls.2017.01268. eCollection 2017.
The thermo-sensitive genic male sterility (TGMS) line SP2S is a spontaneous rapeseed mutation with several traits that are favorable for the production of two-line hybrids. To uncover the key cellular events and genetic regulation associated with TGMS expression, a combined study using cytological observation, transcriptome profiling, and gene expression analysis was conducted for SP2S and its near-isogenic line SP2F grown under warm conditions. Asynchronous microsporocyte meiosis and abnormal tapetal plastids and elaioplasts were demonstrated in the anther of SP2S. The tetrad microspore did not undergo mitosis before the cytoplasm degenerated. Delayed degradation of the tetrad wall, which led to tetrad microspore aggregation, resulted in postponement of sexine (outer layer of pollen exine) formation and sexine fusion in the tetrad. The nexine (foot layer of exine) was also absent. The delay of tetrad wall degradation and abnormality of the exine structure suggested that the defective tapetum lost important functions. Based on transcriptomic comparisons between young flower buds of SP2S and SP2F plants, a total of 465 differentially expressed transcripts (DETs) were identified, including 303 up-regulated DETs and 162 down-regulated DETs in SP2S. Several genes encoding small RNA degrading nuclease 2, small RNA 2'-O-methyltransferase, thioredoxin reductase 2, regulatory subunit A alpha isoform of serine/threonine-protein phosphatase 2A, glycine rich protein 1A, transcription factor bHLH25, leucine-rich repeat receptor kinase At3g14840 like, and fasciclin-like arabinogalactan proteins FLA19 and FLA20 were greatly depressed in SP2S. Interestingly, a gene encoding the Arabidopsis MS5 homologous protein, which is necessary for microsporocyte meiosis, was down-regulated in SP2S. Other genes that were up-regulated in SP2S encoded glucanase A6, ethylene-responsive transcription factor 1A-like, pollen-specific SF3, stress-associated endoplasmic reticulum protein 2, WRKY transcription factors and pentatricopeptide repeat (PPR) protein At1g07590. The tapetum-development-related genes, including , and , were slightly up-regulated in 3-mm-long flower buds or their anthers, and their downstream genes, and , which affect callose dissolution and exine formation, were greatly up-regulated in SP2S. This aberrant genetic regulation corresponded well with the cytological abnormalities. The results suggested that expression of TGMS associates with complex transcriptional regulation.
温敏雄性不育系（TGMS）SP2S是油菜的一个自发突变体，具有多个有利于两系杂交种生产的性状。为了揭示与TGMS表达相关的关键细胞事件和遗传调控，对在温暖条件下生长的SP2S及其近等基因系SP2F进行了细胞学观察、转录组分析和基因表达分析的联合研究。在SP2S的花药中发现了不同步的小孢子母细胞减数分裂以及异常的绒毡层质体和造油体。四分体小孢子在细胞质退化之前没有进行有丝分裂。四分体壁延迟降解导致四分体小孢子聚集，从而导致花粉外壁外层（外壁）形成和四分体中外壁融合延迟。内壁（外壁基足层）也不存在。四分体壁降解延迟和外壁结构异常表明有缺陷的绒毡层失去了重要功能。基于SP2S和SP2F植株幼嫩花芽的转录组比较，共鉴定出465个差异表达转录本（DETs），其中SP2S中有303个上调的DETs和162个下调的DETs。几个编码小RNA降解核酸酶2、小RNA 2'-O-甲基转移酶、硫氧还蛋白还原酶2、丝氨酸/苏氨酸蛋白磷酸酶2A调节亚基Aα异构体、富含甘氨酸蛋白1A、转录因子bHLH25、富含亮氨酸重复受体激酶At3g14840类似物以及类成束蛋白阿拉伯半乳聚糖蛋白FLA19和FLA20的基因在SP2S中被大幅下调。有趣的是，一个编码拟南芥MS5同源蛋白（小孢子母细胞减数分裂所必需）的基因在SP2S中被下调。在SP2S中上调的其他基因编码葡聚糖酶A6、乙烯响应转录因子1A类似物、花粉特异性SF3、应激相关内质网蛋白2、WRKY转录因子和五肽重复（PPR）蛋白At1g07590。与绒毡层发育相关的基因，包括 和 ，在3毫米长的花芽或其花药中略有上调，而它们影响胼胝质溶解和外壁形成的下游基因 和 在SP2S中大幅上调。这种异常的遗传调控与细胞学异常非常吻合。结果表明TGMS的表达与复杂的转录调控有关。
