Ming, R. | bioRxiv Science

bioRxiv2023

Allopolyploidization from two dioecious ancestors leads to recurrent evolution of sex chromosomes and reversion to autosomes

Polyploidization presents an unusual challenge for species with sex chromosomes, as it can lead to complex combinations of sex chromosomes that disrupt reproductive development. This is particularly true for allopolyploidization between species with different sex chromosome systems. Here we assemble haplotype-resolved chromosome-level genomes of a female allotetraploid weeping willow (Salix babylonica) and a male diploid Salix dunnii using Hi-C and PacBio HiFi reads. We use phylogenomics of nuclear and plastid genomes to show that weeping willow arose from crosses between female ancestor from the Salix clade, having XY sex chromosomes on chromosome 7, with a male ancestor from the Vetrix clade, having ancestral XY sex chromosomes on chromosome 15. Our analysis reveals that weeping willow has one pair sex chromosomes, ZW on chromosome 15, that derive from the ancestral XY sex chromosomes in the Vetrix-clade male ancestor, and the X chromosomes on chromosome 7 from the Salix-clade female ancestor has reverted to an autosome. Taken together, our results point to rapid evolution and reversion of sex chromosomes following allopolyploidization in weeping willow. Significance StatementWe assembled haplotype-resolved genomes and obtained gap-free sex chromosomes of a female allotetraploid weeping willow (Salix babylonica) and a male diploid Salix dunnii. The weeping willow arose from two dioecious ancestors, that have XY sex chromosomes on chromosome 7 and 15, respectively. The one pair sex chromosomes 15W and 15Z in weeping willow derived from ancestral 15X and 15Y, respectively. Inversions contributed to the evolutions of sex-linked regions (SLRs) of diploid and polyploid willows.

evolutionary biology↗

bioRxiv2018

Genomic footprints of repeated evolution of CAM photosynthesis in tillandsioid bromeliads

The adaptive radiation of Bromeliaceae (pineapple family) is one of the most diverse among Neotropical flowering plants. Diversification in this group was facilitated by several key innovations including the transition from C3 to CAM photosynthesis. We used a phylogenomic approach complemented by differential gene expression (RNA-seq) and targeted metabolite profiling to address the patterns and mechanisms of C3/CAM evolution in the extremely species-rich bromeliad genus Tillandsia and related taxa. Evolutionary analyses at a range of different levels (selection on protein-coding genes, gene duplication and loss, regulatory evolution) revealed three common themes driving the evolution of CAM: response to heat and drought, alterations to basic carbohydrate metabolism, and regulation of organic acid storage. At the level of genes and their products, CAM/C3 shifts were accompanied by gene expansion of a circadian regulator, re-programming of ABA-related gene expression, and adaptive sequence evolution of an enolase, effectively linking carbohydrate metabolism to ABA-mediated stress response. These changes include several pleiotropic regulators, which facilitated the evolution of correlated adaptive traits during a textbook adaptive radiation.

genomics↗