Dates and rates in grape's plastomes: evolution in slow motion

The family Vitaceae includes the domesticated grapevine (Vitis vinifera), one of the most economically important crops in the world. Despite the importance of Vitaceae, there is still considerable controversy surrounding their phylogenetic relationships and evolutionary timescales. Moreover, variation in rates of molecular evolution among Vitaceae remains mostly unexplored. The present research aims to fill these knowledge gaps through the analysis of plastome sequences. Thirteen newly sequenced grape plastomes are presented and their phylogenetic relationships examined. Divergence times and absolute substitution rates are inferred under different molecular clocks by the analysis of 95 non-coding plastid regions and 43 representative accessions of the major lineages of Vitaceae. Furthermore, the phylogenetic informativeness of non-coding plastid regions is investigated. We find strong evidence in favor of the random local clock model and rate heterogeneity within Vitaceae. Substitution rates decelerate in Ampelocissus, Ampelopsis, Nekemias, Parthenocissus, Rhoicissus, and Vitis, with genus Vitis showing the lowest values up to a minimum of ~ 4.65 × 10^-11 s/s/y. We suggest that liana-like species of Vitaceae evolve slower than erect growth habit plants and we invoke the "rate of mitosis hypothesis" to explain the observed pattern of the substitution rates. We identify a reduced set of 20 non-coding regions able to accurately reconstruct the phylogeny of Vitaceae and we provide a detailed description of all 152 non-coding regions identified in the plastomes of subg. Vitis. These polymorphic regions will find their applications in phylogenetics, phylogeography, and population genetics as well in grapes identification through DNA barcoding techniques.