Functional divergence of CAD-like family genes in Saccharum complex under biotic and abiotic stress.

A total of 54 genes of membrane attack complex/perforin (MACPF) superfamily were identified in Saccharum complex and function divergence among SsaCAD-like genes were present in plant against stressors. The membrane attack complex/perforin (MACPF) superfamily belongs to pore-forming proteins involving in innate and adaptive immunity in eukaryotes. The constitutively activated cell death (CAD) proteins contained the MACPF domain participate in plant defense responses under adverse conditions. However, the characteristics and functions of CAD-like genes in sugarcane are still poorly understood. In this study, 54 CAD-like genes were identified in three genomes from Saccharum complex including two clones (Np-X and AP85-441) of Saccharum spontaneum and a clone (Yunnan2009-3) of Erianthus rufipilus. All CAD-like genes were categorized into five phylogenetic groups (I-V). Various cis-acting elements related to stress responses, such as phytohormone response elements, were found in promoter regions. Transcriptome and RT-qPCR analysis demonstrated these genes possessing diverse expression profiles. The SsaCAD1-like1 gene was upregulated in sugarcane cultivars after cold treatment and infection by Xanthomonas albilineans (Xa) causing leaf scald. Meanwhile, this gene was downregulated under drought and ABA treatments but was upregulated and then downregulated across time-points of SA treatment. The SsaCAD4-like1 gene was downregulated under five abiotic stressors. Expression levels of two alleles (SsaCAD2-like1/2) were significantly decreased under all abiotic stressors except for salinity treatment. Similar expression patterns of three alleles (SsaCAD3-like1/2/4) were found under abiotic stress. The SsaCAD1-like1 exhibited a negative role but SsaCAD3-like2/4 acted as positive roles in transgenic Arabidopsis lines against bacterial pathogen infection. Our results provide novel gene resources for developing disease-resistant cultivars in sugarcane.