Transcription factor Ste12 regulates the spore maturation and proliferation of silkworm microsporidium Nosema bombycis.

Background: As the first identified microsporidium, Nosema bombycis can infect silkworm Bombyx mori to cause pebrine which brings huge economic losses to sericulture all over the world. The life cycle of Nosema bombycis is divided into three phases, including the infective phase, the proliferative phase and the sporogonic phase. The factor(s) that regulate spore maturation of Nosema bombycis is still unknown. Ste12 is a fungi-specific transcription factor that plays an important regulatory role in fungal development and pathogenicity. The purpose of this study is to elucidate the function of Ste12 homologous (NbSte12) in Nosema bombycis.

Results: Here, we analyzed the transcription and subcellular localization characteristics of NbSte12. It was mainly expressed in the nucleus of the immature spores, and NbSte12 had the transcriptional activation activity, with its C-terminal necessary for this ability. DNA affinity purification sequencing (DAP-seq) analysis revealed that the genes regulated by NbSte12 were involved in spore maturation, cell division, and energy metabolism. The knockdown of NbSte12 gene resulted in the decrease of chitin layer thickness, spore germination activity and proliferation. Then, electrophoretic mobility shift assay (EMSA) and quantitative reverse transcription polymerase chain reaction (RT-qPCR) analyses showed that NbSte12 could bind to the promoters of the CHS7, SWP26, SWP30, PTP1 and PTP2 genes, which are involved in spore wall and polar tube formation, thereby positively regulating their transcription.

Conclusions: NbSte12 plays an indispensable role in the formation of chitin layer, spore germination and proliferation, thus regulating the development and maturation of microsporidium Nosema bombycis. © 2025 Society of Chemical Industry.