Population Genomics Reveals Population Structure and Mating-Type Loci in Marssonina brunnea

Clonal genomic population structure of Beauveria brongniartii and Beauveria pseudobassiana: Pathogens of the common European cockchafer (Melolontha melolontha L.)

Beauveria brongniartii is a fungal pathogen that infects the beetle Melolontha melolontha, a significant agricultural pest in Europe. While research has primarily focused on the use of B. brongniartii for controlling M. melolontha, the genomic structure of the B. brongniartii population remains unknown. This includes whether its structure is influenced by its interaction with M. melolontha, the timing of beetle-swarming flights, geographical factors, or reproductive mode. To address this, we analysed genome-wide SNPs to infer the population genomics of Beauveria spp., which were isolated from infected M. melolontha adults in an Alpine region. Surprisingly, only one-third of the isolates were identified as B. brongniartii, while two-thirds were distributed among cryptic taxa within B. pseudobassiana, a fungal species not previously recognized as a pathogen of M. melolontha. Given the prevalence of B. pseudobassiana, we conducted analyses on both species. We found no spatial or temporal genomic patterns within either species and no correlation with the population structure of M. melolontha, suggesting that the dispersal of the fungi is independent of the beetle. Both species exhibited clonal population structures, with B. brongniartii fixed for one mating type and B. pseudobassiana displaying both mating types. This implies that factors other than mating compatibility limit sexual reproduction. We conclude that the population genomic structure of Beauveria spp. is primarily influenced by predominant asexual reproduction and dispersal.

Heterologous expression of Arabidopsis pattern recognition receptor RLP23 increases broad-spectrum resistance in poplar to fungal pathogens

The pattern recognition receptor AtRLP23 from Arabidopsis thaliana recognizes the epitopes (nlp24s) of necrosis and ethylene-inducing peptide 1-like proteins (NLPs) and triggers pattern-triggered immunity (PTI). Here, we established methods for studying the early events of PTI in the hybrid poplar cultivar Shanxin (Populus davidiana × Populus bolleana) in response to the flagellin epitope. We confirmed that wild-type Shanxin cannot generate PTI responses on nlp24 treatment. Four NLP homologues were characterized from two common fungal pathogens of Shanxin, namely Marssonina brunnea f. sp. monogermtubi (MbMo) and Elsinoë australis (Ea), which cause black leaf spot and anthracnose disease, respectively, and the nlp24s of three of them could be responded to by Nicotiana benthamiana leaves expressing AtRLP23. We then created AtRLP23 transgenic Shanxin lines and confirmed that the heterologous expression of AtRLP23 conferred on transgenic Shanxin the ability to respond to one nlp24 of each fungal pathogen. Consistently, infection assays with MbMo or Ea showed obviously lower levels of disease symptoms and significantly inhibited the growth of fungi on the transgenic poplar compared with that in wild-type poplar. Overall, our results indicated that the heterologous expression of AtRLP23 allowed transgenic Shanxin to generate a PTI response to nlp24s, resulting in increased broad-spectrum fungal disease resistance.