Biology subjects

Chavez, S. M.

Publications and source records attributed to Chavez, S. M..

5 recordsLinked to original sources

bioRxiv2025

PCR-based specific detection of multiple Nigrospora species causing a banana leaf spot disease

The genus Nigrospora has been identified as the primary causative agent of leaf spot disease in banana plantations in Mindanao, the Philippines. The symptoms caused by Nigrospora species are similar to those of black leaf streak disease (black sigatoka), which has made managing the disease challenging. Furthermore, development of rapid and precise molecular diagnostic methodologies for leaf spot disease has remained elusive. In the present study, a polymerase chain reaction (PCR)-based detection system was developed. The system targets a Nigrospora-specific genomic region, which was identified through comparative analysis of the genus Nigrospora and related genera. The newly designed primer set nigF/nigR specifically detected six pathogenic Nigrospora species associated with banana leaf spot disease (N. chinensis, N. lacticolonia, N. nigrocolonia, N. singularis, N. sphaerica, and N. vesicularifera), while no amplicon was observed for 15 non-Nigrospora species, including Pseudocercospora fijiensis isolated from banana leaves. The results indicate that the primers enable clear differentiation from other genera, including the important pathogen P. fijiensis. The primers also detected diverse Nigrospora isolates (N. banbusae, N. chinensis, N. musae, N. oryzae, N. sphaerica, and N. rubi) obtained from different hosts and regions within Japan, demonstrating broad applicability. Sensitivity testing demonstrated the capacity to detect as minimal as 10 pg of genomic DNA. Additionally, a pathogenic Nigrospora isolate was detected successfully from infected banana tissue. This study presents a novel molecular diagnostic tool for Nigrospora species, offering a rapid, specific, and practical approach, which could enhance evidence-based disease management in epidemiological investigations and banana production systems.

molecular biology↗

bioRxiv2025

Outbreak of leaf spot disease of Cavendish banana caused by Nigrospora spp. in Mindanao Island, Philippines

Banana leaf diseases are a significant threat to Cavendish banana production. In the Philippines, the main disease has been diagnosed as Black sigatoka disease caused by Pseudocercospora fijiensis based on symptoms. However, our study showed that the main pathogen in Mindanao island, the largest banana-producing region in the Philippines, belongs to the genus Nigrospora, contradicting previous assumptions. We clarified the phylogenetic positions of 160 Nigrospora isolates based on molecular phylogenetic analyses using ITS, {beta}-tubulin, and tef1 sequences, and compared their morphology with known species. Molecular phylogenetic and morphological analysis revealed that Nigrospora isolates comprised N. chinensis, N. lacticolonia, N. cf. singularis, N. sphaerica, N. vesicularifera, and a novel species, N. nigrocolonia. Pathogenicity tests on banana leaves confirmed that these species are pathogenic. Species other than N. sphaerica were for the first time reported as pathogens of banana leaf. The results of the fungicide sensitivity test using 14 fungicides, including pyrimethanil, spiroxamine, and tebuconazole, for the Sigatoka disease showed 100% inhibition of all isolates at 100 ppm of active ingredients. However, low-sensitivity isolates were observed for the remaining 11 fungicides. Our findings indicated the need for a comprehensive review of banana leaf disease prevention strategies.

molecular biology↗

bioRxiv2022

Type I IFN signaling mediates NET release to promote Mycobacterium tuberculosis replication and granuloma caseation

Neutrophils are the most abundant cell type in airways of tuberculosis patients. Recent investigations reported induction of neutrophil extracellular traps (NETs) during Mycobacterium tuberculosis (Mtb) infection, however, the molecular regulation and impact of NETosis on Mtb pathogenesis is unknown. We find that in response to Mtb infection in neutrophils, PAD4 citrullinates histones to decondense chromatin that gets packaged into vesicles for release as NETs in a manner that can maintain neutrophil viability and promote Mtb replication. Type I interferon, which has been associated with NETosis in numerous contexts but without a known mechanism, promotes formation of chromatin-containing vesicles and NET release. Analysis of nonhuman primate granulomas supports a model where neutrophils are exposed to type I interferon from macrophages as they migrate into the granuloma, where they release NETs that contribute to necrosis and caseation. Our data reveals NETosis as a promising target to inhibit Mtb replication and granuloma caseation.

