Poster: Vegetative Development

Abs # 447: The role of LOB-domain genes in leaf development

Presenter:	Springer, Patricia S., patricia.springer@ucr.edu
Authors	Springer, Patricia S. (A)   Lin, Wan-ching  (A)   Shuai, Bin  (A)
Affiliations:	(A): University of California - Riverside

The normal development of lateral organs of the shoot requires the simultaneous repression of meristem-specific genes and the activation of organ-specific genes. This process must therefore involve communication between the shoot apical meristem (SAM) and initiating lateral organ primordia. The Arabidopsis LATERAL ORGAN BOUNDARIES (LOB) gene is expressed in a group of cells between the SAM and lateral organs in a pattern suggestive of a role in communication between the two domains. Consistent with this idea, LOB expression is regulated by KNOX genes expressed in the SAM and by genes such as ASYMMETRIC LEAVES1 that are expressed in lateral organ primordia. LOB encodes a novel, plant-specific protein that defines a large gene family in Arabidopsis. Loss-of-function mutations in LOB do not cause a conspicuous phenotype, so as yet, the biological role of LOB is unknown. ASYMMETRIC LEAVES2 (AS2), a gene that is required both for the development of normal leaf shape and for the repression of KNOX genes in the leaf, encodes a LOB-domain protein that is closely related to LOB. Transgenic plants that ubiquitously express AS2 under the control of the 35S promoter produce cotyledons and leaves that curl upward (toward the adaxial side), develop outgrowths on the abaxial surface, and undergo reduced blade expansion. 35S-AS2 leaves have defects in vascular patterning and exhibit abnormal abaxial-adaxial polarity. KNOX genes are also down-regulated in 35S-AS2 plants. Over-expression of the related gene LOB DOMAIN36 causes a similar spectrum of phenotypes, including down-regulation of KNOX genes. These data suggest that a sub-class of LOB-DOMAIN genes function to regulate both KNOX gene expression and adaxial-abaxial polarity.