Antagonismo enzimático de Trichoderma spp., sobre Phytophthora parasitica y Fusarium oxysporum en jamaica (Hibiscus sabdariffa L.)

México es el séptimo productor de jamaica (Hibiscus sabdariffa), y el estado de Guerrero concentra más del 70 % de la producción nacional. El cultivo presenta limitantes fitosanitarias importantes, destacando la “pata prieta” asociada a un complejo de patógenos (Fusarium oxysporum y Phytophthora parasitica), con pérdidas de hasta 100 % en áreas sin manejo fitosanitario. Debido a la naturaleza del consumo del producto final, es necesaria la implementación de estrategias ecológicas de manejo de la enfermedad. El objetivo del estudio fue cuantificar la actividad de quitinasas y glucanasas de aislados Trichoderma spp., y evaluar su efecto inhibitorio in vitro sobre F. oxysporum y P. parasitica. Se evaluaron las cepas Ta10, Ta11, Ta6 y Ta9 de T. asperellum y Ti14 de T. inhamatum provenientes de suelos cultivados con jamaica y alta incidencia de los patógenos. Los niveles de quitinasas y glucanasas en todos los aislados de Trichoderma spp. fueron significativos (P£0,05); la cepa Ta9 mostró la mayor actividad específica de quitinasas, y la cepa Ti14 la mayor de glucanasas. Todos los filtrados provenientes de los diferentes aislados de Trichoderma spp. generaron una inhibición sustancial del crecimiento micelial de F. oxysporum y P. parasitica. De manera consistente, la cepa Ta9 alcanzó porcentajes de inhibición mayores al 90 % en ambos ensayos. Se detectó correlación significativa entre la actividad enzimática y la inhibición del crecimiento de los aislados de Trichoderma spp. sobre los agentes patógenos.

Diverse Trajectories Drive the Expression of a Giant Virus in the Oomycete Plant Pathogen Phytophthora parasitica

Giant viruses of amoebas, recently classified in the class Megaviricetes, are a group of viruses that can infect major eukaryotic lineages. We previously identified a set of giant virus sequences in the genome of Phytophthora parasitica, an oomycete and a devastating major plant pathogen. How viral insertions shape the structure and evolution of the invaded genomes is unclear, but it is known that the unprecedented functional potential of giant viruses is the result of an intense genetic interplay with their hosts. We previously identified a set of giant virus sequences in the genome of P. parasitica, an oomycete and a devastating major plant pathogen. Here, we show that viral pieces are found in a 550-kb locus and are organized in three main clusters. Viral sequences, namely RNA polymerases I and II and a major capsid protein, were identified, along with orphan sequences, as a hallmark of giant viruses insertions. Mining of public databases and phylogenetic reconstructions suggest an ancient association of oomycetes and giant viruses of amoeba, including faustoviruses, African swine fever virus (ASFV) and pandoraviruses, and that a single viral insertion occurred early in the evolutionary history of oomycetes prior to the Phytophthora–Pythium radiation, estimated at ∼80 million years ago. Functional annotation reveals that the viral insertions are located in a gene sparse region of the Phytophthora genome, characterized by a plethora of transposable elements (TEs), effectors and other genes potentially involved in virulence. Transcription of viral genes was investigated through analysis of RNA-Seq data and qPCR experiments. We show that most viral genes are not expressed, and that a variety of mechanisms, including deletions, TEs insertions and RNA interference may contribute to transcriptional repression. However, a gene coding a truncated copy of RNA polymerase II along a set of neighboring sequences have been shown to be expressed in a wide range of physiological conditions, including responses to stress. These results, which describe for the first time the endogenization of a giant virus in an oomycete, contribute to challenge our view of Phytophthora evolution.

Susceptibility factor RTP1 negatively regulates Phytophthora parasitica resistance via modulating UPR regulators bZIP60 and bZIP28

The unfolded protein response (UPR) is a conserved stress adaptive signaling pathway in eukaryotic organisms activated by the accumulation of misfolded proteins in the endoplasmic reticulum (ER). UPR can be elicited in the course of plant defense, playing important roles in plant–microbe interactions. The major signaling pathways of plant UPR rely on the transcriptional activity of activated forms of ER membrane-associated stress sensors bZIP60 and bZIP28, which are transcription factors that modulate expression of UPR genes. In this study, we report the plant susceptibility factor Resistance to Phytophthora parasitica 1 (RTP1) is involved in ER stress sensing and rtp1-mediated resistance against P. parasitica is synergistically regulated with UPR, as demonstrated by the simultaneous strong induction of UPR and ER stress-associated immune genes in Arabidopsis thaliana rtp1 mutant plants during the infection by P. parasitica. We further demonstrate RTP1 contributes to stabilization of the ER membrane-associated bZIP60 and bZIP28 through manipulating the bifunctional protein kinase/ribonuclease IRE1-mediated bZIP60 splicing activity and interacting with bZIP28. Consequently, we find rtp1bzip60 and rtp1bzip28 mutant plants exhibit compromised resistance accompanied with attenuated induction of ER stress-responsive immune genes and reduction of callose deposition in response to P. parasitica infection. Taken together, we demonstrate RTP1 may exert negative modulating roles in the activation of key UPR regulators bZIP60 and bZIP28, which are required for rtp1-mediated plant resistance to P. parasitica. This facilitates our understanding of the important roles of stress adaptive UPR and ER stress in plant immunity.