A key molecular signature of biological aging is the accumulation of somatic mutations in the genome. Typically, somatic mutations are repaired by pathways whose efficiency decreases with age. However, recent studies of long-lived tree species indicate that the rate of somatic mutation accumulation is far lower than rates in shorter-lived species. Furthermore, somatic mutation accumulation may even be considered advantageous in long-lived plants, potentially providing offspring with additional genetic variation upon which natural selection can act. This raises questions: (i) do all long-lived plant species show reduced somatic mutation accumulation? (ii) how do they overcome these mutations? And (iii) what potential benefit do these mutations impart?
Welwitschia mirabilis is a remarkable plant endemic to the Namib Desert. It has been suggested that Welwitschia individuals may live as long as 2000 years. Given there is considerable interest in how long-lived plants achieve their longevity, studying this plant at the molecular level could provide valuable insight into the ways such a unique plant has managed to elude the aging process and to adapt to life in an extreme desert environment. Previous studies examining the accumulation of somatic mutations in long-lived species have been conducted in tall, branching trees. It is unclear whether such patterns would be seen in the uniquely structured Welwitschia plants, given that they have no branches and simply grow larger in circumference with age. We aim to answer some of the questions raised above using genomic data from several differently sized Welwitschia individuals sampled from natural populations in Namibia.