Systematic study of the stress-responsive Rboh gene family in Nicotiana tabacum: Genome-wide identification, evolution and role in disease resistance.

Plant respiratory burst oxidase homolog (Rboh) gene family encodes the key enzymatic subunits of reactive oxygen species (ROS) production pathways, and play crucial role in plant signaling, development and stress responses. In present work, twenty genes were identified in Nicotiana tabacum Rboh family (NtabRboh) and classified into four phylogenetic groups (I-IV). Fourteen NtabRboh genes were positioned on ten chromosomes (i.e., Ch1, 2, 4, 7-11, 14 and 21), and six scaffolds. Synteny and evolutionary analysis showed that most of the NtabRboh genes have evolved from the genomes of the ancestor species (N. tomentosiformis and N. sylvestris), which afterwards expanded through duplication events. The promoter regions of the NtabRboh genes contained numerous cis-acting regulatory elements for hormones, plant growth, and different biotic and abiotic factors. The NtabRbohF gene transcript comprised target sites for wounding and stress responsive microRNAs: nta-miR166a-d, g and h. The transcript abundance of NtabRboh genes in different tissues reflected their important for plant growth and organ development in tobacco. RT-qPCR-assays demonstrated that the expression of NtabRboh genes are regulated by viral and bacterial pathogens, drought, cold and cadmium stress. The expression levels NtabRbohA, B and C were significantly up-regulated in "black shank and tobacco mosaic virus-inoculated susceptible and transgenic tobacco cultivars, showing that these genes play important roles in disease resistance.