# ELONGATED HYPOCOTYL5 Regulates Resistance to Root-Knot Nematode by Modulating Antioxidant System and Jasmonic Acid in Cucumis sativus

## TL;DR

This study shows that the HY5 gene in cucumbers helps protect against root-knot nematodes by boosting antioxidant and hormone defenses.

## Contribution

The study reveals a novel role of CsHY5 in cucumber resistance to root-knot nematodes through antioxidant and jasmonic acid pathways.

## Key findings

- The hy5 mutant had more nematodes and galls, showing increased susceptibility to RKNs.
- CsHY5 influences jasmonic acid and antioxidant enzyme activity in response to RKN infection.
- Key genes like CsAOC, CsAOS, and CsPOD were induced in wild-type but not in the hy5 mutant.

## Abstract

Root-knot nematodes (RKNs), specifically Meloidogyne incognita, are notoriously difficult to eliminate as endophytic nematodes, and cause severe damage to various plants. Cucumber (Cucumis sativus), which is a cash crop widely grown across the world, is often infected by RKNs. ELONGATED HYPOCOTYL5 (HY5), a member of the bZIP transcription factor family, plays a vital role in hormone, nutrient, abiotic stress, biotic stress, and oxygen species (ROS) signaling pathways. However, the involvement of HY5 in the defense against RKNs has rarely been reported. The present study initially explored the response of CsHY5 to RKNs. The results indicated that the hy5 mutant had a higher number of nematodes and galls in the root system and exhibited a higher susceptibility to RKNs compared with the wild type (WT). Particularly, the root-knot nematodes in hy5 plants completed their life cycle more quickly and produced more eggs. The activities of defense-related hormones and antioxidant enzymes were measured, and the results indicated that JA, jasmonoyl-isoleucine (JA-Ile), abscisic acid (ABA), peroxidase (POD), and ascorbate peroxidase (APX) were significantly elevated in the wild type, but were not induced or decreased in the mutant. Through transcriptome sequencing analysis and quantitative real-time PCR (qRT-PCR), it was found that when RKNs infect plants, the key genes of jasmonic acid (JA) synthesis, CsAOC and CsAOS, as well as the key gene of the antioxidant system, CsPOD, were all significantly induced. Nevertheless, this induction effect disappeared in the hy5 mutant. Generally, CsHY5 plays a role in the response of cucumber to RKNs, and its deletion increases the sensitivity of cucumber to RKNs. These results suggest that CsHY5 may affect the resistance of cucumber to RKNs by affecting antioxidant enzyme activities and hormone content.