The Crucial Role of LTTR_0390 in <i>Burkholderia gladioli</i> BBB-01 in Orchestrating Antibiotic Production, Quorum-Sensing Responses, and Pathogenicity on Mushrooms

<i>Burkholderia gladioli</i> strain BBB-01, classified as <i>B. gladioli</i> pv <i>agaricicola</i>, displays broad antagonism against diverse pathogens. We investigated the regulatory role of the LysR-type transcriptional regulator LTTR_0390 and its potential involvement in pathogenicity toward the cultivated button mushroom (<i>Agaricus bisporus</i>). Using insertional mutagenesis, metabolite profiling, transcriptomic analysis, and phenotypic assays, we found that disruption of the <i>lttr_0390</i> gene extensively reprograms secondary metabolism, for example, upregulating the gladiostatin biosynthetic gene cluster while downregulating the gladiolin cluster. Although this gene disruption did not affect production of quorum-sensing (QS) autoinducers, the mutant exhibited reduced QS-linked behaviors, including motility and biofilm formation. Additionally, disruption of <i>lttr_0390</i> markedly diminished soft rot symptoms on <i>A. bisporus</i> fruiting bodies. Together, these findings identify LTTR_0390 as a global regulator that coordinates secondary metabolism and QS-linked behaviors while decoupling antifungal activity from mushroom damage.