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Authors: Xianmin Meng, Feng Zhang, Wencai Yang and Qingmao Shang.
Horticultural Plant Journal (2024)
Abstract: "Grafting is an effective technique for increasing the resistance of vegetables to biotic and abiotic stresses. It has been widely applied to produce solanaceous and melon vegetables. Temperature is an important external factor affecting graft formation. However, the molecular mechanism by which external ambient temperature affects tomato graft formation remains unclear. In this study, we demonstrated that elevating ambient temperature during grafting to 35 °C for more than 24 h after grafting accelerated vascular reconnection. We generated self- or heterografted combinations between phyB1B2 and pif4 loss-of-function mutant and wild-type plants, and were mutants unresponsive to graft formation at elevated ambient temperature. In addition, elevated ambient temperature induced SlPIF4 expression during grafting. SlPIF4 directly binds the promoters of auxin biosynthesis genes SlYUCCAs and activates their expression. Further investigation revealed auxin accumulation in the graft junction under elevated ambient temperature. The results illuminate the mechanism by which the PHYB-PIF4-auxin module promotes tomato graft formation in response to elevated ambient temperature."
Authors: Liu Cong, Hutian Ling, Shanshan Liu, Azheng Wang, Rui Zhai, Chengquan Yang, Zhigang Wang and Lingfei Xu.
Journal of Plant Physiology (2023)
Abstract: "Flower bud formation is an important plant growth process. It has been reported that dwarfing rootstocks can significantly affect the flower bud formation of scions. In this study, we found the dwarfing rootstock ‘Yunnan’ quince could significantly increase the flowering rate of ‘Abbé Fetel’ pear scions. The RNA-sequencing data revealed significant changes in the expression of genes related to hormone pathways. Furthermore, hormone analyses indicated that ‘Yunnan’ quince significantly decreased the GA3 content and increased the cytokinin/auxin ratio in ‘Abbé Fetel’ pear apical buds. The hormone contents were consistent with the RNA-sequencing data. Moreover, we found the flower development-related genes PbAGL9 and PbCAL-A1 were significantly upregulated and PbTFL1 was significantly downregulated in ‘Abbé Fetel’/‘Yunnan’ quince apical buds. To further clarify the relationship between hormones and flowering-related genes, a hormone response assay was carried out. We found the expression levels of PbCAl-A1, PbTFL1 and PbAGL9 were regulated by hormones including GA3, CPPU and NAA. Y1H and dual-luciferase assays indicated that PbAGL9 significantly decreased the promoter activity of PbTFL1. In summary, ‘Yunnan’ quince upregulated PbCAL-A1 and PbAGL9, and downregulated PbTFL1 expression by decreasing the GA3 content and increasing the cytokinin/auxin ratio in ‘Abbé Fetel’ pear apical buds. Additionally, ‘Yunnan’ quince down-regulate PbTFL1 by upregulating the expression of PbAGL9, and eventually promoted floral induction in ‘Abbé Fetel’ pear."
Authors: Ai Zhang, Keita Matsuoka, Abdul Kareem, Madalen Robert, Pawel Roszak, Bernhard Blob, Anchal Bisht, Lieven De Veylder, Cătălin Voiniciuc, Masashi Asahina and Charles W. Melnyk.
Current Biology (2022)
Editor's view: Plants require an efficient regeneration system to heal wounds. Zhang et al. identify four DOF transcription factors that are rapidly activated at sites of wounding, graft formation, or tissue cutting. These DOFs are activated by cell-wall damage and auxin to promote tissue regeneration and wound healing.
Highlights: • Four DOF transcription factors are rapidly activated at wounding and grafting sites • Damage to or modifications of the cellulose and pectin matrix activate DOFs • DOFs regulate callus formation, tissue adhesion, and vascular regeneration at wounds • Wound-associated ERF115 and ANAC096 are also activated upon cell-wall damage
Abstract: "Wound healing is a fundamental property of plants and animals that requires recognition of cellular damage to initiate regeneration. In plants, wounding activates a defense response via the production of jasmonic acid and a regeneration response via the hormone auxin and several ethylene response factor (ERF) and NAC domain-containing protein (ANAC) transcription factors. To better understand how plants recognize damage and initiate healing, we searched for factors upregulated during the horticulturally relevant process of plant grafting and found four related DNA binding with one finger (DOF) transcription factors, HIGH CAMBIAL ACTIVITY2 (HCA2), TARGET OF MONOPTEROS6 (TMO6), DOF2.1, and DOF6, whose expression rapidly activated at the Arabidopsis graft junction. Grafting or wounding a quadruple hca2, tmo6, dof2.1, dof6 mutant inhibited vascular and cell-wall-related gene expression. Furthermore, the quadruple dof mutant reduced callus formation, tissue attachment, vascular regeneration, and pectin methylesterification in response to wounding. We also found that activation of DOF gene expression after wounding required auxin, but hormone treatment alone was insufficient for their induction. However, modifying cell walls by enzymatic digestion of cellulose or pectin greatly enhanced TMO6 and HCA2 expression, whereas genetic modifications to the pectin or cellulose matrix using the PECTIN METHYLESTERASE INHIBITOR5 overexpression line or korrigan1 mutant altered TMO6 and HCA2 expression. Changes to the cellulose or pectin matrix were also sufficient to activate the wound-associated ERF115 and ANAC096 transcription factors, suggesting that cell-wall damage represents a common mechanism for wound perception and the promotion of tissue regeneration."
