Infection by dsRNA viruses is associated with enhanced sporulation efficiency in Saccharoymces cerevisiae

Upon starvation, diploid cells of the facultative sexual yeast Saccharoymces cerevisiae undergo sporulation, forming four metabolically quiescent and robust haploid spores encased in a degradable ascus. All endosymbionts, whether they provide net benefits or costs, utilise host resources; in yeast, this should induce an earlier onset of sporulation. Here, we tested whether the presence of endosymbiotic dsRNA viruses (M satellite and L-A helper) correspond with higher sporulation rate of their host, S. cerevisiae. We find that S. cerevisiae hosting both the M and L-A viruses (so-called “killer yeasts”) have significantly higher sporulation efficiency than those without. We also found that the removal of the M virus did not reduce sporulation frequency, possibly because the L-A virus still utilises host resources with and without the M virus. Our findings indicate that either virulent resource use by endosymbionts induces sporulation, or that viruses are spread more frequently to sporulating strains. Further exploration is required to distinguish cause from effect.

当处于饥饿胁迫时，兼性有性生殖酵母酿酒酵母（Saccharomyces cerevisiae）的二倍体细胞会启动孢子形成过程，生成四个代谢静默且抗逆性优异的单倍体孢子，这些孢子被包裹在可降解的子囊（ascus）中。
所有内共生体（endosymbiont）无论为宿主带来净收益还是净成本，均会利用宿主资源；在酵母体系中，这一过程理应诱发孢子形成的提前启动。
本研究旨在探究：携带内共生双链RNA（dsRNA）病毒——即M卫星病毒与L-A辅助病毒——的酿酒酵母宿主，其孢子形成率是否更高。
研究结果显示，同时携带M病毒与L-A病毒的菌株（即所谓"杀伤性酵母"），其孢子形成效率显著高于未携带该类病毒的菌株。
本研究同时发现，移除M病毒并不会降低孢子形成频率，这可能是因为无论是否存在M病毒，L-A病毒都会持续利用宿主资源。
本研究结果表明，要么是内共生体通过掠夺性资源利用诱发了孢子形成，要么是病毒更易传播至处于孢子形成阶段的菌株。若要明确二者的因果关系，仍需开展进一步的探索研究。