Comparative Transcriptome Analysis Reveals Differential Gene Expression in Resistant and Susceptible Watermelon Varieties in Response to Meloidogyne incognita

Abstract

M. incognita is a major parasitic plant disease in watermelon production, causing serious economic losses. Although there are many studies on root-knot nematode, the resistance mechanism is still unclear. In this study, in order to fully understand the mechanism of watermelon resistance to root-knot nematode, the relatively strongly resistant ‘Hongzi watermelon’ variety and the susceptible ‘M16’ watermelon variety were used as materials, combined with RNA sequencing (RNA-seq), to analyze the expression abundance of resistant and susceptible varieties at 0, 2, 8 and 15 days post-infection (DPI) by M. incognita. The number of differentially expressed genes (DEGs) in the four comparison groups (A0_B0, A1_B1, A2_B2 and A3_B3) was 3645, 2306, 4449 and 2362, respectively, and there were 835 shared DEGs among them. GO annotation and KEGG pathway enrichment analysis showed that 835 DEGs were mainly involved in phenylpropane biosynthesis and carbon metabolism. Furthermore, lignin-biosynthesis-related genes (4CL (4-coumaric acid-CoA ligase), C3H (coumaric acid 3-hydroxylase), CSE (caffeoyl shikimate esterase), COMT (caffeic acid-O-methyltransferase), CCR (cinnamyl CoA reductase) and PRX (peroxidase)), defense-related proteins (UDP-glucoronosyl/UDP-glucosyl transferase, UGT84A13; salicylic acid binding protein, SABP2) and some transcription factors (TFs) were highlighted, which may be potential candidate genes for further analysis in the infection process of M. incognita. These results suggest that watermelon can achieve resistance to M. incognita by increasing the content of lignin and phenols in root or improving ROS level. These RNA-seq data provide new knowledge for future functional studies and will be helpful to further elucidate the molecular mechanism of resistance to M. incognita in watermelon.

Bacillus velezensis WB induces systemic resistance in watermelon against Fusarium wilt

“…46 It has been reported that overexpression of CCR and 4CL genes in watermelon enhances resistance to Meloidogyne incognita. 44 The results indicated that B. velezensis WB could induce the systemic resistance of watermelon by stimulating phenylpropanoid metabolism in the presence of Fon. In addition, PAL, 4CL, CCR and POD enzymes are involved in lignin biosynthesis in plants.…”

“…demonstrated that the expression of PAL was induced successfully in parsley ( Petroselinum crispum L.) pre‐treatment with benzothiadiazole (BTH) 46 . It has been reported that overexpression of CCR and 4CL genes in watermelon enhances resistance to Meloidogyne incognita 44 . The results indicated that B. velezensis WB could induce the systemic resistance of watermelon by stimulating phenylpropanoid metabolism in the presence of Fon.…”

“…43 Phenylpropanoids are secondary metabolites biosynthesized from phenylalanine in plants, and play an important role in resisting various biotic and abiotic stresses. 44 with Trichoderma asperellum M45 can enhance resistance to Fusarium wilt. 45 Kata et al demonstrated that the expression of PAL was induced successfully in parsley (Petroselinum crispum L.) pre-treatment with benzothiadiazole (BTH).…”

“…In addition, PAL, 4CL, CCR and POD enzymes are involved in lignin biosynthesis in plants. 44 Lignin, a major component of the cell walls of vascular plants, is a first-line defence against the penetration of invasive pathogens. 47 The accumulation of lignin in the WF treatment helps to enhance the mechanical strength of watermelon, thus enhancing the resistance of watermelon to Fon.…”

“…All enzymes mentioned above are involved in phenylpropanoid biosynthesis 43 . Phenylpropanoids are secondary metabolites biosynthesized from phenylalanine in plants, and play an important role in resisting various biotic and abiotic stresses 44 . Zhang et al .…”