Plant grafting: insights into tissue regeneration

Abstract

For millennia, people have cut and joined different plants together through a process known as grafting. The severed tissues adhere, the cells divide and the vasculature differentiates through a remarkable process of regeneration between two genetically distinct organisms as they become one. Grafting is becoming increasingly important in horticulture where it provides an efficient means for asexual propagation. Grafting also combines desirable roots and shoots to generate chimeras that are more vigorous, more pathogen resistant and more abiotic stress resistant. Thus, it presents an elegant and efficient way to improve plant productivity in vegetables and trees using traditional techniques. Despite this horticultural importance, we are only beginning to understand how plants regenerate tissues at the graft junction. By understanding grafting better, we can shed light on fundamental regeneration pathways and the basis for self/non‐self recognition. We can also better understand why many plants efficiently graft whereas others cannot, with the goal of improving grafting so as to broaden the range of grafted plants to create even more desirable chimeras. Here, I review the latest findings describing how plants graft and provide insight into future directions in this emerging field.

Transcriptome dynamics at theArabidopsisgraft junction reveal an inter-tissue recognition mechanism that activates vascular regeneration

“…Thus, proteins such as ALF4 or AXR1 577 might enhance or promote a rootstock-specific auxin response and could be 578 particularly important when there is incomplete attachment, cellular damage or 579 inefficient transport. All higher plants transport auxin from shoot to root, yet not 580 all plant species can be successfully grafted (Melnyk, 2017c) so the response to 581 auxin rather than the transport itself may be a determining factor in the ability to 582 graft. A role for sugars is not completely ruled out though, since the magnitude of 583 differential expression was often lower in the grafted bottom and exogenous 584 sugar reduced grafting efficiency (Figure 2A).…”

Cell–cell adhesion in plant grafting is facilitated by β-1,4-glucanases

“…Plant grafting is the procedure of connecting two or more pieces of living plant tissues to grow as a single plant, for which the healing of the wound site is accomplished through the adhesion of proliferated cells 2–4 . Use of grafting is necessary for propagation of many fruit trees worldwide, such as apples, pears, grapes, and citrus, for vegetable cultivation in Asian and European countries to obtain the benefits of certain rootstocks, such as disease resistance and tolerance of unfavorable soil conditions, and to control the quantity and quality of fruit 1,8 .…”

“…Although grafting is a useful technique, for practical use the scion–stock combination (the shoot and root parts of a graft, respectively) is limited to closely related plant species. In general, grafting is successful between members of the same species, genus, and family, but not between members of different families because of graft incompatibility 2–4,9 . However, several interfamily graft combinations have been reported 12–17 , including a combination we have studied previously involving a Nicotiana benthamiana scion ( Nb , Solanaceae) and an Arabidopsis thaliana stock ( At , Brassicaceae) 18 , in which the Nb scion grew slowly but distinctly (Supplementary Movie 1, Extended data Fig.…”

“…Plant grafting has mostly relied on the natural ability of a plant for wound healing. However, the compatibility of cell–cell adhesion typically limits graft combinations to closely related species 2–4 , and the mechanism by which cell–cell adhesion of injured tissues is established is largely unknown. Here, we show that a subclade of β-1,4-glucanases secreted into the extracellular region facilitates cell–cell adhesion near the graft interface.…”

Control of Cucumber green mottle mosaic virus in commercial greenhouse production with agricultural disinfectants and resistant cucumber varieties

“…While breeding for viral disease resistance is a long-term process, vegetable grafting offers a short term alternative for compiling tolerance traits and improving yield potential (Pérez-Alfocea, 2015;Rouphael et al, 2018). Grafted plants have greater tolerance to biotic and abiotic stresses thus providing higher fruit yields (Louws et al, 2010;Melnyk, 2016). The enhanced tolerance in grafted plants has been attributed to increases in vigor, improved photosynthetic efficiency, stronger antioxidative defense system, heightened hormonal signaling and long-distance movement of mRNAs, small RNAs and proteins (Davis et al, 2008;Rouphael et al, 2018).…”