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

[EN] 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. Previous studies have therefore assigned the function of SPT to early gynoecium stages and IND to later fruit stages of reproductive development. Here we report that these two transcription factors interact genetically and via protein-protein contact to mediate both gynoecium development and fruit opening. We show that IND directly and positively regulates the expression of SPT, and that spt mutants have partial defects in valve margin formation. Careful analysis of ind mutant gynoecia revealed slight defects in apical tissue formation, and combining mutations in IND and SPT dramatically enhanced both single-mutant phenotypes. Our data show that SPT and IND at least partially mediate their joint functions in gynoecium and fruit development by controlling auxin distribution and suggest that this occurs through cooperative binding to regulatory sequences in downstream target genes.We thank Steve Penfield for spt-11 and spt-12 mutant seeds, Michael Groszmann for the IND genomic clone, 35S:SPT plants, and for useful discussions, Charlie Scutt for critical comments on the manuscript, Nicolas Arnaud for useful discussions, and Martin F. Yanofsky and Kristina Gremski for sharing unpublished observations and useful discussions. We are grateful to Andrew Davis, Sue Bunnewell, and Kim Findlay at the John Innes Centre for assistance with photography, transmission electron microscopy, and scanning electron microscopy and to Dian Guan for constructing the double G-box vector for the yeast one-hybrid experiment. This work was funded by grants from the Biotechnological and Biological Science Research Council (BB/D018005/1 to L. O.), from the Australian Research Council (A19927094 to D. R. S.), from the Spanish Government (BIO2009-09920 to C. F.), and by a Marie Curie Fellowship (MEST-CT-2005-019727 to S.F.).Girin, T.; Paicu, T.; Stephenson, P.; Fuentes, S.; Körner, E.; O'brien, M.; Sorefan, K.... (2011). INDEHISCENT and SPATULA interact to specify carpel and valve margin tissue and thus promote seed dispersal in Arabidopsis. Plant Cell. 23(10):3641-3653. https://doi.org/10.1105/tpc.111.090944S36413653231