AUTHOR=Trotel-Aziz Patricia , Abou-Mansour Eliane , Courteaux Barbara , Rabenoelina Fanja , Clément Christophe , Fontaine Florence , Aziz Aziz 

TITLE=Bacillus subtilis PTA-271 Counteracts Botryosphaeria Dieback in Grapevine, Triggering Immune Responses and Detoxification of Fungal Phytotoxins

JOURNAL=Frontiers in Plant Science

VOLUME=10

YEAR=2019

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2019.00025

DOI=10.3389/fpls.2019.00025

ISSN=1664-462X

ABSTRACT=<p>Plant pathogens have evolved various strategies to enter hosts and cause diseases. Particularly <italic>Neofusicoccum parvum</italic>, a member of Botryosphaeria dieback consortium, can secrete the phytotoxins (-)-terremutin and (<italic>R</italic>)-mellein during grapevine colonization. The contribution of phytotoxins to Botryosphaeria dieback symptoms still remains unknown. Moreover, there are currently no efficient control strategies of this disease, and agro-environmental concerns have raised increasing interest in biocontrol strategies to limit disease spread in vineyards, especially by using some promising beneficial bacteria. Here, we first examined <italic>in planta</italic> the biocontrol capacity of <italic>Bacillus subtilis</italic> PTA-271 against <italic>N. parvum Np</italic>-Bt67 strain producing both (-)-terremutin and (<italic>R</italic>)-mellein. We then focused on the direct effects of PTA-271 on pathogen growth and the fate of pure phytotoxins, and explored the capacity of PTA-271 to induce or prime grapevine immunity upon pathogen infection or phytotoxin exposure. Results provided evidence that PTA-271 significantly protects grapevine cuttings against <italic>N. parvum</italic> and significantly primes the expression of <italic>PR2</italic> (encoding a β-1,3-glucanase) and <italic>NCED2</italic> (9-<italic>cis</italic>-epoxycarotenoid dioxygenase involved in abscisic acid biosynthesis) genes upon pathogen challenge. Using <italic>in vitro</italic> plantlets, we also showed that PTA-271 triggers the expression of salicylic acid- and jasmonic acid-responsive genes, including <italic>GST1</italic> (encoding a glutathione-<italic>S</italic>-transferase) involved in detoxification process. However, in PTA-271-pretreated plantlets, exogenous (-)-terremutin strongly lowered the expression of most of upregulated genes, except <italic>GST1</italic>. Data also indicated that PTA-271 can detoxify both (-)-terremutin and (<italic>R</italic>)-mellein and antagonize <italic>N. parvum</italic> under <italic>in vitro</italic> conditions. Our findings highlight (-)-terremutin and (<italic>R</italic>)-mellein as key aggressive molecules produced by <italic>N. parvum</italic> that may weaken grapevine immunity to promote Botryosphaeria dieback symptoms. However, PTA-271 can efficiently attenuate Botryosphaeria dieback by enhancing some host immune responses and detoxifying both phytotoxins produced by <italic>N. parvum</italic>.</p>