Identification and characterization of MeERF genes and their targets in pathogen response by cassava (Manihot esculenta)

Cassava, Manihot esculenta Crantz (Me), is a major dietary source of calories for over 700 million people in tropical regions. The production of cassava is constantly threatened by cassava bacterial blight (CBB), caused by Xanthomonas axonopodis pv. manihotis (Xam). The gene resources for CBB-resistant breeding of cassava are limited. In model plant species, ethylene response factors play important roles in response to pathogen infection. In this study, cassava ethylene response factors (MeERFs) were identified and characterized as the first step in studying their potential for CBB-resistant breeding of cassava. In the cassava genome 155 MeERFs were identified, of which 23 were induced by Xam infection. The promoter regions of 204 genes harbored GCC-box that had the potential to interact with MeERFs. Using 37 transcriptomes derived from Xam infection treatment, four gene co-expression modules for the MeERFs and GCC-box containing genes were constructed. Six MeERFs were associated with two GCC-box containing genes: transcription initiation factor TFIIE subunit beta (MeTFIIE), and histone-lysine N-methyltransferase ASHR1 (MeASHR1). Dual-luciferase reporter assays showed that MeERF10 and MeERF58 positively regulated MeTFIIE; MeERF137 negatively regulated MeTFIIE; MeERF10 and MeERF137 positively regulated MeASHR1; and MeERF35 negatively regulated MeASHR1. The four MeERFs may mediate pathogen response by regulating the expression of the two GCC-box containing genes.