Metabolome and Transcriptome Analysis of Sulfur-Induced Kiwifruit Stem Laccase Gene Involved in Syringyl Lignin Synthesis against Bacterial Canker

Kiwifruit
canker is caused by Pseudomonas syringae pv. actinidiae and is one of the most destructive
diseases of kiwifruit worldwide. Sulfur can improve the deposit of
lignin in kiwifruit stems and induce disease resistance, but the action
mechanism at the molecular level remains unclear. This omics-based
study revealed that sulfur-induced S lignin synthesis contributes
to disease resistance. Histological staining verified sulfur-enhanced
total lignin deposition in kiwifruit stems. High-performance liquid
chromatography and confocal Raman microscopy showed that sulfur-activated
S lignin was mainly deposited in the cell corner. Metabolome and transcriptome
analysis revealed that the levels of phenylpropanoid pathway S lignin
precursors sinapic acid and sinapyl alcohol were significantly increased
and 16 laccase genes were upregulated. Sulfur-induced resistance defense
promoted elevated laccase activity by activating the laccase genes,
participating in sinapic acid and sinapyl alcohol substance synthesis,
and ultimately polymerizing S lignin at cell corner against kiwifruit
canker disease.