Burkholderia phytofirmans PsJN primes Vitis vinifera L. and confers a better tolerance to low nonfreezing temperatures.

Several endophytic bacteria reportedly induce resistance to biotic stress and abiotic stress tolerance in several plant species. Burkholderia phytofirmans PsJN is a plant-growth-promoting rhizobacterium (PGPR) that is able to colonize grapevine tissues and induce resistance to gray mold. Further, PsJN induces physiological changes that increase grapevine tolerance to low nonfreezing temperatures. To better understand how bacteria induced the observed phenomena, stress-related gene expression and metabolite accumulation were monitored in 6-week-old Chardonnay grapevine plantlets after exposure to low nonfreezing temperatures. Under normal conditions (26°C), plantlet bacterization had no significant effect on the monitored parameters. By contrast, at 4°C, both stress-related gene transcripts and metabolite levels increased earlier and faster, and reached higher levels in PsJN-bacterized plantlets than in nonbacterized counterparts, in accordance with priming phenomena. The recorded changes may be correlated with the tolerance to cold stress conferred by the presence of PsJN. This is the first time that PGPR-induced priming has been shown to protect plants against low-temperature stress. Moreover, 1 week after cold exposure, levels of stress-related metabolites had declined more in PsJN-bacterized plants, suggesting that the endophyte is involved in the cold acclimation process via the scavenging system.

Characterization of a F-box gene up-regulated by phytohormones and upon biotic and abiotic stresses in grapevine.

F-box proteins are key components of the ubiquitin (Ub)/26S proteasome pathway that mediates selective degradation of regulatory proteins involved in a wide variety of cellular processes affecting eukaryotic cells. In plants, F-box genes form one of the largest multigene superfamilies and control many important biological functions. Among the F-box genes characterized to date only few have been involved in the regulation of plant defense responses. Moreover, no F-box genes have been studied and characterized in grapevine. Using a differential display approach we isolated a F-box gene (BIG-24.1), which is up-regulated during Botrytis cinerea infection of grapevine leaves. BIG-24.1 encodes a polypeptide of 386 amino acids with a conserved F-box domain in the N-terminus region and a kelch domain. By investigating expression profiles of BIG-24.1, we show that the gene expression is strongly stimulated in B. cinerea infected berries and in grapevine cells challenged by MAMP rhamnolipids, a non-host bacterium and an endophytic rhizobacterium. The gene is also strongly induced by abiotic stresses including UV-C and wounding or by salicylic acid, methyl-jasmonate, ethylene and abscisic acid that are known to be involved in defense signalling pathways. In addition, sequence analysis of the BIG-24.1 promoter revealed the presence of several regulatory elements involved in the activation of plant defense responses.

Comparative analysis of defence responses induced by the endophytic plant growth-promoting rhizobacterium Burkholderia phytofirmans strain PsJN and the non-host bacterium Pseudomonas syringae pv. pisi in grapevine cell suspensions.

Plant growth-promoting rhizobacteria (PGPR) are beneficial microorganisms that colonize the rhizosphere of many plant species and confer beneficial effects, such as an increase in plant growth. PGPR are also well known as inducers of systemic resistance to pathogens in plants. However, the molecular mechanisms involved locally after direct perception of these bacteria by plant cells still remain largely unknown. Burkholderia phytofirmans strain PsJN is an endophytic PGPR that colonizes grapevine and protects the plant against the grey mould disease caused by Botrytis cinerea. This report focuses on local defence events induced by B. phytofirmans PsJN after perception by the grapevine cells. It is demonstrated that, after addition to cell suspension cultures, the bacteria were tightly attaching to plant cells in a way similar to the grapevine non-host bacteria Pseudomonas syringae pv. pisi. B. phytofirmans PsJN perception led to a transient and monophasic extracellular alkalinization but no accumulation of reactive oxygen species or cell death were detected. By contrast, challenge with P. syringae pv. pisi induced a sustained and biphasic extracellular alkalinization, a two phases oxidative burst, and a HR-like response. Perception of the PGPR also led to the production of salicylic acid (SA) and the expression of a battery of defence genes that was, however, weaker in intensity compared with defence gene expression triggered by the non-host bacteria. Some defence genes up-regulated after B. phytofirmans PsJN challenge are specifically induced by exogenous treatment with SA or jasmonic acid, suggesting that both signalling pathways are activated by the PGPR in grapevine.