microbiology↗

bioRxiv2022

Autophagy protects against high-dose Mycobacterium tuberculosis infection

Host autophagy had been associated with the control of Mycobacterium tuberculosis (Mtb) infection due to its ability to sequesters microorganisms through a process termed "xenophagy"1-4. Xenophagy purportedly limits Mtb replication within infected macrophages1-4. However, studies in mice using a standard low-dose infection model demonstrated that xenophagy in infected phagocytes is not required to control Mtb pathogenesis5,6. Instead, an autophagy-independent function of ATG5 in myeloid cells controls low-dose Mtb infection through limiting neutrophilic inflammation5. Hitherto, an in vivo role for autophagy during Mtb infection remained to be elucidated. We report herein that autophagy in myeloid cells mediates protection against high-dose Mtb infection, providing the first evidence for a role for autophagy in myeloid cells during Mtb infection in vivo. With the exception of ATG5, the autophagy proteins required to control high-dose Mtb infection are dispensable for host defense against a standard low-dose Mtb infection. Specifically, autophagy is required in CD11c+ cells, but is dispensable in neutrophils, to control a high-dose Mtb infection in the lung. The role for autophagy is not to directly degrade Mtb in macrophages through xenophagy, but mainly to limit myeloid-derived suppressor cell accumulation and to promote sustained protective T cell responses. Together, our data highlight a novel role for autophagy in controlling Mtb infection, distinct from that of Atg5 during low-dose Mtb infection, or any previously reported roles for autophagy. In addition, our finding that the result of a pathogen-plus-susceptibility gene interaction is dependent on pathogen burden has important implications on our understanding of how Mtb infection in humans can lead to a spectrum of outcomes, the variables that contribute to autophagy gene function during infection and inflammation, and the potential use of autophagy modulators in clinical medicine.

microbiology↗

bioRxiv2022

Autophagy is required in macrophages and dendritic cells to prevent early recruitment of neutrophils during Mycobacterium tuberculosis infection

The immune response to Mycobacterium tuberculosis infection determines tuberculosis disease outcomes, yet we have an incomplete understanding of what immune factors contribute to a protective immune response. Neutrophilic inflammation has been associated with poor disease prognosis in humans and in animal models during M. tuberculosis infection and, therefore, must be tightly regulated. ATG5 is an essential autophagy protein that is required in innate immune cells to control neutrophil-dominated inflammation and promote survival during M. tuberculosis infection, however, the mechanistic basis for how ATG5 regulates neutrophil recruitment is unknown. To interrogate what innate immune cells require ATG5 to control neutrophil recruitment during M. tuberculosis infection, we used different mouse strains that conditionally delete Atg5 in specific cell types. We found that ATG5 is required in CD11c+ cells (lung macrophages and dendritic cells) to control the production of proinflammatory cytokines and chemokines during M. tuberculosis infection, which would otherwise promote neutrophil recruitment. This role for ATG5 is autophagy-dependent, but independent of mitophagy, LC3-associated phagocytosis, and inflammasome activation, which are the most well-characterized ways that autophagy proteins regulate inflammation. In addition to the increase in proinflammatory cytokine production during M. tuberculosis infection, loss of ATG5 in innate immune cells also results in an early induction of TH17 responses. Despite prior published in vitro cell culture experiments supporting a role for autophagy in controlling M. tuberculosis replication in macrophages, loss of autophagy does not affect M. tuberculosis burden in macrophages in vivo and, therefore, the effects of autophagy on inflammatory responses occur without changes in pathogen numbers. These findings reveal new roles for autophagy proteins in lung resident macrophages and dendritic cells that are required to suppress inflammatory responses that are associated with poor control of M. tuberculosis infection.

immunology↗