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 pathogen Ralstonia solanacearum have the ability to restrict bacterial movement in the plant. Inducible vascular cell wall reinforcements seem to play a key role in confining R. solanacearum into the xylem vasculature of resistant tomato. However, the type of compounds involved in such vascular physico-chemical barriers remain understudied, while being a key component of resistance. Here we use a combination of histological and live-imaging techniques, together with spectroscopy and gene expression analysis to understand the nature of R. solanacearum-induced formation of vascular coatings in resistant tomato. We describe that resistant tomato specifically responds to infection by assembling a vascular structural barrier formed by a ligno-suberin coating and tyramine-derived hydroxycinnamic acid amides. Further, we show that overexpressing genes of the ligno-suberin pathway in a commercial susceptible variety of tomato restricts R. solanacearum movement inside the plant and slows disease progression, enhancing resistance to the pathogen. We propose that the induced barrier in resistant plants does not only restrict the movement of the pathogen, but may also prevent cell wall degradation by the pathogen and confer anti-microbial properties, effectively contributing to resistance.

Keywords: Ralstonia solanacearum; HCAAs; bacterial wilt; feruloyltyramine; lignin; suberin; tomato; vascular coating.