No abstract

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.

Biosurfactants are amphiphilic surface-active molecules that are produced by a variety of microorganisms including fungi and bacteria. Pseudomonas, Burkholderia, and Bacillus species are known to secrete rhamnolipids and lipopeptides that are used in a wide range of industrial applications. Recently, these compounds have been studied in a context of plant-microbe interactions. This mini-review describes the direct antimicrobial activities of these compounds against plant pathogens. We also provide the current knowledge on how rhamnolipids and lipopeptides stimulate the plant immune system leading to plant resistance to phytopathogens. Given their low toxicity, high biodegradability and ecological acceptance, we discuss the possible role of these biosurfactants as alternative strategies to reduce or even replace pesticide use in agriculture.

Albinism remains a major problem in cereal improvement programs that rely on doubled haploid (DH) technology, and the factors controlling the phenomenon are not well understood. Here we report on the positive influence of copper on the production of DH plants obtained through microspore embryogenesis (ME) in recalcitrant cultivars of barley (Hordeum vulgare L.). The presence of copper sulphate in the anther pre-treatment medium improved green DH plant regeneration from cultivars known to produce exclusively albino plants using classical procedures. In plastids, the effect of copper was characterized by a decrease in starch and a parallel increase in internal membranes. The addition of copper sulphate in the ME pre-treatment medium should enable breeders to exploit the genetic diversity of recalcitrant cultivars through DH technology. We examined programmed cell death (PCD) during microspore development to determine whether PCD may interfere with the induction of ME and/or the occurrence of albinism. By examining the fate of nuclei in various anther cell layers, we demonstrated that the kinetics of PCD in anthers differed between the barley cultivars Igri and Cork that show a low and a high rate of albinism, respectively. However, no direct correlation between PCD in the anther cell layers and the rate of albinism was observed and copper had no influence on the PCD kinetic in these cultivars. It was concluded that albinism following ME was not due to PCD in anthers, but rather to another unknown phenomenon that appears to specifically affect plastids during microspore/pollen development.