Host-parasite tissue adhesion by a secreted type of β-1,4-glucanase in the parasitic plant Phtheirospermum japonicum
Tissue adhesion between plant species occurs both naturally and artificially. Parasitic plants establish symbiotic relationship with host plants by adhering tissues at roots or stems. Plant grafting, on the other hand, is a widely used technique in agriculture to adhere tissues of two stems. While compatibility of tissue adhesion in plant grafting is often limited within close relatives, parasitic plants exhibit much wider compatibilities. For example, the Orobanchaceae parasitic plant Striga hermonthica is able to infect Poaceae crop plants, causing a serious agricultural loss. Here we found that the model Orobanchaceae parasite plant Phtheirospermum japonicum can be grafted on to interfamily species, such as Arabidopsis, a Brassicaceae plant. To understand molecular basis of tissue adhesion between distant plant species, we conducted comparative transcriptome analyses on both infection and grafting by P. japonicum on Arabidopsis. Through gene clustering, we identified genes upregulated during these tissue adhesion processes, which include cell proliferation- and cell wall modification-related genes. By comparing with a transcriptome dataset of interfamily grafting between Nicotiana and Arabidopsis, we identified 9 genes commonly induced in tissue adhesion between distant species. Among them, we showed a gene encoding secreted type of {beta}-1,4-glucanase plays an important role for plant parasitism. Our data provide insights into the molecular commonality between parasitism and grafting in plants. Significance StatementComprehensive sequential RNA-Seq datasets for parasitic infection of the root and grafting of the stem between P. japonicum and Arabidopsis revealed that molecular events of parasitism and grafting are substantially different and only share a part of events such as cell proliferation and cell wall modification. This study demonstrated that a secreted type of {beta}-1,4-glucanase gene expressed in cells located at the parasite-host interface as an important factor for parasitism in the Orobanchaceae.