Cell Wall Dynamics in a Plant-Plant Pathosystem

In the plant-plant pathosystem of Oryza sativa and the parasitic plant Striga hermonthica, cell walls from either plant are important defensive and offensive structures. Here we reveal cell wall dynamics in both Striga and rice using simultaneous RNA sequencing. We used weighted gene co-expression network analysis (WGCNA) to home in on cell wall modification processes occurring in a resistant rice genotype (Nipponbare) compared to a susceptible one (IAC 165). Likewise, we compared the cell wall dynamics in Striga infecting resistant and susceptible rice. Our study revealed an intense battlement at the rice-Striga cell walls involving both host (defense) and parasite (offense) factors; the outcome of which makes the difference between successful or failed parasitism. Striga activates genes encoding cell wall degrading enzymes (CWDEs) to gain access to the host; expansins and pectin lyases to allow cell elongation and methyl estereses and lignin synthesis for rigidity during infection. In the susceptible host, immune response processes are not induced and Striga derived CWDEs easily breach the host cell wall resulting in successful parasitism. In contrast, the resistant host invokes immune responses modulated by phytohormones to fortify cell wall through polysaccharides and lignin deposition. Through these processes, the cell wall of the resistant host successfully obstructs parasite entry. We discuss the implications of these findings in the context of practical agriculture in which cell wall modification can be used to manage parasitic plants.