Identification and functional analysis of cassava DELLA proteins in plant disease resistance against cassava bacterial blight

Gibberellin (GA) is an essential plant hormone in plant growth and development as well as various stress responses. DELLA proteins are important repressors of GA signal pathway. GA and DELLA have been extensively investigated in several model plants. However, the in vivo roles of GA and DELLA in cassava, one of the most important crops and energy crops in the tropical area, are unknown. In this study, systematic genome-wide analysis identified 4 MeDELLAs in cassava, as evidenced by the evolutionary tree, gene structures and motifs analyses. Gene expression analysis found that 4 MeDELLAs were commonly regulated by flg22 and Xanthomonas axonopodis pv manihotis (Xam). Through overexpression in Nicotiana benthamiana, we found that 4 MeDELLAs conferred improved disease resistance against cassava bacterial blight. Through virus-induced gene silencing (VIGS) in cassava, we found that MeDELLA-silenced plants exhibited decreased disease resistance, with less callose deposition and lower transcript levels of defense-related genes. This is the first study identifying MeDELLAs as positive regulators of disease resistance against cassava bacterial blight.