Impossible Achieved! Cambridge University Realizes Grafting In Monocotyledonous Plants, Overturning Previous Cognitions

"Impossible" Achieved! Cambridge University Realizes Grafting in Monocotyledonous Plants, Overturning Previous Cognitions. Plant grafting is widespread and has been used for crop improvement since ancient times. However, in monocotyledonous plants, due to the absence of a vascular cambium, it was previously believed that grafting could not be performed. The journal Nature published online a research paper titled "Monocotyledonous plants graft at the embryonic root–shoot interface" by Julian M. Hibberd's research group from the University of Cambridge. This research successfully achieved grafting technology in monocotyledonous plants, overturning the previous cognition that monocotyledonous plants cannot be grafted. Therefore, this study shows that grafting compatibility is a common ability among seed plants. Grafting is an ancient agricultural method that relies on the plant's ability to self-repair. Grafting connects independent root and shoot systems to form a two-plant system that exhibits superior traits. Successful grafting depends on the formation of the graft interface, a dynamic anatomical connector that combines the stock and scion. Previously, it was thought that grafting of monocotyledonous plants was an almost impossible task, and failures were attributed to anatomical differences between monocotyledonous and dicotyledonous plants, especially the absence of an inner cell layer unique to dicotyledonous plants in monocotyledonous plants, namely the vascular cambium.

This research first hypothesized that undifferentiated or embryonic callus can be grafted in monocotyledonous plants. Through multiple experiments, this study used germinating seeds in wheat. The plumule of one plant embryo was removed and replaced with the plumule of another donor seed, and it was ensured that the transplanted part was in close contact with the radicle and could develop into a graft-like plant. Further, a transgenic pUBIQUITIN::GUS wheat line was used to prove that genetically different plants can also be grafted and grow to maturity. With this method, the graft union forms in the hypocotyl, which separates the plumule and radicle.

When the plumule is excised and replaced in seeds of the same species, the efficiency of grafted wheat can be up to 79%. In addition, different hexaploid wheat genotypes are also successfully fused with an efficiency of 31%. After that, this study also achieved grafting in rice using a similar method, illustrating the feasibility of monocotyledonous plant grafting. See the figure below: Next, this study also tested whether grafting can be performed in other monocotyledonous taxa. Among 11 monocotyledonous orders, dozens of species spanning nine phylogenetically different orders can self-graft. In addition, grafting can also be completed between two very different cereals, such as grafting wheat and sorghum. After that, this study also tested whether stem traits can be modified by grafting in monocotyledonous plants.

When a wild-type rice stock is fused with a scion containing a mutation in the carotenoid cleavage dioxygenase 8 gene related to strigolactone hormone biosynthesis, this rescues the excessive tillering phenotype caused by strigolactone deficiency. In addition, when oat stocks are grafted onto wheat scions, wheat is tolerant to Fusarium graminearum, indicating that grafting monocotyledonous plants can bring agricultural benefits. Finally, this study revealed through RNA-seq methods that genes in cells near the graft junction are rapidly reprogrammed, and many of these genes are related to the regeneration process and are precursors to graft formation. Some of the gene expression patterns observed in this study are very similar to those seen during the formation of dicotyledonous plant grafts, and some gene expression patterns are unique to monocotyledonous plants. In conclusion, the research results of this study overturn the consensus that the vascular cambium is a prerequisite for plant graft formation, indicating that the embryonic hypocotyl allows most monocotyledonous plants to be grafted.