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

School of Biological Sciences, Monash University, Melbourne, Vic. 3800, Australia Commonwealth Scientific and Industrial Research Organisation Plant Industry, Canberra, ACT 2601, Australia For correspondence (phone: 61 3 9905 3861; fax 61 3 9905 5613; email
The Arabidopsis gynoecium is a complex organ that facilitates fertilisation, 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. SPT is known to support septum, style and stigma development in the flower, whereas ALC is involved in dehiscence zone development in the fruit. ALC diverged from a SPT-like ancestor following gene duplication coinciding with the At-β polyploidy event. Here we show that ALC is also involved in early gynoecium development, and SPT in later valve margin generation in the silique. Evidence includes the increased severity of early gynoecium disruption, and of later valve margin defects, in spt alc double mutants. In addition, a repressive version of SPT (35S:SPT-SRDX) disrupts both structures. Consistent with redundancy, ALC and SPT expression patterns overlap in these tissues, and the ALC promoter carries two atypical E-box elements identical to one in SPT required for valve margin expression. Further, SPT can heterodimerise with ALC, and 35S:SPT can fully complement dehiscence defects in alc mutants, although 35S:ALC can only partly complement spt gynoecium disruptions, perhaps associated with its sequence simplification. Interactions with FRUITFULL and SHATTERPROOF genes differ somewhat between SPT and ALC, reflecting their different specialisations. These two genes are apparently undergoing subfunctionalisation, with SPT essential for earlier carpel margin tissues, and ALC specialising in later dehiscence zone development.
Unknown Aug. 01, 2011; 0(0); [PUBMED:21801252]
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