Genetic Manipulation of the Brassicaceae Smut Fungus Thecaphora thlaspeos

Identification and Characterization of an Antifungal Gene Mt1 from Bacillus subtilis by Affecting Amino Acid Metabolism in Fusarium graminearum

Fusarium head blight is a devastating disease that causes significant economic losses worldwide. Fusarium graminearum is a crucial pathogen that requires close attention when controlling wheat diseases. Here, we aimed to identify genes and proteins that could confer resistance to F. graminearum. By extensively screening recombinants, we identified an antifungal gene, Mt1 (240 bp), from Bacillus subtilis 330-2. We recombinantly expressed Mt1 in F. graminearum and observed a substantial reduction in the production of aerial mycelium, mycelial growth rate, biomass, and pathogenicity. However, recombinant mycelium and spore morphology remained unchanged. Transcriptome analysis of the recombinants revealed significant down-regulation of genes related to amino acid metabolism and degradation pathways. This finding indicated that Mt1 inhibited amino acid metabolism, leading to limited mycelial growth and, thus, reduced pathogenicity. Based on the results of recombinant phenotypes and transcriptome analysis, we hypothesize that the effect of Mt1 on F. graminearum could be related to the metabolism of branched-chain amino acids (BCAAs), the most affected metabolic pathway with significant down-regulation of several genes. Our findings provide new insights into antifungal gene research and offer promising targets for developing novel strategies to control Fusarium head blight in wheat.

Monitoring Tritrophic Biocontrol Interactions Between Bacillus spp., Fusarium oxysporum f. sp. cubense, Tropical Race 4, and Banana Plants in vivo Based on Fluorescent Transformation System

Bacillus spp. is effective biocontrol agents for Fusarium wilt of banana (FWB), tropical race 4 (TR4). This study explores the colonization by Bacillus subtilis, Bacillus velezensis, and Bacillus amyloliquefaciens of host banana plants and elucidates the mechanism of antagonistic TR4 biocontrol. The authors selected one B. subtilis strain, three B. velezensis strains, and three B. amyloliquefaciens strains that are proven to significantly inhibit TR4 in vitro, optimized the genetic transformation conditions and explored their colonization process in banana plants. The results showed that we successfully constructed an optimized fluorescent electro-transformation system (OD₆₀₀ of bacteria concentration=0.7, plasmid concentration=50ng/μl, plasmid volume=2μl, transformation voltage=1.8kV, and transformation capacitance=400Ω) of TR4-inhibitory Bacillus spp. strains. The red fluorescent protein (RFP)-labeled strains were shown to have high stability with a plasmid-retention frequency above 98%, where bacterial growth rates and TR4 inhibition are unaffected by fluorescent plasmid insertion. In vivo colonizing observation by Laser Scanning Confocal Microscopy (LSCM) and Scanning Electron Microscopy (SEM) showed that Bacillus spp. can colonize the internal cells of banana plantlets roots. Further, fluorescent observation by LSCM showed these RFP-labeled bacteria exhibit chemotaxis (chemotaxis ratio was 1.85±0.04) toward green fluorescent protein (GFP)-labeled TR4 hyphae in banana plants. We conclude that B. subtilis, B. velezensis, and B. amyloliquefaciens can successfully colonize banana plants and interact with TR4. Monitoring its dynamic interaction with TR4 and its biocontrol mechanism is under further study.

How Do Smut Fungi Use Plant Signals to Spatiotemporally Orientate on and In Planta?

Smut fungi represent a large group of biotrophic plant pathogens that cause extensive yield loss and are also model organisms for studying plant-pathogen interactions. In recent years, they have become biotechnological tools. After initial penetration of the plant epidermis, smut fungi grow intra-and intercellularly without disrupting the plant-plasma membrane. Following the colonialization step, teliospores are formed and later released. While some smuts only invade the tissues around the initial penetration site, others colonize in multiple plant organs resulting in spore formation distal from the original infection site. The intimate contact zone between fungal hyphae and the host is termed the biotrophic interaction zone and enables exchange of signals and nutrient uptake. Obviously, all steps of on and in planta growth require fine sensing of host conditions as well as reprogramming of the host by the smut fungus. In this review, we highlight selected examples of smut fungal colonization styles, directional growth in planta, induction of spore formation, and the signals required, pointing to excellent reviews for details, to draw attention to some of the open questions in this important research field.