Gene-Specific Changes in α-Tubulin Transcript Accumulation in Developing Cotton Fibers

The fibers of cotton (Gossypium hirsutum) are single-cell trichomes that undergo rapid and synchronous elongation. Cortical microtubules provide spatial information necessary for the alignment of cellulose microfibrils that confine and regulate cell elongation. We used gene-specific probes to investigate α-tubulin transcript levels in elongating cotton fibers. Two discrete patterns of transcript accumulation were observed. Whereas transcripts of α-tubulin genes GhTua2/3 and GhTua4 increased in abundance from 10 to 20 d post anthesis (DPA), GhTua1 and GhTua5 transcripts were abundant only through to 14 DPA, and dropped significantly at 16 DPA with the onset of secondary wall synthesis. This is the first report, to our knowledge, of gene-specific changes in tubulin transcript levels during the development of a terminally differentiated plant cell. The decrease in abundance of GhTua1 and GhTua5 transcripts was correlated with pronounced changes in cell wall structure, suggesting that α-tubulin isoforms may be functionally distinct in elongating fiber cells. Although total α-tubulin transcript levels were much higher in fiber than several other tissues, including the hypocotyl and pollen, none of the α-tubulins was specific to fiber cells.

陆地棉（Gossypium hirsutum）的棉纤维为单细胞毛状体，其伸长过程兼具快速性与同步性。皮层微管可为约束并调控细胞伸长的纤维素微纤丝的排列提供必要的空间定位信息。本研究采用基因特异性探针，对正在伸长的棉纤维中的α-微管蛋白（α-tubulin）转录本水平进行了检测分析。研究观察到两类截然不同的转录本积累模式：α-微管蛋白基因GhTua2/3与GhTua4的转录本丰度在开花后10天至20天（DPA）间持续上升；而GhTua1与GhTua5的转录本仅在开花后14天内维持较高丰度，在次生壁合成起始的开花后16天时其丰度显著下降。据我们所知，本研究首次报道了终末分化植物细胞发育过程中，微管蛋白转录本水平出现的基因特异性变化。GhTua1与GhTua5转录本的丰度下降与细胞壁结构的显著变化呈相关性，这表明不同的α-微管蛋白同工型在伸长的纤维细胞中可能存在功能分化。尽管棉纤维中的总α-微管蛋白转录本水平远高于下胚轴、花粉等其他多种组织，但并未有任何一种α-微管蛋白仅在棉纤维细胞中特异性表达。