The kalilo Senescence Factor of Neurospora Intermedia: A Mitochondrial is-Element Derived from a Nuclear Plasmid

Abstract

The wild isolates of Neurospora intermedia from the Hawaiian island of Kauai consist of two classes: (a) “normal” strains that can be propagated virtually indefinitely by serial transfers of asexual spores (conidia), and (b) kalilo strains that go through a process of clonal deterioration and die after a very limited number of transfers, usually fewer than twenty (6). The process leading to vegetative death in kalilo strains has been defined as “senescence.” Senescence is characterized by the appearance of an abnormal stop-start growth phenotype in the mycelium (10) and by a progressive deterioration in mitochondrial functions, including a gradual disappearance of cytochromes aa ₃ and b and an accumulation of rearranged mitochondrial chromosomes (mtDNA) (2). The rearrangements in the mtDNAs of senescing kalilo cultures consist primarily of large insertions, deletions, and inversions (2).