Shoot development is regulated by specific gene expression programs depending on the interplay between transcription factors and growth hormones that function in specific domains of the meristem and lateral organs. Functional relationship between different regulators is not clearly established. In the May issue of Plant Physiology (2007) we have shown that Wuschel-like Homeobox3 and YABBY3 are coexpressed in the leaf primordia and young leaves, and that WOX3 functions as a transcriptional repressor of YAB3. Overexpression of WOX3 or downregulation of YAB3 induced ectopic expression of Knotted 1-like homeobox1 genes in leaves and consequently produced a phenotype similar to plants ectopically expressing KNOXI genes. In a parallel work published in the same issue, we have shown that another YABBY gene, YAB1, which is expressed in the same domains as YAB3 or WOX3, binds to the gibberellic acid responsive element and is involved in the feedback regulation of gibberellin biosynthesis. Our study demonstrates that rice YABBY genes are involved in two pathways to control cell division and differentiation during leaf formation and growth and establishes a rice shoot developmental regulatory hierarchy involving WOX3, YAB3, KNOX1 and gibberellin.
Keywords: KNOX1; Wuschel-like homeobox; YABBY; feedback regulation and repression; gibberellin; meristem; rice; shoot.