How Streptomyces anulatus Primes Grapevine Defenses to Cope with Gray Mold: A Study of the Early Responses of Cell Suspensions

Abstract

Gray mold, caused by Botrytis cinerea, is one of the most destructive diseases of grapevine and is controlled with an intense application of fungicides. As alternatives to chemicals, beneficial microbes may promote plant health by stimulating the plant’s immune system. An actinomycete, Streptomyces anulatus S37, has been screened from the rhizosphere microbiome of healthy Vitis vinifera on the basis of its ability to promote grapevine growth and to induce resistance against various phytopathogens, including B. cinerea. However, molecular mechanisms involved locally after direct perception of these bacteria by plant cells still remain unknown. This study focuses on local defense events induced in grapevine cells during interactions with S. anulatus S37 before and after pathogen challenge. We demonstrated that S. anulatus S37 induced early responses including oxidative burst, extracellular alkalinization, activation of protein kinases, induction of defense gene expression and phytoalexin accumulation, but not the programmed cell death. Interestingly, upon challenge with the B. cinerea, the S. anulatus S37 primed grapevine cells for enhanced defense reactions with a decline in cell death. In the presence of the EGTA, a calcium channel inhibitor, the induced oxidative burst, and the protein kinase activity were inhibited, but not the extracellular alkalinization, suggesting that Ca2+ may also contribute upstream to the induced defenses. Moreover, desensitization assays using extracellular pH showed that once increased by S. anulatus S37, cells became refractory to further stimulation by B. cinerea, suggesting that grapevine cells perceive distinctly beneficial and pathogenic microbes.

Exploring Two Streptomyces Species to Control Rhizoctonia solani in Tomato

“…The present study demonstrated the role of two Streptomyces strains in promotion of plant growth which are consistent with other studies [14,20,30,[75][76][77]. The present findings are consistent with other previous studies which showed that beneficial bacteria prime plant host for a quicker and a boosted capacity to trigger plant defense responses such as the activation of some defense related genes upon the pathogen challenge [62,70].…”

“…JA and ethylene are signaling molecules that play a basic role in induced systemic resistance (ISR) pathway [1,69]. Similar to our results, the treatment of grapevine plant with S. anulatus S37 triggered the defense-related genes expression, including genes encoding secondary metabolism of PAL and LOX in response to Botrytis cinerea challenge [70]. Nevertheless, despite the level of gene expression being low during the interaction between S. globisporous strain F8 or S. praecox strain R7 and pathogen in the tomato plant, it may suggest the involvement of JA and SA signaling pathways upon the strain's perception, as reflected by the increased expression of LOX, which is a key element of the oxylipin synthesis, and an induced expression of PAL gene, which was found to be induced by SA.…”

“…Various studies have advocated that most beneficial bacteria primed plants to trigger several cellular defense responses against the pathogen assault [70,73]. Martinez-Hidalgo et al [22] showed that in the expression of LOXA and PinΠ, the JA marker genes increased significantly upon Botrytis cinerea challenge in Micromonospora-treated tomato plants.…”

The Role of the Endophytic Microbiome in the Grapevine Response to Environmental Triggers

“…Streptomyces anulatus S37 isolated from wild V. vinifera is an endophytic PGP rhizobacterium (PGPR) that confers resistance against different pathogens, including B. cinerea (Loqman et al, 2009). Vatsa-Portugal et al (2017) showed that S. anulatus S37 perception by grapevine cells triggers early and late defense responses, such as ion fluxes, oxidative burst, extracellular alkalinization, activation of protein kinases, induction of defense gene expression, and phytoalexin accumulation. Moreover, S. anulatus S37-primed grapevine cells became refractory to infection by B. cinerea , showing a reduction in pathogen-induced cell death (Vatsa-Portugal et al, 2017).…”

Potential of Bioremediation and PGP Traits in Streptomyces as Strategies for Bio-Reclamation of Salt-Affected Soils for Agriculture

“…In some cases, bacteria can act in a vaccine-like fashion, eliciting non-specific plant defense mechanisms. This effect provides the host with resistance against pathogens via different mechanisms along the plant infection cycle [122][123][124]. Additionally, the use of some strains in the production of insecticides renders and environmentally friendly approach to control pests and disease without the application of synthetic compounds [99,102].…”