Mechanisms for Desiccation Tolerance in Cyanobacterium Nostoc commune

活跃生长的细胞对风干特别敏感，大多数一暴露在大气中就会立即死亡。相比之下，一小群不同的原核生物和真核生物的成员有能力承受最严重的细胞缺水。它们是如何做到这一点的，仍然是生物学中一个耐人寻味的问题。发菜是一种蓝藻，具有显著的耐脱水能力，已被开发为无水生物原核细胞的模型。在干燥的情况下，公社细胞会合成水分胁迫多肽(WSP)，这些多肽约占总可溶性细胞蛋白的70%，约占干燥菌落干重的2%。WSP在风干状态下储存数十年的细胞中保持稳定。WSP在完全包裹细胞细丝的复合胞外多糖(EPS)内分泌和积累。在EPS中，WSP通过强烈的离子相互作用，与一种分泌的水溶性UV-A/B吸收色素(UVP)形成多聚体复合体。本研究的主要目的是：1)从发菜中分离WSP，并对其基因、其侧翼区域及其调控元件进行鉴定；2)了解WSP转录和WSP合成是如何受水分胁迫调节的；以及3)晶化WSP。微藻分泌的EPS和UVP代表了细胞在长期干燥过程中用来实现保护的两种策略。波茨博士发现的证据表明，WSP在这两种策略中的一种或两种中都发挥了作用。公社如何克服严重的细胞缺水的知识将提供对所有生物体中耐脱水的潜在机制的洞察。

Potts9513157Actively growing cells are particularly sensitive to air-drying and most die instantly upon exposure to the atmosphere. In contrast, the members of a small, diverse group of prokaryotic and eukaryotic organisms have the capacity to withstand the most acute of cell-water deficits. How they do so remains an intriguing problem in biology. One cyanobacterium, Nostoc Commune, has a marked capacity for desiccation tolerance and has been developed as a model for the anhydrobiotic prokaryotic cell. In response to air-drying cells of N. commune synthesize water stress polypeptides (Wsp) that constitute around 70% of the total soluble cell protein and approximately 2% of the dry weight of a desiccated colony. Wsp remain stable in cells stored for decades in the air-dried state. Wsp are secreted and accumulate within a complex extracellular polysaccharide (EPS) that completely envelops the cell filaments. Within the EPS the Wsp form multimeric complexes, through strong ionic interactions, with a secreted, water-soluble UV-A/B-absorbing pigment (UVP).The principle objectives of this study are: 1) to isolate wsp from Nostoc, and to characterize the gene, its flanking regions and its control elements; 2) to understand how wsp transcription and Wsp synthesis are regulated by water stress; and 3) to crystallize Wsp. The secretion of EPS and UVP by N. commune represent two strategies that the cells use to achieve protection during long-term desiccation. The evidence found by Dr. Potts suggests that Wsp play a role in one or both of these strategies. The knowledge of how N. commune overcomes acute cell-water deficit will provide an insight into the underlying mechanisms of desiccation tolerance in all organisms.