A Cladosporium strain 550W1 isolated from Lushan Russet Potato confers plant growth-promoting activity

Plant growth-promoting microorganisms (PGPMs) represent valuable biological resources for sustainable agriculture, and the discovery and functional characterization of new PGPM strains are therefore highly desirable. In this study, fungal strain 550W1 was isolated from tubers of Lushan Russet potato. Phenotypic assays confirmed that 550W1 promotes the growth of diverse plant hosts, including potato, Arabidopsis thaliana, soybean and the model legume Medicago truncatula. Our results suggested that 550W1 promoting plant growth may through biosynthesis and secretion of the phytohormones IAA, GA and CTK, and release of growth-regulating volatile organic compounds (VOCs). Strain 550W1 possesses remarkable halotolerance and broad pH adaptability ranging from pH 4.0 to 11.0. Morphological observation and ITS rDNA phylogenetic analysis preliminarily assigned it to Cladosporium sp., closely related to C. halotolerans. We performed hybrid whole-genome sequencing integrating Illumina short reads and Nanopore long reads. The estimated genome size of 550W1 is 31.27 Mb, while final assembly totals 28.49 Mb with 97.8% BUSCO completeness, indicative of high assembly quality. Genomic annotation identified biosynthetic gene clusters for phytohormone synthesis, NRPS clusters for siderophore production, and abundant stress-resistance genes. Multilocus sequence analyses (MLSA) of six markers produced result consistent with single-locus ITS phylogeny, by contrast, phylogenomic analysis and average nucleotide identity (ANI) calculations revealed that 550W1 clusters more closely with C. endophyticum. Given this incongruence, we designate this isolate Cladosporium sp. 550W1. Collectively, our findings demonstrate that Cladosporium sp. 550W1 functions as a novel PGPM strain to boost host plant performance.