A role for the rice homeobox gene Oshox1 in provascular cell fate commitment

The vascular tissues of plants form a network of interconnected cell files throughout the plant body. The transition from a genetically totipotent mer istematic precursor to different stages of a committed procambial cell, and its subsequent differentiation into a mature vascular element, involves de velopmental events whose molecular nature is still mostly unknown. The rice protein Oshox1 is a member of the homeodomain leucine zipper family of tra nscription factors. Here we show that the strikingly precise onset of Oshox 1 gene expression marks critical, early stages of provascular ontogenesis i n which the developmental fate of procambial cells is specified but not yet stably determined. This suggests that the Oshox1 gene may be involved in t he establishment of the conditions required to restrict the developmental p otential of procambial cells. In support of this hypothesis, ectopic expres sion of Oshox1 in provascular cells that normally do not yet express this g ene results in anticipation of procambial cell fate commitment, eventually culminating in premature vascular differentiation. Oshox1 represents the fi rst example of a transcription factor whose function can be linked to speci fication events mediating provascular cell fate commitment.