Graft union formation in grapevine induces transcriptional changes related to cell wall modification, wounding, hormone signalling, and secondary metabolism

Abstract

Grafting is particularly important to the cultivation of perennial crops such as grapevine (Vitis vinifera) because rootstocks can provide resistance to soil-borne pests and diseases as well as improve tolerance to some abiotic stresses. Successful grafting is a complex biochemical and structural process beginning with the adhesion of the two grafted partners, followed by callus formation and the establishment of a functional vascular system. At the molecular level, the sequence of events underlying graft union formation remains largely uncharacterized. The present study investigates the transcriptome of grapevine rootstock and graft interface tissues sampled 3 d and 28 d after grafting of over-wintering stems in the spring. Many genes were differentially expressed over time, from 3 d to 28 d after grafting, which could be related to the activation of stem growth and metabolic activity in the spring. This hypothesis is supported by the up-regulation of many genes associated with cell wall synthesis, and phloem and xylem development. Generally, there was an up-regulation of gene expression in the graft interface tissue compared with the rootstock, particularly genes involved in cell wall synthesis, secondary metabolism, and signalling. Although there was overlap between the genes differentially expressed over time (from 3 d to 28 d after grafting) with the gene differentially expressed between the rootstock and the graft interface, numerous graft interface-specific genes were identified.

Heterografting with nonself rootstocks induces genes involved in stress responses at the graft interface when compared with autografted controls

“…The scion CS was grafted onto RG (CS/RG) and 1103P (CS/1103P) as well as autografted onto CS rootstocks (CS/CS) (as described by Cookson et al , 2013). …”

“…Many genes were differentially expressed over time, from 3 to 28 d after grafting, but they will not be discussed here as they have been described previously (Cookson et al , 2013). The scion/rootstock graft interfaces studied were: the autograft Vitis vinifera cv.…”

Developments at the graft interface in homo- and hetero-grafts

“…7 When transcriptome of grapevine rootstock and graft interface tissues sampled 3 and 28 dag were studied in homo-grafts (CS grafted with itself), we observed that homo-graft union development in grapevine involved the upregulation of many genes involved in cell wall synthesis, wound responses, secondary metabolism and signaling. 4 These gene expression differences were accompanied by the accumulation of callose, lignin and cellulose in the callus cells at the graft interface (Fig. 1.…”

“…Up until very recently, the only gene expression studies published on grafting concerned homo-grafting where processes presumably similar to simple wound-like responses 6,7,4 seem to occur.…”

Effects of rootstock genotypes on compatibility, biomass, and the yield of Welschriesling

“…The mechanism of graft incompatibility of grapevine is not fully understood. Researchers studied how the union develops and functions over time (Pina, Errea 2005;Darikova et al 2011;Cookson et al 2013), and confirmed that incompatibility between different scion-rootstock combinations my occur (Gökbayrak et al 2007). This incompatibility can be detected few weeks after grafting and linked to a poor vascular connection and phloem degeneration at the graft union.…”