Characterization of the sugarcane MYC gene family and the negative regulatory role of ShMYC4 in response to pathogen stress

As a core regulator of the jasmonic acid (JA) signaling pathway, myelocytomatosis (MYC) transcription factors play a significant role in plant stress responses. However, there are currently no report on the MYC genes in sugarcane (Saccharum spp.), an important sugar and energy crop worldwide. Here, 23 SsMYC genes in Saccharum spontaneum, 3 ShMYC genes in Saccharum spp. hybrid R570 and 8 SbMYC genes in Sorghum bicolor were identified and classified into four groups (A-1, A-2, B, and C). Synteny analysis showed a close relationship among the MYC genes of S. spontaneum, R570, and S. bicolor. The cis-regulatory elements (CREs) in the promoter regions of the MYC genes were related to light, plant growth/development, hormones, and stress. RNA sequencing and real-time quantitative polymerase chain reaction analysis demonstrated that MYC genes were differentially expressed in sugarcane tissues and under Sporisorium scitamineum stress. A novel ShMYC4 gene was cloned from Saccharum spp. hybrid ROC22 and validated to be a nuclear-localized group A-1 member without transcriptional self-activating activity. The decreased transcripts of ShMYC4 in six different sugarcane cultivars may have been associated with its negative response to S. scitamineum. Additionally, transient expression showed that ShMYC4 negatively regulated the defense response of Nicotiana benthamiana to Ralstonia solanacearum and Fusarium solani var. coeruleum by mediating the hypersensitive response, salicylic acid, JA and ethylene pathways. This study provided comprehensive information for the MYC gene family in sugarcane, which should be helpful for functional characterization of sugarcane MYC genes in the future.