Photoacclimation during senescence and the control of longevity in microalgae

衰老是所有生命的基本组成部分，但关于生物体衰老的原因和机制以及控制寿命的条件仍然存在相当大的争论。虽然衰老一直是多细胞生物体的浓厚兴趣，但人们意识到包括细菌在内的单细胞生物体的衰老让许多人感到惊讶。更令人惊讶的是，我们可以在实验室中延缓许多生物体的衰老，从而延长它们的寿命。一种简单但强有力的方法是通过减少他们饮食中的卡路里含量来做到这一点，这种方法被称为卡路里限制。我们建议用微藻系统--莱茵衣藻来研究衰老或“条件性衰老”的过程。随着细胞的生长，当营养物质耗尽时，它们达到最大细胞密度，进入有限生长时期，随后不可避免地进入死亡阶段。我们建议研究细胞在衰老过程中如何保护自己免受过多光照的影响。我们的目标是确定负责吸收光的蛋白质如何改变其组织，从高效的光吸收转换为作为热量的能量消耗，从而保护细胞免受损害并延长寿命。我们还建议研究微藻在培养中寿命的决定因素，以及参与控制反应的细胞途径。我们将研究基因的表达，以确定基因网络，这些基因网络可能提供线索，了解细胞如何应对衰老的挑战，以及改变介质的卡路里含量如何影响在这些条件下的生存。我们还建议在基因相同的微藻种群中检查个体之间的生化和生理差异，以检查在压力条件下长期生存的其他策略。最终，在需要大规模生产藻类的微藻生物燃料和生物产品工业中，关于用于在静止阶段生存、控制细胞密度和延长寿命的策略的知识将是有用的。对细胞生长和生存极限的理解最终将影响生产生物质和增加产量的方法。

Aging is a fundamental part of all life, yet there remains considerable debate as to the causes and mechanisms of why organisms age and the conditions that control longevity. While aging has been of intense interest in multicellular organisms, the realization that unicellular organisms age, including bacteria, has come to many as a surprise. Even more surprising, we can slow down ageing in many organisms in the lab such that they have a longer lifespan. A simple but robust way of doing this by reducing the calorie content of their diet, an approach called caloric restriction. We are proposing to study the process of aging or "conditional senescence" with a model, microalgal system-Chlamydomonas reinhardtii. As cells grow, they reach a maximum cell density as nutrients become depleted and enter a period of limited growth followed inevitably by a death phase. We are proposing to examine the way in which cells protect themselves from too much light as they age. Our goal is to determine how the proteins responsible for absorbing light change their organization to toggle from efficient light absorption to energy dissipation as heat, thereby protecting the cell from damage and extending longevity. We also propose to study the determinants of microalgal longevity in culture and the cellular pathways involved in controlling the response. We will examine the expression of genes to identify gene networks that may provide clues as to how cells meet the challenges of senescence and how altering caloric content of the media may affect survival under these conditions. We also propose to examine the biochemical and physiological differences between individuals in a microalgal population of genetically identical cells to examine additional strategies for long-term survival under stressful conditions. Ultimately, the knowledge on the strategies used to survive stationary phase, control cell density and extend longevity will be useful in the microalgal biofuel and bioproduct industry, where large scale production of algae is required. An understanding of the limits to cell growth and survival will ultimately affect approaches for the generation of biomass and increasing yields.