Authors: Gregory Reeves, Anoop Tripathi, Pallavi Singh, Maximillian R. W. Jones, Amrit K. Nanda, Constance Musseau, Melanie Craze, Sarah Bowden, Joseph F. Walker, Alison R. Bentley, Charles W. Melnyk and Julian M. Hibberd.
Nature (2022)
Editor's view: Intra- and inter-specific grafting is possible in most orders of monocotyledonous plants, and this process could be used to combat diseases that affect crops, such as Panama disease in bananas.
Abstract: "Grafting is possible in both animals and plants. Although in animals the process requires surgery and is often associated with rejection of non-self, in plants grafting is widespread, and has been used since antiquity for crop improvement1. However, in the monocotyledons, which represent the second largest group of terrestrial plants and include many staple crops, the absence of vascular cambium is thought to preclude grafting2. Here we show that the embryonic hypocotyl allows intra- and inter-specific grafting in all three monocotyledon groups: the commelinids, lilioids and alismatids. We show functional graft unions through histology, application of exogenous fluorescent dyes, complementation assays for movement of endogenous hormones, and growth of plants to maturity. Expression profiling identifies genes that unify the molecular response associated with grafting in monocotyledons and dicotyledons, but also gene families that have not previously been associated with tissue union. Fusion of susceptible wheat scions to oat rootstocks confers resistance to the soil-borne pathogen Gaeumannomyces graminis. Collectively, these data overturn the consensus that monocotyledons cannot form graft unions, and identify the hypocotyl (mesocotyl in grasses) as a meristematic tissue that allows this process. We conclude that graft compatibility is a shared ability among seed-bearing plants."
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Authors: Grégoire Loupit, Lysiane Brocard, Nathalie Ollat, Sarah Jane Cookson. Journal of Experimental Botany (2023)
Abstract: "Grafting is a traditional horticultural technique that makes use of plant wound healing mechanisms to join two different genotypes together to form one plant. In many agricultural systems, grafting with rootstocks controls the vigour of the scion and/or provides tolerance to deleterious soil conditions such as the presence of soil pests or pathogens or limited or excessive water or mineral nutrient supply. Much of our knowledge about the limits to grafting different genotypes together comes from empirical knowledge of horticulturalists. Until recently, researchers believed that grafting monocotyledonous plants was impossible, because they lack a vascular cambium, and that graft compatibility between different scion/rootstock combinations was restricted to closely related genotypes. Recent studies have overturned these ideas and open up the possibility of new research directions and applications for grafting in agriculture. The objective of this review is to describe and assess these recent advances in the field of grafting and, in particular, the molecular mechanisms underlining graft union formation and graft compatibility between different genotypes. The challenges of characterizing the different stages of graft union formation and phenotyping graft compatibility are examined."
Authors: Yun Liu, Hetong Liu, Tianyue Zhang, Junyi Liu, Xianzhi Sun, Xia Sun, Wenli Wang and Chengshu Zheng.
Scientia Horticulturae (2023)
Highlights • Rootstock affected gene expressions in the scion. • mRNAs in rootstock and scion played an important role in information transfer. • The miRNAs involved in the regulation of grafting were briefly described. • DNA methylation in grafting.
Abstract: "Grafting is an important method to improve plant yield and quality. The rootstock is vital to the scion in terms of growth and development, flowering and fruit set, and improved stress resistance. In the course of grafting, the rootstock and scion interactions and their molecular regulation mechanisms are extremely complex. This paper mainly discussed the following 7 changes happened to the plant during grafting: morphological characteristics of rootstock and scion healing, compound exchange between rootstock and scion interactions, phytohormone regulatory effects, gene expression, long-distance transport of mRNAs, mediating effects of sRNAs, and DNA methylation. It was aimed to provide a reference basis for efficient use of grafting technology to improve crop yield and quality, and to shorten crop breeding cycles."
Authors: Phanu T. Serivichyaswat, Kai Bartusch, Martina Leso, Constance Musseau, Akira Iwase, Yu Chen, Keiko Sugimoto, Marcel Quint and Charles W. Melnyk.
Development (2022)
One-sentence summary: This paper describes a pathway in which high temperatures are perceived by the leaves to promote an auxin-dependent signal that accelerates vascular regeneration, graft formation and plant parasitism in distant tissues.
Abstract: "Cellular regeneration in response to wounding is fundamental to maintain tissue integrity. Various internal factors including hormones and transcription factors mediate healing, but little is known about the role of external factors. To understand how the environment affects regeneration, we investigated the effects of temperature upon the horticulturally relevant process of plant grafting. We found that elevated temperatures accelerated vascular regeneration in Arabidopsis thaliana and tomato grafts. Leaves were crucial for this effect, as blocking auxin transport or mutating PHYTOCHROME INTERACTING FACTOR 4 (PIF4) or YUCCA2/5/8/9 in the cotyledons abolished the temperature enhancement. However, these perturbations did not affect grafting at ambient temperatures, and temperature enhancement of callus formation and tissue adhesion did not require PIF4, suggesting leaf-derived auxin specifically enhanced vascular regeneration in response to elevated temperatures. We also found that elevated temperatures accelerated the formation of inter-plant vascular connections between the parasitic plant Phtheirospermum japonicum and host Arabidopsis, and this effect required shoot-derived auxin from the parasite. Taken together, our results identify a pathway whereby local temperature perception mediates long distance auxin signaling to modify regeneration, grafting and parasitism."
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