The GATA Transcription Factor NsdD Regulates Vegetative Growth, Asexual Sporulation, and Melanin Biosynthesis in <i>Colletotrichum siamense</i> and <i>C. graminicola</i>

The genus <i>Colletotrichum</i> infects over 3,000 monocot and dicot plant species, inflicting substantial economic losses globally. GATA zinc finger proteins play a pivotal role as transcription factors governing fungal growth and development. In this study, we characterized the GATA transcription factor NsdD in <i>C. siamense</i> (CsNsdD) and <i>C. graminicola</i> (CgrNsdD), respectively. Disruption of <i>CsnsdD</i> or <i>CgrnsdD</i> resulted in a reduced mycelial growth rate and sparse hyphal morphology. Functional characterization revealed that NsdD acted as a typical negative regulator of conidiation and melanin biosynthesis in both pathogens. Notably, the <i>CsnsdD</i> knockout mutant demonstrated precocious conidiation and increased conidial yield. Similarly, deletion of <i>CgrnsdD</i> led to enhanced production of both oval and falcate conidia while additionally promoting the formation of falcate conidia in a liquid culture. Furthermore, genetic disruption of <i>CsnsdD</i>/<i>CgrnsdD</i> substantially elevated melanin accumulation in mycelia. Pathogenicity assessment demonstrated that deletion of <i>CsnsdD/CgrnsdD</i> led to a marked attenuation of fungal virulence. Transcriptomic analysis revealed that both CsNsdD and CgrNsdD contribute to the regulation of multiple functional genes, including those associated with conidiation, the DHN (1,8-dihydroxynaphthalene) melanin biosynthesis pathway, and the production of cell wall-degrading enzymes. In summary, NsdD functions as a global transcriptional regulator in orchestrating vegetative growth, conidiation, and melanin biosynthesis in <i>C. siamense</i> and <i>C. graminicola</i>.