Abstract
ZIM is a putative transcription factor in Arabidopsis with zinc-finger and CCT motifs. ZIM mRNA was detected from the vegetative phase and was more abundant in apices than leaves. To elucidate ZIM function, ZIM-overexpressing transgenic plants (ZIM-ox) were generated. In ZIM-ox, hypocotyls and petioles were elongated due to increased cell elongation. Competence in cell elongation was not affected, since ZIM-ox hypocotyls were as long as wild-type in the dark. The hypocotyl elongation phenotype was also observed in red, far-red, and blue light. This indicated that ZIM functioned as a negative regulator in the signal transduction pathway after convergence of photoreceptor-mediated light signals. The hypocotyl and petiole elongation in ZIM-ox was inhibited by brassinazole, a brassinosteroid biosynthesis inhibitor, which indicated that the elongation required brassinosteroids. These results suggest that ZIM is a regulator of photomorphogenesis via brassinosteroids. We are analyzing microarray data from ZIM-ox to identify genes responsible for elongation.
