Induced ligno-suberin vascular coating and tyramine-derived hydroxycinnamic acid amides restrict Ralstonia solanacearum colonization in resistant tomato

Abstract

Tomato varieties resistant to the bacterial wilt pathogenRalstonia solanacearumhave theability to restrict bacterial movement in the plant. Inducible vascular cell wall reinforcementsseem to play a key role in confiningR. solanacearuminto the xylem vasculature of resistanttomato. However, the type of compounds involved in such vascular physico-chemical barriersremain understudied, while being a key component of resistance. Here we use a combination of histological and live-imaging techniques, together with spec-troscopy and gene expression analysis to understand the nature ofR. solanacearum-inducedformation of vascular coatings in resistant tomato. We describe that resistant tomato specifically responds to infection by assembling a vascularstructural barrier formed by a ligno-suberin coating and tyramine-derived hydroxycinnamicacid amides. Further, we show that overexpressing genes of the ligno-suberin pathway in acommercial susceptible variety of tomato restrictsR. solanacearummovement inside the plantand slows disease progression, enhancing resistance to the pathogen. We propose that the induced barrier in resistant plants does not only restrict the movementof the pathogen, but may also prevent cell wall degradation by the pathogen and confer anti-microbial properties, effectively contributing to resistance.