MebZIPs And MeDELLAs Positively Regulate Cassava Disease Resistance Against Cassava Bacterial Blight

Cassava is one kind of tropical and energy crops,which is very important in our life and production.The output and the quality of cassava often affected by various diseases and stresses.Therefore,it is helpful to improve the resistance of cassava by studying the relevant genes which may participate in anti-adversity and diseases resistance.Basic domain-leucine zipper transcription factor,one type of conserved gene family,plays an important role in plant development and stress responses.Although 77 MebZIPs have been genome-wide identified in cassava,their in vivo roles remain unknown.In this study,we analyzed the expression pattern and the function of three MebZIPs(MebZIP3,MebZIP5 and MebZIP9)in response to pathogen infection.Gene expression analysis indicated that MebZIP3,MebZIP5 and MebZIP9 were commonly regulated by flg22,Xam,SA,and H2O2.Subcellular localization analysis showed that three MebZIPs are specifically located in cell nucleus.The yeast transcriptional activation experimental analysis indicated that three MebZIPs had transactivation activity.Through overexpression in tobacco,we found that MebZIP3 and MebZIP5 conferred improved disease resistance against cassava bacterial blight,with more callose depositions and H2O2.On the contrary,MebZIP3-and MebZIP5-silenced plants by virus-induced gene silencing(VIGS)showed disease sensitive phenotype,lower transcript levels of defense-related genes,less callose depositions and H2O2.Gibberellin(GA)is one of the most important plant hormones in plants,and plays an important role in the growth and development of plants as well as various stress reactions.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(MeDELLA1,MeDELLA2,MeDELLA3 and MeDELLA4)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.Taken together,this study highlights the positive role of MebZIP3 and MebZIP5 in disease resistance against cassava bacterial blight,it also is the first study identifying MeDELLAs as positive regulators of disease resistance against cassava bacterial blight,which Provided a reference basis for further utilization in genetic improvement of cassava disease resistance.