YABBY genes in plants

Abstract

YABBY genes are a new class of genes that control plant development, probably by transcriptional regulation. At least six YABBY genes exist in Arabidopsis and two in rice. The mutant phenotypes and expression patterns of two family members, FILAMENTOUS FLOWER (FIL)1 and CRABS CLAW (CRC)2,3, suggest that this family plays important roles in plant development. FIL is expressed in all lateral organs (cotyledons, leaves, floral meristems and the floral organs) early in development, but later becomes localized to the abaxial side (the side that faces away from the shoot apex). However, plants that are mutant for FIL show defects only in the floral meristems and flowers, suggesting that this gene is redundant in the leaf – possibly as well as the closely related YAB3. CRC is expressed in the carpels, where it controls growth independently of AGAMOUS (the MADS box gene providing the ‘C’ function in the ABC model of floral patterning) and SPATULA, a gene described in the same paper2. CRC is also essential for nectary development, in which it is expressed throughout development. YABBY genes contain a zinc finger that might be involved in DNA binding or protein–protein interactions, and a helix–loop–helix motif that resembles the first two helices of the HMG box (the DNA-binding domain of a large eukaryotic gene family). These features suggest that YABBY genes are transcriptional regulators. This is supported by the nuclear localization of FIL. A review accompanying the FIL paper4 suggests that the YABBY genes have a role in specifing the abaxial domain of lateral organs. Data to support a role in dorso–ventral patterning isn’t yet available, but the expression patterns and the mutant phenotypes of this family described in these papers suggest that the ‘yabbies’ will be ones to watch.