Cell Wall Dynamics in Haustorial Development of Cuscuta campestris During Parasitism on Differentially Susceptible Hosts

Dodder (<i>Cuscuta campestris</i>) is a parasitic plant that causes severe economic losses to crops such as mung bean (<i>Vigna radiata</i>), although some species, including tomato (<i>Solanum lycopersicum</i>), exhibit varying degrees of resistance. Dodder parasitism begins with the development of the haustorium, whose endophytic primordium undergoes intrusive growth to penetrate host tissues. While the cell walls of endophytic cells are essential for invasion, the sequential changes occurring in these cell walls are not fully understood. This study aims to characterize cell wall modifications in <i>Cuscuta campestris</i> haustoria during parasitism of a susceptible host (<i>Vigna radiata</i>) and a resistant host (<i>Solanum lycopersicum</i> 'Minibel'), using histochemical and immunohistochemical approaches focused on homogalacturonan (HG) and arabinogalactan proteins (AGPs). In both hosts, AGPs and HG (predominantly in their demethylesterified form) increased in the host-facing epidermal walls, the aligned file cells of the haustoria, and the boundary layer surrounding the haustorial cone. The boundary layer was enriched in AGPs and initially showed massive HG deposition, later incorporating lignin and callose. In tomato, lignin-based resistance was associated with the outermost cortical cells and did not substantially affect the overall dynamics of the dodder cell walls. These findings highlight the central role of coordinated cell wall remodeling in dodder invasion and reveal broadly similar developmental trajectories of HG and AGPs in haustoria formed on susceptible and resistant hosts.