Johnson Cameron S, Kolevski Ben, Smyth David R
School of Biological Sciences, P.O. Box 18, Clayton Campus, Monash University, Victoria 3800, Australia.
Plant Cell. 2002 Jun;14(6):1359-75. doi: 10.1105/tpc.001404.
Mutants of a new gene, TRANSPARENT TESTA GLABRA2 (TTG2), show disruptions to trichome development and to tannin and mucilage production in the seed coat. The gene was tagged by the endogenous transposon Tag1 and shown to encode a WRKY transcription factor. It is the first member of this large, plant-specific family known to control morphogenesis. The functions of all other WRKY genes revealed to date involve responses to pathogen attack, mechanical stress, and senescence. TTG2 is strongly expressed in trichomes throughout their development, in the endothelium of developing seeds (in which tannin is later generated) and subsequently in other layers of the seed coat, and in the atrichoblasts of developing roots. TTG2 acts downstream of the trichome initiation genes TTG1 and GLABROUS1, although trichome expression of TTG2 continues to occur if they are inactivated. Later, TTG2 shares functions with GLABRA2 in controlling trichome outgrowth. In the seed coat, TTG2 expression requires TTG1 function in the production of tannin. Finally, TTG2 also may be involved in specifying atrichoblasts in roots redundantly with other gene(s) but independently of TTG1 and GLABRA2.
一个新基因——透明种皮光滑2（TTG2）的突变体，表现出毛状体发育以及种皮中单宁和黏液生成的破坏。该基因被内源性转座子Tag1标记，并被证明编码一个WRKY转录因子。它是已知控制形态发生的这个庞大的植物特异性家族的首个成员。迄今为止揭示的所有其他WRKY基因的功能都涉及对病原体攻击、机械胁迫和衰老的响应。TTG2在毛状体发育的整个过程中、在发育种子的内皮层（单宁随后在其中产生）以及随后在种皮的其他层中、以及在发育根的无表皮毛细胞中强烈表达。TTG2在毛状体起始基因TTG1和无毛1的下游起作用，不过如果它们失活，TTG2在毛状体中的表达仍会继续。之后，TTG2在控制毛状体生长方面与无毛2共享功能。在种皮中，TTG2的表达在单宁生成过程中需要TTG1的功能。最后，TTG2也可能与其他基因一起在根中冗余地参与无表皮毛细胞的特化，但独立于TTG1和无毛2。
