Transcriptomics of Sugarcane Plants Colonized by the Bacterial Pathogen Leifsonia xyli subsp. xyli Indicates Major Interference in the Expression of Cell Cycle and Hormone Signaling Genes

Ratoon stunting disease (RSD) is one of the most important diseases of sugarcane worldwide; however, little is known about the biology of the interaction between its causal agent, the fastidious bacterium Leifsonia xyli subsp. xyli (Lxx), and the host plant. This study compared gene expression levels of plants of the sugarcane variety SP80-3280 inoculated or not with Lxx. Plants were grown in the greenhouse and inoculated 60 days after planting. Control plants were mock-inoculated with sterile culture medium. Thirty and sixty days after inoculation, bacterial titers in tissue of the leaf whorl were determined by qPCR. Transcription profiles were analyzed by microarray hybridization (SUCEST-FUN chip). Bacterial titers differed between plants mock-inoculated and inoculated with Lxx and this correlated with shifts in transcript levels. A total of 106 genes, distributed in 17 functional categories were differentially expressed 30 days after inoculation, the majority (54 genes) being classified as of unknown function. However, the second largest category (20 genes) comprised genes controlling cell cycle. The expression of all members of this category was repressed in inoculated plants. Sixty days after inoculation, 152 genes were identified as differentially expressed and grouped in additional functional categories with respect to 30 days, such as resistance to pathogens and protein metabolism. Moreover, there was an increase in the number of genes of the hormone biosynthesis and signal transduction categories (27 genes). Changes in gene expression are consistent with the major symptoms of RSD, i.e., stunted growth, shortening of the internodes and thinner stalks.