On the ecology and evolution of fungal senescence

Aging evolves in the shadow of natural selection: Since the efficiency of natural selection declines with age, organisms will over the course of generations accumulate intrinsic, genetic factors that have a negative effect only late in life. This is generally known as the 'mutation accumulation' theory of aging. Should these factors additionally have apleiotropic, positive effect early on in life, for example on fertility, they could even befavoredby natural selection. This is known as the 'antagonisticpleiotropy' theory of aging. Aging is thus expected to be a multi-causal process resulting from intrinsic factors with negative effects late in life and possibly additional, positive effects early in life. It can be seen as the result of a lack of investment in somatic maintenance, a legacy of an organism's evolutionary past.In contrast to unitary organisms like most animals, modular organisms like plants, fungi and colonial invertebrates should not be subject to aging: In these organisms, there is no clear distinction between germ line and soma. Because the germ line should be immortal, in modular organisms aging or senescence is generally not expected, though parts or modules may be subject to aging or senescence. Though this is rare, there are striking examples oforganismalsenescence in fungi and plants, in which all parts of an individual die at the same time.This thesis deals with aging in two genera of filamentous fungi:NeurosporaandPodospora. It deals with the question whether there are similarities, both at the proximate or mechanistic level and at the ultimate or evolutionary level, between aging processes in fungi and aging processes as we know them from animals. It is shown that, at least in the pseudo-homothallic filamentousascomycetePodosporaanserina, aging is an intrinsic andmulticausalprocess as may be expected. An analysis of natural variation in life span shows that the main source of variation in life span corresponds to the presence or absence of mitochondrial plasmids, molecular parasites that interfere with respiration. Variation that arises spontaneously in the laboratory often corresponds to mitochondrial mutations in the electron transport chain. The latter mutations are all associated with the induction of alternative; nuclear encoded respiratory pathways and this leads via a yet unknown route to a stabilization of the otherwise unstable mitochondrial genome, a reduced level of reactive oxygen species as well as a reduced energy level. These mutations hence confer longevity at the cost of fertility. In addition to spontaneous mutations and chemical modifications of the electron transport chain, a dietary  reduction in the amount of glucose can extend life span in fungi. The latter effect is strongly reduced by the presence of a type of mitochondrial plasmid that interferes with respiration, which indicates that it is strongly dependent on properly functioning mitochondria. The latter underlines the critical role of mitochondria in the fungal senescence

Bibliographic Details

Main Author:	Maas, M.F.P.M.
Other Authors:	Hoekstra, Rolf
Format:	Doctoral thesis biblioteca
Language:	English
Subjects:	aging, cellular biology, ecology, evolution, genetics, mitochondria, mutations, neurospora, pezizomycotina, plasmids, senescence, celbiologie, ecologie, evolutie, genetica, mutaties, plasmiden, verouderen, veroudering,
Online Access:	https://research.wur.nl/en/publications/on-the-ecology-and-evolution-of-fungal-senescence
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