LAUSR

Breadfruit (Artocarpus altilis) is a traditional staple tree crop in the Oceania. Susceptibility to tropical windstorm damage has driven an interest in developing breadfruit with dwarf stature. Gibberellin (GA) is one of the most important determinants of plant height and DELLA proteins are repressors of GA signalling pathway. As a first step toward understanding the molecular mechanism of growth regulation in the species, we isolated two full-length DELLA cDNAs, AaDELLA1 and AaDELLA2 from breadfruit. Sequence analysis indicated the deduced proteins encoded by these AaDELLAs bear all the hallmarks of functional DELLA of other species. Transcripts of AaDELLA1 and AaDELLA2 were detected in all plant organs, but the expression was much lower in flowers and fruits. AaDELLA1 showed predominantly higher expression in roots, but AaDELLA2 displayed higher expression in stems and leaves. Expression of both AaDELLAs was not significantly changed by exogenous GA3 treatment. Under paclobutrazol treatment, the expression of AaDELLA2 was up-regulated, but the expression of AaDELLA1 was not changed significantly. Treatments of high salinity up-regulated the expression levels of both AaDELLA1 and AaDELLA2. Treatment of drought stress increased the expression of AaDELLA2, but not that of AaDELLA1. The function of AaDELLAs is discussed with particular reference to their role in stem elongation and the opportunities of breadfruit dwarfing.