GLR36T807I Mutation of Casuarina equisetifoli Is Associated With a Decreased JA Response to Insect Feeding by Lymantria xylina

Lymantria xylina is the most important defoliator, damaging the effective coastal windbreak tree species Casuarina equisetifolia . However, the underlying genetic mechanisms through which C . equisetifolia responds to L . xylina attacks remain unknown. Here, we compared the transcriptional, phytohormone and metabolic differences between susceptible (S) and resistant (R) C . equisetifolia cultivars in response to L . xylina feeding. The main L . xylina -induced resistance in C . equisetifolia was a jasmonate (JA) response and JA synthesis was highly induced by L . xylina feeding at both the transcriptional and metabolic levels, thus promoting flavonoid accumulation. The JA response was highly activated by L . xylina feeding on the R but not in the S cultivar, although the JA signalling pathway was intact in both cultivars. We found a single amino acid mutation in the homologues of glutamate receptor-like protein 3.6 (CeGLR3.6 T807I ) in the S cultivar. Compared with the GLR3.6 homologues in the R cultivar, phosphorylation of CeGLR3.6 T807I was not induced by insect feeding, leading to a decreased JA response in the S cultivar. Collectively, this study provides new insights into the function of CeGLR3.6 in regulating the JA response of C . equisetifolia to L . xylina feeding.