Biology subjects

Quiroz Monnens, T.

Publications and source records attributed to Quiroz Monnens, T..

2 recordsLinked to original sources

bioRxiv2024

Comparative transcriptomics reveal a highly polymorphic Xanthomonas HrpG virulence regulon

Bacteria of the genus Xanthomonas cause economically significant diseases in various crops. Their virulence is dependent on the translocation of type III effectors (T3Es) into plant cells by the type III secretion system (T3SS), a process regulated by the master response regulator HrpG. Although HrpG has been studied for over two decades, its regulon across diverse Xanthomonas species, particularly beyond type III secretion, remains understudied. In this study, we conducted transcriptome sequencing to explore the HrpG regulons of 17 Xanthomonas strains, encompassing six species and nine pathovars, each exhibiting distinct host and tissue specificities. We employed constitutive expression of plasmid-borne hrpG*, which encodes a constitutively active form of HrpG, to induce the regulon. Our findings reveal substantial inter- and intra-specific diversity in the HrpG* regulons across the strains. Besides 21 genes directly involved in the biosynthesis of the T3SS, the core HrpG* regulon is limited to only five additional genes encoding the transcriptional activator HrpX, the two T3E proteins XopR and XopL, a major facility superfamily (MFS) transporter, and the phosphatase PhoC. Interestingly, genes involved in chemotaxis and genes encoding enzymes with carbohydrate-active and proteolytic activities are variably regulated by HrpG*. The diversity in the HrpG* regulon suggests that HrpG-dependent virulence in Xanthomonas might be achieved through several distinct strain-specific strategies, potentially reflecting adaptation to diverse ecological niches. These findings enhance our understanding of the complex role of HrpG in regulating various virulence and adaptive pathways, extending beyond T3Es and the T3SS. IMPORTANCEIn the decades since its discovery, HrpG and its role in the regulation of the type III secretion system (T3SS) and its associated type III effectors (T3Es) in Xanthomonas has been the subject of extensive research. Despite notable progress in understanding its molecular regulatory mechanisms, the full spectrum of processes under control of HrpG, particularly beyond the T3SS and T3Es, and the degree of regulatory conservation across plant-pathogenic Xanthomonas species, remained unclear. To address this knowledge gap, we systematically compared the transcriptomes of 17 Xanthomonas strains, expressing a constitutively active form of HrpG, called HrpG*. We showed that HrpG* regulates different physiological processes other than the T3SS and T3Es and that this regulation shows substantial variation across the different strains. Taken together, our results provide new insights into Xanthomonas-plant interactions through the regulation of different metabolic and virulence pathways by the master response regulator HrpG.

microbiology↗

bioRxiv2021

Sexual reproduction contributes to the evolution of resistance breaking isolates of the spinach pathogen Peronospora effusa

Peronospora effusa causes downy mildew, the economically most important disease of cultivated spinach worldwide. To date, 19 P. effusa races have been denominated based on their capacity to break spinach resistances, but their genetic diversity and the evolutionary processes that contribute to race emergence are unknown. Here, we performed the first systematic analysis of P. effusa races showing that those emerge by both asexual and sexual reproduction. Specifically, we studied the diversity of 26 P. effusa isolates from 16 denominated races based on mitochondrial and nuclear comparative genomics. Mitochondrial genomes based on long-read sequencing coupled with diversity assessment based on short-read sequencing uncovered two mitochondrial haplogroups, each with distinct genome organization. Nuclear genome-wide comparisons of the 26 isolates revealed that ten isolates from six races could clearly be divided into three asexually evolving groups, in concordance with their mitochondrial phylogeny. The remaining isolates showed signals of reticulated evolution and discordance between nuclear and mitochondrial phylogenies, suggesting that these evolved through sexual reproduction. Increased understanding of this pathogens reproductive modes will provide the framework for future studies into the molecular mechanisms underlying race emergence and into the P. effusa-spinach interaction, thus assisting in sustainable production of spinach through knowledge-driven resistance breeding. Significance statementMany microbial plant pathogens depend on the successful colonization of their hosts to complete their life cycle, thereby damaging food crops worldwide. The most effective way of disease control is to deploy genetic disease resistances. However, the extensive use of resistant crop varieties exerts strong selective pressure on microbial plant pathogens to adapt in order to escape resistance. Through yet unknown mechanisms, the spinach pathogen Peronospora effusa can rapidly break the resistance of newly introduced varieties, often within a single growing season. Thus, there is an urgent need to better understand the mechanisms driving adaptation in P. effusa. This information will lead the way to knowledge-driven resistance breeding. Here, we capture for the first time the genetic variation of 26 P. effusa, 16 of which can break a different combination of host resistances. We demonstrate that P. effusa isolates evolve by both asexual and sexual reproduction, and thereby provide the framework to study the molecular mechanisms of the interactions between P. effusa and spinach.

evolutionary biology↗