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A nice step towards achieving wide spread inter-species plant grafting "Cell-cell adhesion in plant grafting is facilitated by β-1,4-glucanases" published today in @ScienceMagazine. My thoughts on this paper 
https://science.sciencemag.org/content/369/6504/698
https://science.sciencemag.org/content/369/6504/698
Notaguchi and colleagues discovered that you can *successfully* graft Nicotiana to most plants tested (73/84 species successful from 38 plant families) including monocots, eudicots and magnoliids
What is so special about Nicotiana? You can’t graft any plant to 73 different species. Transcriptome analyses of the inter-species graft revealed upregulation of many genes including a glycosyl hydrolase 9B (NbGH9B3) that they hypothesize is important for cell-to-cell adhesion
Knocking down or overexpressing this gene (NbGH9B3) modified the ability of plants to graft, suggesting indeed it plays an important role
However, this glycosyl hydrolase 9B3 is upregulated in many plants during grafting, including some unsuccessful combinations. It could be that the Nicotiana gene is special, upregulation is stronger in compatible grafts, or some other mechanism determines compatibility.
The key experiment needed is putting this gene into an incompatible combination to allow grafting to succeed.
Another side note: many of these grafted plants look sick. The vascular connectivity data in the paper is not strong and I suspect these inter-species combinations have poor vascular connections. However, a first step in a very interesting direction.
I wrote *successfully* because there are different ways to measure graft success: both short-term and long-term compatibility. Sick looking graft combinations would argue these are incompatible grafts that are tolerated but don’t allow the plant to grow normally. An example:
A cool side note: these β-1,4-glucanase genes are also important for plant parasitism ( https://www.nature.com/articles/s42003-020-01143-5) and might play a conserved role for inter-species tissue adhesion. Grafting and parasitism come together! /end
