ARABIDOPSIS TCH4, REGULATED BY HORMONES AND THE ENVIRONMENT, ENCODES A XYLOGLUCAN ENDOTRANSGLYCOSYLASE

Adaptation of plants to environmental conditions requires that sensing of external stimuli be linked to mechanisms of morphogenesis. The Ara bidopsis TCH (for touch) genes are rapidly upregulated in expression i n response to environmental stimuli, but a connection between this mol ecular response and developmental alterations has not been established . We identified TCH4 as a xyloglucan endotransglycosylase by sequence similarity and enzyme activity. Xyloglucan endotranslycosylases most l ikely modify cell walls, a fundamental determinant of plant form. We d etermined that TCH4 expression is regulated by auxin and brassinostero ids, by environmental stimuli, and during development, by a 1-kb regio n. Expression was restricted to expanding tissues and organs that unde rgo cell wall modification. Regulation of genes encoding cell wall-mod ifying enzymes, such as TCH4, may underlie plant morphogenetic respons es to the environment.