Abstract
The ASYMMETRIC LEAVES2 (AS2) gene is required for the generation of the flat and symmetrical shape of the leaf lamina in Arabidopsis. AS2 encodes a plant-specific protein with an AS2/LATERAL ORGAN BOUNDARIES (AS2/LOB) domain that includes a cysteine repeat, a conserved single glycine residue and a leucine-zipper-like sequence in its amino-terminal half. The Arabidopsis genome contains 42 genes, including AS2, that encode proteins with an AS2/LOB domain in their amino-terminal halves, and these genes constitute the AS2/LOB gene family. In the present study, we cloned and characterized cDNAs that covered the putative coding regions of all members of this family, and investigated patterns of transcription systematically in Arabidopsis plants. Comparisons among amino acid sequences that had been deduced from the cloned cDNAs revealed eight groups of genes, with two or three members each, and high degrees of identity among entire amino acid sequences, suggesting that some members of the AS2/LOB family might have redundant function(s). Moreover, no member of the family exhibited significant similarity, in terms of the deduced amino acid sequence of the carboxy-terminal half, to AS2. Results of domain swapping between AS2 and other members of the family showed that the AS2/LOB domain of AS2 cannot be functionally replaced by those of other members of the family, and that only a few dissimilarities among respective amino acid residues of the AS2/LOB domain of AS2 and those of other members are important for the specific functions of AS2.
Highlights
Our results showed that the ASYMMETRIC LEAVES2 (AS2)/ LATERAL ORGAN BOUNDARIES (LOB) domains of AS2-like/LOB domain (ASL/LBD) proteins cannot replace that of AS2 during leaf development, even if only a few amino acid residues differ between the AS2/LATERAL ORGAN BOUNDARIES (AS2/LOB) domain of AS2
The results of our analysis of the cDNA for ASL22/LBD31 showed that the splice acceptor site of this gene was located 15 bp upstream of the site that had been predicted by TIGR analysis of the Arabidopsis genome, to yield five additional amino acid residues in the leucine-zipper-like motif in the AS2/LOB domain
We obtained 35, 14, 14, 12, 16, 15, 22 and 15 lines of as2-1/ SWAP1, as2-1/SWAP2, as2-1/SWAP3, as2-1/SWAP4, as2-1/ SWAP15, as2-1/SWAP18, as2-1/SWAP23 and as2-1/SWAP37 transgenic plants, respectively. None of these SWAP lines showed any evidence of complementation (Figure 5e,f,h), with the exception that the leaves, which were reduced in length in the proximal–distal direction in as2-1 plants, were slightly closer to the wild-type length in 17 out of the 35 as21/SWAP1 transgenic plants (Figure 5e). These results suggest that the AS2/LOB domains of ASL/LBD proteins other than AS2 cannot functionally replace the AS2/LOB domain of AS2 in leaf development
Summary
Loss-of-function mutations in the ASYMMETRIC LEAVES2 (AS2) gene in Arabidopsis result in various defects in leaf development, such as the formation of asymmetrically lobed and downwardly curled leaves, the formation of leaflet-like structures from petioles, the generation of an abnormal venation system, and the ectopic expression of class 1 KNOX genes in the leaves (Redei and Hirono, 1964; Re-use of this article is permitted in accordance with the Creative Commons Deed, Attribution 2.5, which does not permit commercial exploitation.a 2009 The Authors Journal compilation a 2009 Blackwell Publishing LtdOri et al, 2000; Semiarti et al, 2001; Byrne et al, 2002; Xu et al, 2003). The AS2 gene encodes a plant-specific protein with a domain that consists of a cysteine repeat (the C-motif), a conserved glycine residue and a leucine-zipper-like sequence in its amino-terminal (N-terminal) half (Iwakawa et al, 2002; Machida et al, 2003). This domain has been designated the AS2 domain or the LATERAL ORGAN BOUNDARIES (LOB) domain (Iwakawa et al, 2002; Shuai et al, 2002; hereafter designated as the AS2/LOB domain). As, in which there is a mutation in the region encoding the carboxy-terminal (C-terminal) half of AS2, causes the typical mutant phenotype, it is clear that the C-terminal half plays a role in the functioning of AS2
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