Abstract:

Phytophthora blight is a highly destructive soil-borne disease caused by Phytophthora capsici Leonian，which seriously limits pepper production. At present，the molecular mechanism of pepper’s resistance to phytophthora blight is unclear，and the excavation and functional analysis of resistance genes are the basis and prerequisite for phytophthora blight-resistant breeding. A high- generation inbred line ZCM334 of pepper was obtained through preliminary screening，which is immune to physiological races 1，2，and 3 of P. capsici. After inoculation，all plants showed no signs of infection. Transcriptome sequencing and weighted gene co-expression network analysis（WGCNA）were performed on the roots of ZCM334 and susceptible material Early Calwonder at different stages（0，12，24，and 48 h）before and after inoculation. A total of 17 co-expression modules were identified，and 4 modules were screened for significant positive correlation with the resistance to phytophthora blight of ZCM334. The functional enrichment analysis results showed that the target module genes were mainly enriched in metabolic pathways such as plant hormone signal transduction，glycolysis，glucose production，and fatty acid degradation. Correlation analysis was conducted on these four modules to predict 12 hub genes that may be related to pepper resistance to phytophthora blight，including 6 known functional genes（CA06g02420，CA06g08970，CA01g15560，CA09g14900，CA09g14910，and CA09g15310）and 6 new genes（novel.5608，novel.2732，novel.3300，novel.752，novel.2181，and novel.12038），and a gene regulatory network was constructed. qRT-PCR analysis revealed that these 12 hub genes were highly expressed in ZCM334，with the highest expression levels observed 24 or 48 hours after inoculation.

Key words: pepper, Phytophthora capsici, disease resistance, gene co-expression network, gene mining, hub gene, metabolic pathway