Cellular processes that underlie post-mitotic cell expansion must be tightly regulated by overall developmental programmes but how such upstream signals coordinate the timing and extent of cell expansion is not well understood. A recent study suggests that the BIGPETALp (BPEp) gene encoding a basic helix-loop-helix (bHLH) transcription factor might be a part of these signalling cascades since BPEp acts downstream of petal organ identity genes such as APETALA3, PISTILLATA, APETALA1 and SEPALLATA3, and it regulates petal growth by restricting its cell expansion (Szecsi et al. 2006). Plant growth regulators such as auxin, GA and BR are also likely to play a role in transducing such overall developmental cues to individual cells (Belkhadir and Chory 2006). An involvement of some regulatory genes such as ARGOS-
LIKE (ARL) has been suggested in BR-related cell expansion (Hu et al. 2006). In addition, an intriguing link between auxin signalling and ribosome-mediated post-mitotic cell expansion has been revealed by a study on the Arabidopsis and potato EBP1 protein (Horvath 2006).
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