Abstract
Sugarcane (Saccharum spp. hybrids) is a major source of sugar and renewable bioenergy crop worldwide and suffers serious yield losses due to many pathogen infections. Leaf scald caused by Xanthomonas albilineans is a major bacterial disease of sugarcane in most sugarcane-planting countries. The molecular mechanisms of resistance to leaf scald in this plant are, however, still unclear. We performed a comparative transcriptome analysis between resistant (LCP 85-384) and susceptible (ROC20) sugarcane cultivars infected by X. albilineans using the RNA-seq platform. 24 cDNA libraries were generated with RNA isolated at four time points (0, 24, 48, and 72 h post inoculation) from the two cultivars with three biological replicates. A total of 105,783 differentially expressed genes (DEGs) were identified in both cultivars and the most upregulated and downregulated DEGs were annotated for the processes of the metabolic and single-organism categories, respectively. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis of the 7612 DEGs showed that plant–pathogen interaction, spliceosome, glutathione metabolism, protein processing in endoplasmic reticulum, and plant hormone signal transduction contributed to sugarcane’s response to X. albilineans infection. Subsequently, relative expression levels of ten DEGs determined by quantitative reverse transcription-PCR (qRT-PCR), in addition to RNA-Seq data, indicated that different plant hormone (auxin and ethylene) signal transduction pathways play essential roles in sugarcane infected by X. albilineans. In conclusion, our results provide, for the first time, valuable information regarding the transcriptome changes in sugarcane in response to infection by X. albilineans, which contribute to the understanding of the molecular mechanisms underlying the interactions between sugarcane and this pathogen and provide important clues for further characterization of leaf scald resistance in sugarcane.
Highlights
Sugarcane (Saccharum spp. hybrids) is a major source of sugar and biofuel production worldwide, and it is one of the most valuable cash crops [1]
No leaf scald symptoms were observed at 24 and 48 h post-inoculation, but pencil line streaks that are characteristic of leaf scald were observed at 72 hpi on both cultivars inoculated with X. albilineans (Figure S1A)
We proposed that abscisic acid (ABA) signal transduction pathway may play negative or unimportant role on sugarcane resistance to X. albilineans, as validated by the upregulation of PYL in susceptible cultivar ROC20 but no significant change in the transcripts expression of sucrose non-fermenting 1-related protein kinase 2 (SNRK2) gene in two cultivars
Summary
Sugarcane (Saccharum spp. hybrids) is a major source of sugar and biofuel production worldwide, and it is one of the most valuable cash crops [1]. The current commercial cultivars are interspecific hybrids derived from crosses between a few parents belonging to S. officinarum (2n = 80, the noble sugarcane), S. barberi (2n = 111–120, the Indian sugarcanes), S. sinense (2n = 81–124, the Chinese sugarcanes), and the two wild species S. spontaneum (x = 8, 2n = 36–128) and S. robustum (x = 10, 2n = 60–80) [1,3] These crosses resulted in highly polyploid and aneuploid cultivars with 2n = 100–130 chromosomes, hindering the study of genes which regulate most cellular processes in sugarcane [4,5]. The bacterium Xanthomonas albilineans causes a major sugarcane disease called leaf scald [7] This disease results in significant reductions in sugarcane yield and juice quality in susceptible cultivars, preventing their commercial use [8,9]. Despite the importance of the disease, little is known about the molecular processes underlying the sugarcane defense mechanisms in response to X. albilineans infection
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