The gene of a GPI-anchoring protein a promising new target for the control of the cucurbit powdery mildew Podosphaera xanthii.

One of the main limitations of the cucurbit crops production is the powdery mildew disease, caused by the biotrophic fungus Podosphaera xanthii. An integrated management, using several strategies, is carried to control the disease but the application of fungicides is the most effective one. The problem is that P. xanthii has been classified by the Fungicide Resistance Action Committee (FRAC) as a pathogen with a high risk of resistance developing, in addition of the strong restrictions on the use of phytosanitary products at a European level. For this reason, new phytosanitary tools are necessary to allow a sustainable control of this devastating disease such as the use of the RNA interference (RNAi) technology. In this work, dsRNA targeting a P. xanthii gene, which encodes a protein that appears to be essential for the correct assembly of the fungal cell wall, was evaluated. Preliminary gene silencing results have shown a significant reduction of fungal development on melon plants suggesting that this gene may be a promising target for the control of powdery mildew of cucurbits. This work has been funded by AEI (PID2019-107464RB-C21).Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

El gen que produce una proteína de pared celular con anclaje a GPI, una nueva oportunidad para controlar Podosphaera xanthii.

Una de las principales limitaciones en la producción del cultivo de cucurbitáceas es la producida por la enfermedad del oídio, causada por el hongo biotrofo Podosphaera xanthii. Para controlar la enfermedad, se lleva a cabo un manejo integrado combinando distintas estrategias, siendo la aplicación de fungicidas el método más utilizado y eficaz. Sin embargo, P. xanthii ha sido catalogado por el Fungicide Resistance Action Commitee (FRAC) como un patógeno con un alto riesgo de desarrollo de resistencia al poco tiempo de ser estos compuestos autorizados para su uso. Si a ello le sumamos las nuevas restricciones que estos productos fitosanitarios están teniendo a nivel europeo, debido a la estrategia “de la granja a la mesa” dentro del Pacto Verde Europeo, nuevas herramientas fitosanitarias que permitan un control sostenible de esta enfermedad son necesarias. Es por ello que el empleo de tecnologías emergentes como el ARNi mediante el silenciamiento génico inducido por pulverización (SIGS), está atrayendo cada vez más el interés de empresas agrobiotecnológicas. En este trabajo se ha evaluado si el gen Ecm33 de P. xanthii, que codifica para una proteína de anclaje a glicosilfosfatidilinositol (GPI) que parece ser fundamental para el correcto ensamblaje de la pared celular fúngica, podría ser un gen esencial para el desarrollo de P. xanthii. Los resultados preliminares obtenidos tras pulverizar ARNdc dirigidos a silenciar la expresión de PxEcm33 sobre plantas de melón inoculadas con conidios de P. xanthii, han mostrado una reducción significativa del desarrollo fúngico. Estos resultados sugieren que el gen Ecm33 puede ser una diana prometedora para el control del oídio de las cucurbitáceas.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

RNAi Technology: A New Path for the Research and Management of Obligate Biotrophic Phytopathogenic Fungi

Powdery mildew and rust fungi are major agricultural problems affecting many economically important crops and causing significant yield losses. These fungi are obligate biotrophic parasites that are completely dependent on their hosts for growth and reproduction. Biotrophy in these fungi is determined by the presence of haustoria, specialized fungal cells that are responsible for nutrient uptake and molecular dialogue with the host, a fact that undoubtedly complicates their study under laboratory conditions, especially in terms of genetic manipulation. RNA interference (RNAi) is the biological process of suppressing the expression of a target gene through double-stranded RNA that induces mRNA degradation. RNAi technology has revolutionized the study of these obligate biotrophic fungi by enabling the analysis of gene function in these fungal. More importantly, RNAi technology has opened new perspectives for the management of powdery mildew and rust diseases, first through the stable expression of RNAi constructs in transgenic plants and, more recently, through the non-transgenic approach called spray-induced gene silencing (SIGS). In this review, the impact of RNAi technology on the research and management of powdery mildew and rust fungi will be addressed.Partial funding for open access charge: Universidad de Málag

Polyhydroxyalkanoate production by the plant beneficial rhizobacterium Pseudomonas chlororaphis PCL1606 influences survival and rhizospheric performance

Pseudomonas chlororaphis PCL1606 (PcPCL1606) is a model rhizobacterium used to study beneficial bacterial interactions with the plant rhizosphere. Many of its beneficial phenotypes depend on the production of the antifungal compound 2-hexyl, 5-propyl resorcinol (HPR). Transcriptomic analysis of PcPCL1606 and the dele-tional mutant in HPR production ΔdarB strain, assigned an additional regulatory role to HPR, and allowed the detection of differentially expressed genes during the bacterial interaction with the avocado rhizosphere. Interestingly, the putative genes phaG (PCL1606_46820) and phaI (PCL1606_56560), with a predicted role in polyhydroxyalkanoate biosynthesis, were detected to be under HPR control. Both putative genes were expressed in the HPR-producing wild-type strain, but strongly repressed in the derivative mutant ΔdarB, impaired in HPR production. Thus, a derivative mutant impaired in the phaG gene was constructed, characterized and compared with the wild-type strain PcPCL1606 and with the derivative mutant ΔdarB. The phaG mutant had strongly reduced PHA production by PcPCL1606, and displayed altered phenotypes involved in bacterial survival on the plant roots, such as tolerance to high temperature and hydrogen peroxide, and decreased root survival, in a similar way that the ΔdarB mutant. On the other hand, the phaG mutant does not have altered resistance to desiccation, motility, biofilm formation or adhesion phenotypes, as displayed by the HPR-defective ΔdarB mutant have. Interestingly, the mutant defective in PHA production also lacked a biocontrol phenotype against the soilborne pathogenic fungus Rosellinia necatrix, even when the derivative mutant still produced the antifungal HPR compound, demonstrating that the final biocontrol phenotype of PcPCL1606 first requires bacterial survival and adaptation traits to the soil and rhizosphere environment.Funding for open access charge: Universidad de Málaga / CBU