Activation ofCRABS CLAWin the Nectaries and Carpels of Arabidopsis

Abstract

CRABS CLAW (CRC), a member of the YABBY gene family, is required for nectary and carpel development. To further understand CRC regulation in Arabidopsis thaliana, we performed phylogenetic footprinting analyses of 59 upstream regions of CRC orthologs from three Brassicaceae species, including Arabidopsis. Phylogenetic footprinting efficiently identified functionally important regulatory regions (modules), indicating that CRC expression is regulated by a combination of positive and negative regulatory elements in the modules. Within the conserved modules, we identified putative binding sites of LEAFY and MADS box proteins, and functional in vivo analyses revealed their importance for CRC expression. Both expression and genetic studies demonstrate that potential binding sites for MADS box proteins within the conserved regions are functionally significant for the transcriptional regulation of CRC in nectaries. We propose that in wild-type flowers, a combination of floral homeotic gene activities, specifically the B class genes APETALA3 and PISTILLATA and the C class gene AGAMOUS act redundantly with each other and in combination with SEPALLATA genes to activate CRC in the nectaries and carpels. In the absence of B and C class gene activities, other genes such as SHATTERPROOF1/2 can substitute if they are ectopically expressed, as in an A class mutant background (apetala2). These MADS box proteins may provide general floral factors that must work in conjunction with specific factors in the activation of CRC in the nectaries and carpels.

Separate elements of the TERMINAL FLOWER 1 cis-regulatory region integrate pathways to control flowering time and shoot meristem identity

“…A similar promoter structure, with distinct cis-regulatory regions controlling expression in different domains, has also been observed for other developmental regulators, such as the Arabidopsis CRABS CLAW (CRC) or SPATULA (SPT) genes, which, like TFL1, show expression in different domains that changes during development (Lee et al, 2005;Groszmann et al, 2010). This suggests that this type of promoter structure might help achieve a dynamic expression pattern.…”

The spatial expression patterns of DROOPING LEAF orthologs suggest a conserved function in grasses

“…In contrast to these conserved mechanisms, a function in nectary development is specific to CRC in the core eudicot lineage (Bowman and Smyth, 1999;Lee et al, 2005). We have shown here that DL orthologs are involved in carpel specification and midrib formation in the grasses as DL is in rice (Yamaguchi et al, 2004).…”

“…The CRABS CLAW (CRC) gene, an ortholog of DL, is required for nectary development and is partially involved in carpel identity (Alvarez and Smyth, 1999;Bowman and Smyth, 1999;Baum et al, 2001). Promotion of nectary development by CRC orthologs is conserved in eudicots, although the nectary varies in form and originated independently during their evolution (Lee et al, 2005). By contrast, rice DL has no such function, but instead regulates midrib formation in the leaf in rice in addition to carpel specification (Yamaguchi et al, 2004).…”

AWUSCHEL-LIKE HOMEOBOXGene Represses aYABBYGene Expression Required for Rice Leaf Development

“…In Arabidopsis, the function of YABBY genes has been well studied and shown to promote abaxial cell fate in the lateral organs (Bowman, 2000;Sieber et al, 2004;Lee et al, 2005;Meister et al, 2005). Arabidopsis YABBY gene transcripts are detectable in the abaxial domains of lateral organs when primordia emerge and begin to differentiate from the meristem (Bowman, 2000).…”