Graft-union development: a delicate process that involves cell–cell communication between scion and stock for local auxin accumulation

Abstract

Grafting is an ancient cloning method that has been used widely for thousands of years in agricultural practices. Graft-union development is also an intricate process that involves substantial changes such as organ regeneration and genetic material exchange. However, the molecular mechanisms for graft-union development are still largely unknown. Here, a micrografting method that has been used widely in Arabidopsis was improved to adapt it a smooth procedure to facilitate sample analysis and to allow it to easily be applied to various dicotyledonous plants. The developmental stage of the graft union was characterized based on this method. Histological analysis suggested that the transport activities of vasculature were recovered at 3 days after grafting (dag) and that auxin modulated the vascular reconnection at 2 dag. Microarray data revealed a signal-exchange process between cells of the scion and stock at 1 dag, which re-established the communication network in the graft union. This process was concomitant with the clearing of cell debris, and both processes were initiated by a wound-induced programme. The results demonstrate the feasibility and potential power of investigating various plant developmental processes by this method, and represent a primary and significant step in interpretation of the molecular mechanisms underlying graft-union development.

Graft incompatibility in plants: Metabolic changes during formation and establishment of the rootstock/scion union with emphasis on Prunus species

“…It is now known that some mRNA signals change just 24 h after grafting, and that 48 h after grafting auxins increase at the union and stimulate cell division and differentiation. On the third day, transport was already functioning across the graft union (Yin et al, 2012;Koepke and Dhingra, 2013). This is an indication that new xylem and phloem formation follow the same pattern described by Dengler (2001) in normal shoots and roots.…”

“…In grafted plants, vascular regeneration is a complex process that includes structural differentiation of the parenchymatous tissue from both sides of the graft union into xylem and phloem (Olmstead et al, 2006;Aloni et al, 2010). The sequence of structural events occurring during the healing of the graft union in woody and herbaceous plants has been reviewed by several authors (Moing and Carde, 1988;Tiedemann, 1989;Hartmann et al, 2002;Pina and Errea, 2005), but recently Yin et al (2012) identified six major events: (i) Wound-induced response, (ii) cleanup of cell debris, (iii) cellular communication, (iv) auxin accumulation and responses, (v) cell division and differentiation, and (vi) vascular reconnection. It is now known that some mRNA signals change just 24 h after grafting, and that 48 h after grafting auxins increase at the union and stimulate cell division and differentiation.…”

Selection of resistant rootstocks to Meloidogyne enterolobii and M. incognita for okra (Abelmoschus esculentus L. Moench)

“…In Arabidopsis sp., Yin et al (2012) found that the functional establishment of the conducting vessels is detectable on the third day after grafting. However, Turnbull (2010), in similar work, claimed that the total lignification of conducting vessels could only occur 7 to 12 d after grafting.…”

“…Such changes disrupt the normal flow of endogenous auxin and may be responsible for this distortion (Cano-Delgado et al, 2010). This hypothesis has received empirical support by Yin et al (2012), who demonstrated the involvement of auxin in the initial stages of the formation of the graft union.…”

Signaling pathway in development of Camellia oleifera nurse seedling grafting union

“…Grafting generates an impulse to elicit healing mechanism that generates biological response (isolation layer formation, callus differentiation, callus proliferation and connection, cambium differentiation and connection, and conducting tissue differentiation and connection) (Estrada-Luna et al 2002;Fan et al 2015). Studies conducted on graft-healing mechanism focused on determining the quantities of various biochemical substances in the scion (Pina and Errea 2005;Aloni et al 2008;Muneer et al 2016), enzyme activity (Zarrouk et al 2010), and endogenous hormone content (Aloni et al 2008;van Hooijdonk et al 2011;Yin et al 2012), all of which vary with the healing stage; however, signaling pathways of grafting healing was seldom reached.…”