Knockdown of SlNL33 accumulates ascorbate, enhances disease and oxidative stress tolerance in tomato (Solanum lycopersicum)

Abstract

Ascorbic acid (AsA) is an antioxidant that plays an important role in scavenging reactive oxygen species and enhancing disease resistance in plants. In tomato, unlike biosynthesis pathway, the regulatory network of ascorbate remains largely unclear. Here, we reported the isolation and characterization of SlNL33, the gene that encodes an NL type NBS-LRR resistance protein by candidate gene-based association study. Knockdown of SlNL3 by RNA interference in tomato (Solanum lycopersicum cv. Ailsa Craig) increased AsA level in both fruit (~ 1.3 fold) and leaf (more than twofold). qRT–PCR analysis revealed that elevated expression of several structural genes involved in ascorbate biosynthesis including GMP4, GME1, GGP1, GalDH, GLDH, MIOX, MDHAR, and DHAR, may contribute to the ascorbate accumulation in SlNL33 RNAi lines compared with wild-type. Furthermore, the SlNL33-RNAi transgenic lines showed enhanced tolerance to oxidative stress by methyl viologen and gray mold infection by Botrytis cinerea respectively, as compared to control plants. Taken together, the present findings revealed that SlNL33 was the first identified NBS-LRR gene that plays a negative role in the AsA accumulation as well as biotic and abiotic stress tolerance in tomato.