SPATULA, a gene that controls development of carpel margin tissues in Arabidopsis, encodes a bHLH protein

Studies involving mutants of the gene SPATULA indicate that it promotes the growth of carpel margins and of pollen tract tissues derived from them, We show that it encodes a new member of the basic-helix-loop-helix family of transcription factors. SPATULA is expressed in marginal and pollen tract ti ssues throughout their development confirming its role in regulating their growth. It is also expressed in many other tissues where it may act redunda ntly to control growth, including the peripheral zone of the shoot epical m eristem, and specific tissues within leaves, petals, stamens and roots. Exp ression in the stomium, funiculus and valve dehiscence zone indicates an ad ditional role in abscission, SPATULA expression does not require the functi on of the other carpel development genes CRABS CLAW and AGAMOUS, although i ts expression is repressed in first whorl organs by the A function gene APE TALA2, Further, we have shown that disruptions to gynoecial pattern formati on seen in ettin mutants can largely be attributed to ectopic SPATULA actio n. ETTIN's role seems to be to negatively regulate SPATULA expression in ab axial regions of the developing gynoecium, SPATULA is the first basic-helix -loop-helix gene in plants known to play a role in floral organogenesis.