Plant grafting is conducted for fruit and vegetable propagation, whereby a piece of living tissue is attached to another through cell-cell adhesion. However, graft compatibility limits combinations to closely related species, and the mechanism is poorly understood. We found that Nicotiana is capable of graft adhesion with a diverse range of angiosperms. Comparative transcriptomic analyses on graft combinations indicated that a subclade of β-1,4-glucanases secreted into the extracellular region facilitates cell wall reconstruction near the graft interface. Grafting was promoted by overexpression of the β-1,4-glucanase. Using Nicotiana stem as an interscion, we produced tomato fruits on rootstocks from other plant families. These findings demonstrate that the process of cell-cell adhesion is a potential target to enhance plant grafting techniques.

Bacteria and fungi form complex communities (microbiomes) in above- and below-ground organs of plants, contributing to hosts’ growth and survival in various ways. Recent studies have suggested that host plant genotypes control, at least partly, plant-associated microbiome compositions. However, we still have limited knowledge of how microbiome structures are determined in/on grafted crop plants, whose above-ground (scion) and below-ground (rootstock) genotypes are different with each other. By using eight varieties of grafted tomato plants, we examined how rootstock genotypes could determine the assembly of leaf endophytic microbes in field conditions. An Illumina sequencing analysis showed that both bacterial and fungal community structures did not significantly differ among tomato plants with different rootstock genotypes: rather, sampling positions in the farmland contributed to microbiome variation in a major way. Nonetheless, a further analysis targeting respective microbial taxa suggested that some bacteria and fungi could be preferentially associated with particular rootstock treatments. Specifically, a bacterium in the genus Deinococcus was found disproportionately from ungrafted tomato individuals. In addition, yeasts in the genus Hannaella occurred frequently on the tomato individuals whose rootstock genotype was “Ganbarune”. Overall, this study suggests to what extent leaf microbiome structures can be affected/unaffected by rootstock genotypes in grafted crop plants.

Tissue adhesion between plant species occurs both naturally and artificially. Parasitic plants establish intimate 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. Here we found that the model Orobanchaceae parasitic plant Phtheirospermum japonicum can be grafted on to interfamily species. 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 . Despite different organs, we identified the shared gene expression profile, where cell proliferation- and cell wall modification-related genes are up-regulated. Among genes commonly induced in tissue adhesion between distant species, we showed a gene encoding a secreted type of β-1,4-glucanase plays an important role for plant parasitism. Our data provide insights into the molecular commonality between parasitism and grafting in plants.

Plant grafting is conducted for vegetative propagation in plants, whereby a piece of 1 living tissue is attached to another tissue through establishment of cell-cell adhesion. 2Plant grafting has a long history in agriculture and has been applied to improve 3 crop traits for thousands of years 1 . Plant grafting has mostly relied on the natural 4 ability of a plant for wound healing. However, the compatibility of cell-cell adhesion 5 typically limits graft combinations to closely related species 2-4 , and the mechanism 6 by which cell-cell adhesion of injured tissues is established is largely unknown. Here, 7we show that a subclade of β-1,4-glucanases secreted into the extracellular region 8 facilitates cell-cell adhesion near the graft interface. Nicotiana shows a propensity 9 for cell-cell adhesion with a diverse range of angiosperms, including vegetables, 10 fruit trees, and monocots, in which cell wall reconstruction was promoted in a 11 similar manner to conventional intrafamily grafting 5-7 . Using transcriptomic 12 approaches, we identified a specific clade of β-1,4-glucanases that is upregulated 13 during grafting in successful graft combinations but not in incompatible grafts and 14 precedes graft adhesion in inter-and intrafamily grafts. Grafting was facilitated 15 with an overexpressor of the β-1,4-glucanase and, using Nicotiana stem as an 16 interscion, we produced tomato fruits on rootstocks from other plant families. Our 17 results demonstrate that the mechanism of cell-cell adhesion is partly conserved in 18 plants and is a potential target to enhance plant grafting techniques. 19

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 β-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 β-1,4-glucanase gene expressed in cells located at the parasite–host interface as an important factor for parasitism in the Orobanchaceae.