Analysis of the function of the AS2 gene family in development of leaves

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The ASYMMETRIC LEAVES1 (AS1) and the ASYMMETRIC LEAVES2 (AS2) genes of Arabidopsis thaliana are involved in the establishment of the leaf venation system, which includes the prominent midvein, as well as in the development of a symmetric flat lamina. The genes might also function in maintaining leaf cells in a developmentally determinate state, probably by repressing expression of class 1 knox homeobox genes. The AS2 gene encodes a protein with a novel domain (AS2 domain) that contains cysteine repeats (C-motif), conserved glycine, and a leucine-zipper-like sequence. Arabidopsis genome contains 42 putative genes (AS2 and ASL1-41) that potentially encode th e AS2 domain. The AS2, ASL1, ASL2, ASL3 and ASL4 proteins include most amino acid residues in t he AS2 domain that are conserved among these proteins. Loss-of-function mutations in ASI or AS2 generated downwardly curled leaves, although overexpression of AS2 resulted in upwardly curled leaves in the presence of the AS1. The transgenic plants that overexpressed ASL1 also showed upwardly curled leaves. (1) To understand the functions of the AS2 domain in the AS2 and ASL1-4 in the leaf development in Arabidopsis, we have isolated loss-of-function mutations in ASL1, ASL2 and ASL3 genes. As a single mutation in ASL1 and ASL3 resulted in no phenotype at least in vegetative stage, genetic analysis using the as1, as2, by and asls mutants is in progress. (2) The stable transformant contained GFP-fused AS2 showed the fluorescence signals in nuclei. The C-motif in AS2 was required for the nuclear localization. When the fusion constructs of ASL1::GFP and ASL3::GFP were introduced into onion epidermal cells, fluorescence signals were detected mainly in nuclei. These proteins may be nuclear factors that regulate expression of some genes such as class 1 knox genes.