Comparative transcriptome profiling of resistant and susceptible foxtail millet responses to Sclerospora graminicola infection

Abstract

Abstract Background: Downy mildew of foxtail millet, which is caused by the biotrophic oomycetes Sclerospora graminicola (Sacc.) Schroeter, is one of the most disruptive diseases in foxtail millet. The foxtail millet-S. gramnicola interaction is very poor and largely unexplored. Transcriptome sequencing technology is helpful to reveal the interaction mechanism between foxtail millet and pathogen. Results: In this study, Transmission electron microscopy observation of leaves infected by S. gramnicola showed that the structures of organelles in the host cells were gradually deformed and damaged, or even disappeared from 3- to 7-leaf stages. However, organelles in leaves of resistant varieties were rarely damaged. Meanwhile, the activities of seven cell wall degrading enzymes in resistant and susceptible varieties were also quite different after pathogen induced. Subsequently, we have compared the transcriptional profiles between resistant G1 and high susceptible variety Jingu21 in response to S.graminicola infection at 3, 5, 7 leave stages using the RNA-Seq technology. 473 and 1433 differentially expressed genes (DEGs) were identified in resistance and susceptible varieties, respectively. The pathway analysis of DEGs showed that the highly enriched categories were related to glutathione metabolism, plant hormone signaling, phenylalanine metabolism and cutin, suberine and wax biosynthetic. Some defence-related genes were also revealed in the DEGs, including leucine-rich protein kinase, Ser/Thr protein kinase, peroxidase, cell wall degrading enzymes, laccases and auxin response genes. Equally notable is that the pathyway of starch and sucrose metabolism was enrichment in three infected stages, most of the genes were specifically up-regulated at 5L in susceptible variety, indicating that the expression of genes might be beneficial to and promote the interaction between host and pathogen. Conclusions: Transcriptome sequencing was revealed that host resistance to S. graminicola was likely due to the activation of defense related genes, such as leucine-rich protein kinase, Ser/Thr protein kinase, and alteration of signaling pathways related to hormome. Our study identified pathyway and genes were contributed to the understanding at transcriptomic level of the interaction between foxtail millet and S.graminicola. The results will help to better understand downy mildew of foxtail millet resistance mechanism against S. graminicola.