Kim Junwon, Rose Mark D
Department of Molecular Biology, Princeton University, Princeton, New Jersey, United States of America.
PLoS Genet. 2015 Dec 7;11(12):e1005684. doi: 10.1371/journal.pgen.1005684. eCollection 2015 Dec.
Upon nutrient limitation, budding yeasts like Saccharomyces cerevisiae can be induced to adopt alternate filament-like growth patterns called diploid pseudohyphal or invasive haploid growth. Here, we report a novel constitutive pseudohyphal growth state, sharing some characteristics with classic forms of filamentous growth, but differing in crucial aspects of morphology, growth conditions and genetic regulation. The constitutive pseudohyphal state is observed in fus3 mutants containing various septin assembly defects, which we refer to as sadF growth (septin assembly defect induced filamentation) to distinguish it from classic filamentation pathways. Similar to other filamentous states, sadF cultures comprise aggregated chains of highly elongated cells. Unlike the classic pathways, sadF growth occurs in liquid rich media, requiring neither starvation nor the key pseudohyphal proteins, Flo8p and Flo11p. Moreover sadF growth occurs in haploid strains of S288C genetic background, which normally cannot undergo pseudohyphal growth. The sadF cells undergo highly polarized bud growth during prolonged G2 delays dependent on Swe1p. They contain septin structures distinct from classical pseudo-hyphae and FM4-64 labeling at actively growing tips similar to the Spitzenkörper observed in true hyphal growth. The sadF growth state is induced by synergism between Kss1p-dependent signaling and septin assembly defects; mild disruption of mitotic septins activates Kss1p-dependent gene expression, which exacerbates the septin defects, leading to hyper-activation of Kss1p. Unlike classical pseudo-hyphal growth, sadF signaling requires Ste5, Ste4 and Ste18, the scaffold protein and G-protein β and γ subunits from the pheromone response pathway, respectively. A swe1 mutation largely abolished signaling, breaking the positive feedback that leads to amplification of sadF signaling. Taken together, our findings show that budding yeast can access a stable constitutive pseudohyphal growth state with very few genetic and regulatory changes.
在营养限制条件下，像酿酒酵母这样的出芽酵母可被诱导采用称为二倍体假菌丝或侵入性单倍体生长的交替丝状生长模式。在此，我们报告了一种新的组成型假菌丝生长状态，它与经典丝状生长形式有一些共同特征，但在形态、生长条件和基因调控的关键方面有所不同。组成型假菌丝状态在含有各种隔膜蛋白组装缺陷的fus3突变体中观察到，我们将其称为sadF生长（隔膜蛋白组装缺陷诱导的丝状化），以将其与经典丝状化途径区分开来。与其他丝状状态类似，sadF培养物由高度细长细胞的聚集链组成。与经典途径不同，sadF生长发生在富含液体的培养基中，既不需要饥饿也不需要关键的假菌丝蛋白Flo8p和Flo11p。此外，sadF生长发生在S288C遗传背景的单倍体菌株中，这些菌株通常不能进行假菌丝生长。sadF细胞在依赖Swe1p的长时间G2期延迟期间经历高度极化的芽生长。它们含有与经典假菌丝不同的隔膜蛋白结构，并且在活跃生长的尖端有FM4 - 64标记，类似于在真正菌丝生长中观察到的Spitzenkörper。sadF生长状态由Kss1p依赖性信号传导和隔膜蛋白组装缺陷之间的协同作用诱导；有丝分裂隔膜蛋白的轻度破坏激活Kss1p依赖性基因表达，这会加剧隔膜蛋白缺陷，导致Kss1p的过度激活。与经典假菌丝生长不同，sadF信号传导分别需要来自信息素反应途径的支架蛋白Ste5、G蛋白β和γ亚基Ste4和Ste18。swe1突变在很大程度上消除了信号传导，打破了导致sadF信号放大的正反馈。综上所述，我们的研究结果表明，出芽酵母只需很少的遗传和调控变化就能进入稳定的组成型假菌丝生长状态。
