Molecular Pathogens 2024, Vol.15, No.5, 255-262 http://microbescipublisher.com/index.php/mp 257 required for engulfment and early spore coat formation. σG is activated in the prespore after engulfment and regulates the genes involved in the later stages of prespore development. At the final stage of sporulation, σK is activated in the mother cell, directing the expression of genes necessary for spore coat maturation and spore release (Figure 1) (Sun et al., 2021; Meeske et al., 2016). 3.3.2 Interactions between sigma factors and developmental pathways The activation and regulation of these sigma factors are highly coordinated and involve complex interactions between various proteins and regulatory pathways. For instance, the activation of pro-σK is a critical checkpoint in sporulation, ensuring that σK is only activated at the appropriate stage. This regulation involves proteolytic processing and other post-translational modifications that are essential for the proper timing and coordination of sporulation events (Al-Hinai et al., 2015). The acetylation of histone-like proteins such as HBsu has been shown to influence both the process of sporulation and the resistance properties of mature spores, highlighting the intricate regulatory mechanisms that govern spore formation and function. Figure 1 Activation of σK factor processing (Adopted from Sun et al., 2021) 4 Molecular Mechanisms Underlying Stress-Induced Sporulation 4.1 Integration of Stress Signals with Sporulation Pathways Bacillus subtilis integrates various stress signals to initiate sporulation, a process crucial for survival under adverse conditions. The alternative sigma factor SigB plays a pivotal role in this integration. SigB is activated through three distinct pathways responding to energy, environmental, and low-temperature stresses. Once activated, SigB induces the expression of Spo0E aspartyl-phosphatase, which inhibits the initiation of sporulation, thereby linking stress response and sporulation pathways. The phosphorylation of Spo0A, a key regulator of sporulation, is accelerated by a protein complex involving YlbF, YmcA, and YaaT, which also supports biofilm formation and the K-state, further integrating stress responses with developmental pathways (Dubnau et al., 2016; Zhu et al., 2024). 4.2 Role of small RNAs and regulatory networks in stress-responsive sporulation Small RNAs (sRNAs) and complex regulatory networks are integral to the stress-responsive sporulation in B. subtilis. The sRNA SR1, for instance, regulates the translation of kinA mRNA, which encodes a major histidine kinase in the sporulation phosphorelay. By inhibiting kinA translation, SR1 modulates the downstream targets of KinA/Spo0A, thereby influencing the timing and quality of sporulation. Deletion of sr1 accelerates sporulation but
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