Molecular insights into avocado grafting: the role of chitinase-like genes

Grafting is an agricultural technique used widely to increase yield, enhance stress tolerance, and improve disease resistance. The valuable avocado (Persea americana Mill.) rootstock VC801 provides these benefits but exhibits poor rooting capacity, necessitating a labor-intensive double-grafting procedure that involves a nursing seedling and etiolation. In this study, we found that grafting of the "Hass" cultivar onto VC801 was successful only when the rootstocks were etiolated; by contrast, grafts on green rootstocks largely failed, indicating physiological incompatibility. Transcriptome analysis revealed that graft success was associated with differential expression of cell wall-related genes, among which chitinase-like transcripts were particularly prominent. Repeated RT-qPCR validation highlighted the Ctg0022 chitinase-like transcript. The Arabidopsis (Arabidopsis thaliana) mutant ctl1-1, which is defective in a homologous chitinase-like gene, displays graft incompatibility. Remarkably, heterologous expression of Ctg0022, particularly in the rootstock, restored graft compatibility in these mutants. Complementary analyses, including inhibitor treatments, histology, microscopy, and gene expression profiling, indicated that Ctg0022 modulates cell wall remodeling by influencing cellulose, lignin, and pectin composition. Fluorescence lifetime imaging further showed aberrant cell wall assemblies and impaired cell division and cell adhesion at the graft interface of ctl1-1 mutants; these were restored in Ctg0022-expressing plants. Together, our findings demonstrate that the fine-tuned expression of avocado chitinase-like gene Ctg0022 can promote successful graft union formation, highlighting a conserved role in cell wall remodeling during grafting.