S16 - Session P2 - Control of fruitlet abscission in mango

Authors: Avinash Chandra Rai, Eyal Halon, Hanita Zemach, Adi Faigenboim, Sonia Philosoph-Hadas, Shimon Meir, Yuval Cohen, Vered Irihimovitch *

In mango ( Mangifera indica L.), fruitlet abscission limits productivity. Fruitlet abscission initiates with a decrease in polar auxin transport through the abscission zone (AZ), triggered by ethylene. The secreted IDA (INFLORESCENCE DEFICIENT IN ABSCISSION) peptide acts as key component controlling abscission events in Arabidopsis. Recent reports suggest that IDA-like (IDL) peptides may assume similar roles in fruit trees. In a current study, we aimed to determine whether IDA-like genes assume conserved roles in affecting mango fruitlet drop. Towards this end, we isolated two IDA/IDL-like encoding genes (termed MiIDA1 and MiIDA2 ). We used mango fruitlet explants and fruitlet-bearing trees, in which fruitlet drop was induced by ethephon, and monitored MiIDA1 and MiIDA2 expression patterns, together with that of different ethylene-related and cell wall-modifying genes, in control and ethephon-treated fruitlet AZs. We also examined the ectopic expression of MiIDA1 and MiIDA2 in Arabidopsis, and their capacity to repair the abscission deficiency of an Atida mutant. Our data provide different evidences supporting the conserved functions of both MiIDA1 and MiIDA2 in regulating mango fruitlet drop, following ethephon-mediated induction. To further study the mechanisms regulating mango fruitlet abscission, we conducted a transcriptome analysis, using control and ethephon-treated fruitlet AZs. Among findings, we observed changes in the expression of genes encoding for hormones (ethylene, auxin and ABA), and increased expression of MiIDA1 , MiIDA2 and of distinct cell wall degrading genes. Interestingly, we also observed upregulation of genes encoding for precursors of phytosulfokines (PSKs), in the treated AZs. PSKs are small peptide hormones, recently suggested to act as new players affecting drought-induced flower abscission in tomato . Whether they assume roles in mango fruitlet abscission, remains to be established. Understanding of the mechanisms regulating mango fruitlet drop may assist in the development of methods to mitigate this problem, and provide candidate genes for biotechnological applications .