INDEHISCENT and SPATULA interact to specify carpel and valve margin tissue and thus promote seed dispersal in Arabidopsis.

Structural organization of organs in multicellular organisms occurs through intricate patterning mechanisms that often involve complex interactions between transcription factors in regulatory networks. For example, INDEHISCENT (IND), a basic helix-loop-helix (bHLH) transcription factor, specifies formation of the narrow stripes of valve margin tissue, where Arabidopsis thaliana fruits open on maturity. Another bHLH transcription factor, SPATULA (SPT), is required for reproductive tissue development from carpel margins in the Arabidopsis gynoecium before fertilization.

SPATULA and ALCATRAZ, are partially redundant, functionally diverging bHLH genes required for Arabidopsis gynoecium and fruit development.

The Arabidopsis gynoecium is a complex organ that facilitates fertilization, later developing into a dehiscent silique that protects seeds until their dispersal. Identifying genes important for development is often hampered by functional redundancy. We report unequal redundancy between two closely related genes, SPATULA (SPT) and ALCATRAZ (ALC), revealing previously unknown developmental roles for each.

Functional domains of SPATULA, a bHLH transcription factor involved in carpel and fruit development in Arabidopsis.

The SPATULA (SPT) gene is involved in generating the septum, style and stigma: specialized tissues that arise from carpel margins. By matching sequences within the extended bHLH region of AtSPT across species databases, twelve orthologues were identified in eudicots, rice and a gymnosperm. Two conserved structural domains were revealed in addition to the bHLH region: an amphipathic helix and an acidic domain.