Integrated Analysis of Grapevine Responses to Winter Pruning Reveals Temperature-Associated, Polyphenol-Rich Xylem Occlusions.

Perennial crops are continually wounded throughout cultivation. To limit pathogen infection and tissue dehydration, plants have evolved a range of wound responses that protect damaged tissues. These responses include changes in gene expression and the synthesis of protective compounds such as polyphenols. In addition, plants occlude damaged xylem vessels following wounding and pathogen infection, forming structures such as gels, gums, and tyloses. We explored grapevine responses to pruning. First, we examined the dynamics of xylem vessel occlusion formation at different time points and depths from the wound surface. Second, we characterised transcriptional changes and polyphenol accumulation in response to pruning. Finally, we used Raman microscopy to resolve the spatial chemical composition of xylem vessel occlusions. We found that the winter xylem vessel occlusion response is strongly associated with air temperature. Furthermore, Raman microscopy demonstrated that these occlusions were gel- or gum-like structures enriched in stilbenoids and flavonoids. The accumulation of polyphenols within the occlusions was associated with the up-regulation of stilbene synthase genes and the accumulation and oligomerization of stilbenes. Overall, this study provides an integrated characterisation of perennial woody tissue responses to winter pruning, combining histological, metabolomic, transcriptomic, and spectroscopic approaches, and highlights a potential regulatory role for temperature in xylem vessel occlusion formation and dynamics.