Caracterisation of the Aux/IAA genes family, functional analysis of the Sl-IAA27 gene

Abstract

The phytohormone auxin controls various developmental processes, including apical dominance, tropisms, vascular patterning and fruit set. Auxin metabolism, transport, perception and signaling are mainly studied in the plant model Arabidopsis. To understand the auxin regulation process of fruit development, the tomato plant which is a reference species for Solanaceae and fleshy fruit plants is a good model of study. Aux/IAA genes play a key role in auxin signaling pathway, through their participation to the receptor complex of the hormone and by repressing the activity of ARF type transcription factors. In this work the 25 Sl-IAA family members have been isolated and renamed according to their phylogeny relationship with AtIAAs. Sl-IAA genes display distinctive expression pattern in different tomato organs and tissues, and some of them display differential responses to auxin and ethylene, suggesting that Aux/IAAs may play a role in linking both hormone signaling pathways. To improve knowledge about Aux/IAA function, transgenic tomato plants have been generated. The involvement of Aux/IAAs in notably fruit development was addressed through the characterization of the Sl-IAA27 gene. Its down-regulation in plants lead to altered flower and fruit development with a modified shape of the fruits and reduced volume. Moreover, fertilization capacity was strongly altered by the silencing of Sl-IAA27 resulting in the formation of fruits with reduced seed number. In addition, the reduced expression of Sl- IAA27 leads to a down-regulation of genes involved in chlorophyll biosynthesis triggering reduced leaf chlorophyll accumulation content. These results showed a functional diversity among Sl-IAA family members and underlined the involvement of auxin notably in the regulation of fruit development.