Overexpression of Sugarcane ScDIR Genes Enhances Drought Tolerance in Nicotiana benthamiana.

Dirigent proteins (DIRs) are known to function in lignin biogenesis and to be involved in stress resistance in plants. However, the sugarcane DIRs have not been functionally characterized. In this study, we investigated the DIR-protein-encoding genes in Saccharum spp. (ScDIR) by screening collections of sugarcane databases, monitoring the responses of these genes to drought stress by real-time quantitative PCR, and identifying their heterologous expression in tobacco. Of the 64 ScDIRs identified, four belonging to the DIR-b/d (ScDIR5 and ScDIR11) and DIR-c (ScDIR7 and ScDIR40) subfamilies showed a significant transcriptional response when subjected to drought stress. ScDIR5, ScDIR7, and ScDIR11 are localized in the cell membrane, whereas ScDIR40 is found in the cell wall. The overexpression of these ScDIR genes in tobacco generally increased the drought tolerance of the transgenic lines, with ScDIR7 conferring the highest degree of drought tolerance. The characterization of the physiological and biochemical indicators (superoxide dismutase, catalase, malondialdehyde, and H2O2) confirmed that the ScDIR-overexpressing lines outperformed the wild type. These results demonstrated that specific ScDIRs in sugarcane respond and contribute to tolerance of drought stress, shedding light on potential means of improving drought tolerance in this crop.

Identification of Gene Modules and Hub Genes Associated with Sporisorium scitamineum Infection Using Weighted Gene Co-Expression Network Analysis.

Sporisorium scitamineum is a biotrophic fungus responsible for sugarcane smut disease. To investigate the key genes involved in S. scitamineum infection, we conducted RNA sequencing of sugarcane sprouts inoculated with S. scitamineum teliospores. A weighted gene co-expression network analysis (WGCNA) showed that two co-expressed gene modules, MEdarkturquoise and MEpurple-containing 66 and 208 genes, respectively-were associated with S. scitamineum infection. The genes in these two modules were further studied using Gene Ontology (GO) enrichment analysis, pathogen-host interaction (PHI) database BLASTp, and small secreted cysteine-rich proteins (SCRPs) prediction. The top ten hub genes in each module were identified using the Cytohubba plugin. The GO enrichment analysis found that endoplasmic reticulum-related and catabolism-related genes were expressed during S. scitamineum infection. A total of 83 genes had homologs in the PHI database, 62 of which correlated with pathogen virulence. A total of 21 proteins had the characteristics of small secreted cysteine-rich proteins (SCRPs), a common source of fungal effectors. The top ten hub genes in each module were identified, and seven were annotated as Mig1-Mig1 protein, glycosyl hydrolase, beta-N-acetylglucosaminidase, secreted chorismate mutase, collagen, mRNA export factor, and pleckstrin homology domain protein, while the remaining three were unknown. Two SCRPs-SPSC_06609 and SPSC_04676-and three proteins-SPSC_01958, SPSC_02155, and SPSC_00940-identified in the PHI database were also among the top ten hub genes in the MEdarkturquoise and MEpurple modules, suggesting that they may play important roles in S. scitamineum infection. A S. scitamineum infection model was postulated based on current findings. These findings help to deepen the current understanding of early events in S. scitamineum infection.