Malcomber Simon T, Kellogg Elizabeth A
Research 223, Department of Biology, University of Missouri - St Louis, One University Boulevard, Saint Louis, MO 63121, USA.
New Phytol. 2006;170(4):885-99. doi: 10.1111/j.1469-8137.2006.01726.x.
Unisexuality has evolved repeatedly in flowering plants, but its genetic control is not understood in most cases. In maize (Zea mays), unisexual flower development is regulated by a short-chain dehydrogenase/reductase protein, TASSELSEED2 (TS2), but its role in other grass lineages is unknown. TS2 was cloned and sequenced from a broad range of grasses and compared to available sequences from other flowering plants using phylogenetic analysis and tests for selection. Gene expression was investigated using reverse transcriptase-polymerase chain reaction (RT-PCR) and in situ hybridization. TS2 orthologs appear to be restricted to monocots. The TS2 protein sequence was found to be generally under purifying selection in bisexual and unisexual lineages alike. Only one site, in unisexual herbaceous bamboos, is potentially under positive selection. TS2 was expressed broadly in all sampled tissues of unisexual and bisexual grasses, and was also expressed in rice flowers in floral organs that do not abort. TS2 may have a more general developmental role in most grasses than programmed cell death of the developing gynoecium, but has been co-opted to this role within a subset of Poaceae, probably as a result of alterations in the activity or regulation of other genes in the gynoecial pathway.
单性花在开花植物中已多次进化，但在大多数情况下其遗传控制尚不明确。在玉米（Zea mays）中，单性花发育受一种短链脱氢酶/还原酶蛋白——雄花不育2（TS2）调控，但其在其他禾本科植物谱系中的作用尚不清楚。从多种禾本科植物中克隆并测序了TS2，并通过系统发育分析和选择测试，将其与其他开花植物的现有序列进行比较。使用逆转录聚合酶链反应（RT-PCR）和原位杂交技术研究了基因表达。TS2直系同源基因似乎仅限于单子叶植物。研究发现，TS2蛋白序列在两性花和单性花谱系中通常都受到纯化选择。仅在单性草本竹类植物中的一个位点可能受到正选择。TS2在单性花和两性花禾本科植物的所有采样组织中广泛表达，在水稻花中未退化的花器官中也有表达。在大多数禾本科植物中，TS2可能在发育中具有比发育中的雌蕊程序性细胞死亡更普遍的作用，但在禾本科的一个亚组中，它可能由于雌蕊发育途径中其他基因的活性或调控发生改变而被赋予了这一作用。
