Expression and function of the bHLH genes ALCATRAZ and SPATULA in selected Solanaceae species.

The genetic mechanisms underlying fruit development have been identified in Arabidopsis and have been comparatively studied in tomato as a representative of fleshy fruits. However comparative expression and functional analyses on the bHLH genes downstream the genetic network, ALCATRAZ (ALC) and SPATULA (SPT) which are involved in the formation of the dehiscence zone in Arabidopsis, have not been functionally studied in the Solanaceae. Here we perform detailed expression and functional studies of ALC/SPT homologs in Nicotiana obtusifolia with capsules, and Capsicum annuum and Solanum lycopersicum with berries. In Solanaceae, ALC and SPT genes are expressed in leaves, all floral organs, especially in petal margins, stamens and carpels, however their expression changes during fruit maturation according to the fruit type. Functional analyses show that downregulation of ALC/SPT genes does not have an effect on gynoecium patterning, however, they have acquired opposite roles in petal expansion and have been co-opted in leaf pigmentation in Solanaceae. In addition, ALC/SPT genes repress lignification in time and space during fruit development in Solanaceae. Altogether, some roles of ALC and SPT genes are different between Brassicaceae and Solanaceae. In addition, the paralogs have undergone some subfunctionalization in the former and are mostly redundant in the latter. This article is protected by copyright. All rights reserved.