The genomic diversification of clonally propagated grapevines

Abstract

Vegetatively propagated clones accumulate somatic mutations. The purpose of this study was to better understand the consequences of clonal propagation and involved defining the nature of somatic mutations throughout the genome. Fifteen Zinfandel winegrape clone genomes were sequenced and compared to one another using a highly contiguous genome reference produced from one of the clones, Zinfandel 03.\n\nThough most heterozygous variants were shared, somatic mutations accumulated in individual and subsets of clones. Overall, heterozygous mutations were most frequent in intergenic space and more frequent in introns than exons. A significantly larger percentage of CpG, CHG, and CHH sites in repetitive intergenic space experienced transition mutations than genic and non-repetitive intergenic spaces, likely because of higher levels of methylation in the region and the increased likelihood of methylated cytosines to spontaneously deaminate. Of the minority of mutations that occurred in exons, larger proportions of these were putatively deleterious when they occurred in relatively few clones.\n\nThese data support three major conclusions. First, repetitive intergenic space is a major driver of clone genome diversification. Second, clonal propagation is associated with the accumulation of putatively deleterious mutations. Third, the data suggest selection against deleterious variants in coding regions such that mutations are less frequent in coding than noncoding regions of the genome.