Transcriptional regulation of stilbene synthases in grapevine germplasm differentially susceptible to downy mildew

Abstract

Background To limit the impact of the downy mildew disease of grapevine and reduce the need to recur to chemical treatments, an effective strategy might be recovering adaptive resistance traits in both cultivated and wild V. vinifera germplasm. Considering that stilbenes represent the most important class of phytoalexins in the Vitaceae, the constitutive expression and transcriptional activation of all the functional members of the stilbene synthase gene family were analysed in a group of nine grapevine genotypes following artificial infection with the oomycete Plasmopara viticola, the causal agent of the disease. In addition, in the same genotypes we analyzed the expression of genes encoding for two transcription factors involved in the transcriptional regulation of the stilbene synthase genes, namely VvMYB14 and VvMYB15, and of genes encoding for chalcone synthases. Results Downy mildew incidence and severity ranged from nihil to high in the grapevine genotypes considered, being low to moderate in a subgroup of V. vinifera genotypes. The constitutive expression of the stilbene synthase genes as well as the extent of their transcriptional activation following P. viticola inoculation appeared to be inversely related to the proneness to develop disease symptoms upon infection. In a specular manner, following P. viticola inoculation all the chalcone synthase genes were up-regulated in the susceptible grapevine genotypes and down-regulated in the resistant ones. The infection brought by P. viticola appeared to elicit a co-ordinated and sequential transcriptional activation of distinct stilbene synthase genes subsets, each of which may be regulated by a distinct and specific MYB transcription factor. Conclusions The present results suggest that the induction of stilbene biosynthesis may contribute to the basal immunity against the downy mildew of grapevine, thus representing an adaptive resistance trait to recover, in both cultivated and wild V. vinifera germplasm. During the early stages of P. viticola infection, an antagonistic interaction between flavonol and stilbene biosynthesis might occur, whose outcome might determine the subsequent extent of disease symptoms. Further studies are needed to decipher the possible regulatory mechanisms involved in the antagonistic crosstalk between these two metabolic pathways in resistant and susceptible genotypes in response to P. viticola.

Biological and molecular interplay between two viruses and powdery and downy mildews in two grapevine cultivars

“…The first important factor inducing transcriptional modulation of the genes was the time (T0 and Tf) associated with inoculation of DM and PM causal agents. In some genes at Tf, the responses induced by P. viticola and E. necator were not always in line with the data reported for these pathogens 34 , 42 , 43 . This is because we chose to focus on the systemic responses induced by these biotrophic pathogens over a long period by sampling only asymptomatic leaves at Tf and we did not consider the early molecular responses in infected tissues, which were well characterized in DM 34 , 42 and PM 43 .…”

“…In some genes at Tf, the responses induced by P. viticola and E. necator were not always in line with the data reported for these pathogens 34 , 42 , 43 . This is because we chose to focus on the systemic responses induced by these biotrophic pathogens over a long period by sampling only asymptomatic leaves at Tf and we did not consider the early molecular responses in infected tissues, which were well characterized in DM 34 , 42 and PM 43 . An example of this discrepancy was the regulation of VvPR1 and VvBgluc , two genes codifying PR proteins, which are generally upregulated in the first days after the infection of P. viticola 42 , 44 and E. necator 43 , 45 .…”

“…Stilbene synthases are a class of genes of the phenylpropanoid metabolism and are strongly involved in plant responses to environmental stresses, and in grapevine VvSTS48 , VvSTS16 , and VvSTS19 (Fig. 1 ) are involved in the response to fungal pathogens 34 . All three genes were overexpressed at Tf and expression levels systemically induced by E. necator (Tf_EN) were much higher than those observed after P. viticola (Tf_PV) inoculation (Fig.…”

“…Stilbene synthases ( VvSTSs ) showed strong overexpression at Tf in all cases for both pathogens, and at Tf_EN these genes were expressed 3 to 10 times more than at Tf_PV. Stilbenes are the most important class of phytoalexins, which represent a powerful defence system against several pathogens, including P. viticola and E. necator 34 , 43 , 46 , and are key molecules of basal immunity in grapevine 47 , 48 . Defense responses involving VvSTSs persisted for a long period after inoculation with both pathogens, with higher levels after E. necator inoculation.…”

Long-Term Impact of Chemical and Alternative Fungicides Applied to Grapevine cv Nebbiolo on Berry Transcriptome

“…Despite that significantly differences in berry skin phenolic compositions have not been found among the several treatments [ 22 ], it is worth noting the downregulation of almost all the DEGs involved in response to stress and secondary metabolite categories, with a few exceptions in berries treated by Met. Stilbenes represent the most important class of phytoalexins in Vitis and accumulate in response to several environmental stress factors, including pathogen attack [ 43 ]. The biosynthetic pathway that leads to the stilbene production is a side branch of the general phenylpropanoid pathway and the key enzymes in the biosynthesis of these compounds are the stilbene synthases (STSs) that compete for the same substrates (p-coumaroyl-CoA and cinnamoyl-CoA) with chalcone synthases (CHSs), the key enzymes in the biosynthesis of flavonoids.…”