Genetic Contribution of Paleopolyploidy to Adaptive Evolution in Angiosperms

Ancient whole-genome duplications (WGDs or polyploidy) are prevalent in plants, and some WGDs occurred during the timing of severe global environmental changes. It has been suggested that WGDs may have contributed to plant adaptation. However, this still lacks empirical evidence at the genetic level to support the hypothesis. Here, we investigated the survivors of gene duplicates from multiple ancient WGD events on the major branches of angiosperm phylogeny, and aimed to explore genetic evidence supporting the significance of polyploidy. Duplicated genes co-retained from three waves of independent WGDs (similar to 120 million years ago [Ma], similar to 66, and <20 Ma) were investigated in 25 selected species. Gene families functioning in low temperature and darkness were commonly retained gene duplicates after the eight independently occurring WGDs in many lineages around the Cretaceous-Paleocene boundary, when the global cooling and darkness were the two main stresses. Moreover, the commonly retained duplicates could be key factors which may have contributed to the robustness of the critical stress-related pathways. In addition, genome-wide transcription factors (TFs) functioning in stresses tend to retain duplicates after waves of WGDs, and the coselected gene duplicates in many lineages may play critical roles during severe environmental stresses. Collectively, these results shed new light on the significant contribution of paleopolyploidy to plant adaptation during global environmental changes in the evolutionary history of angiosperms

The Chromosome-Level Genome of <i>Elaeagnus moorcroftii</i> Wall., an Economically and Ecologically Important Tree Species in Drylands

Elaeagnus moorcroftii Wall. (Elaeagnaceae) is an important tree species naturally growing in arid Northwest China that has great economic and ecological values in drylands. In this study, we de novo assembled a chromosome-level genome for E. moorcroftii by using PacBio’s high-fidelity (HiFi) sequencing and Hi-C-assisted assembly technology. The assembled genome size was 529.56 Mb, of which 94.56% was anchored to 14 pseudochromosomes with a contig N50 up to 28.21 Mb. In total, 29,243 protein-coding genes were annotated, and 98.5% of the Benchmarking Universal Single-Copy Orthologs (BUSCOs) were captured in the genome. Evolutionary genomic analysis showed that E. moorcroftii split with Elaeagnus mollis 9.38 million years ago (Ma), and contrasted evolutionary trajectories of gene family expansion and contraction were observed for these two closely related species. Furthermore, we identified two successive whole genome duplication (WGD) events occurred in the genome of E. moorcroftii, in addition to the ancient gamma hexaploidization event shared by core eudicots. Together, the chromosome-level genome assembly for E. moorcroftii decoded here provides valuable genomic information for the further genetic improvement and molecular breeding of this indigenous species in drylands

The complete chloroplast genome sequence of Opuntia sulphurea (Cactaceae)

Opuntia sulphurea Gillies ex Salm-Dyck 1834 (Cactaceae) acts as an invasive species due to its ability to survive in various environments. In this study, we assembled the complete chloroplast (cp) genome of Opuntia sulphurea, which was 122,740 bp in length. The genome contained 100 genes, including 65 protein-coding genes, 31 tRNA genes and four rRNA genes. The base composition of the chloroplast genome was 32.11% A, 17.74% G, 18.34% C, and 31.80% T, resulting in an overall G + C content of 35.39%. A phylogenetic analysis across 23 species in Caryophyllales demonstrated a close relationship between Opuntia sulphurea and Opuntia quimilo

The Chromosome-Level Genome of Elaeagnus moorcroftii Wall., an Economically and Ecologically Important Tree Species in Drylands

Elaeagnus moorcroftii Wall. (Elaeagnaceae) is an important tree species naturally growing in arid Northwest China that has great economic and ecological values in drylands. In this study, we de novo assembled a chromosome-level genome for E. moorcroftii by using PacBio&rsquo;s high-fidelity (HiFi) sequencing and Hi-C-assisted assembly technology. The assembled genome size was 529.56 Mb, of which 94.56% was anchored to 14 pseudochromosomes with a contig N50 up to 28.21 Mb. In total, 29,243 protein-coding genes were annotated, and 98.5% of the Benchmarking Universal Single-Copy Orthologs (BUSCOs) were captured in the genome. Evolutionary genomic analysis showed that E. moorcroftii split with Elaeagnus mollis 9.38 million years ago (Ma), and contrasted evolutionary trajectories of gene family expansion and contraction were observed for these two closely related species. Furthermore, we identified two successive whole genome duplication (WGD) events occurred in the genome of E. moorcroftii, in addition to the ancient gamma hexaploidization event shared by core eudicots. Together, the chromosome-level genome assembly for E. moorcroftii decoded here provides valuable genomic information for the further genetic improvement and molecular breeding of this indigenous species in drylands

The ancient wave of polyploidization events in flowering plants and their facilitated adaptation to environmental stress

Flowering plants, or angiosperms, consist of more than 300,000 species, far more than any other land plant lineages. The accumulated evidence indicates that multiple ancient polyploidy events occurred around 100 to 120 million years ago during the Cretaceous and drove the early diversification of four major clades of angiosperms:gammawhole-genome triplication in the common ancestor of core eudicots,tauwhole-genome duplication during the early diversification of monocots,lambdawhole-genome duplication during the early diversification of magnoliids, andpiwhole-genome duplication in the Nymphaeales lineage. These four polyploidy events have played essential roles in the adaptive evolution and diversification of major clades of flowering plants. Here, we specifically review the current understanding of this wave of ancient whole-genome duplications and their evolutionary significance. Notably, although these ancient whole-genome duplications occurred independently, they have contributed to the expansion of many stress-related genes (e.g., heat shock transcription factors and Arabidopsis response regulators)?and these genes could have been selected for by global environmental changes in the Cretaceous. Therefore, this ancient wave of paleopolyploidy events could have significantly contributed to the adaptation of angiosperms to environmental changes, and potentially promoted the wide diversification of flowering plants

Niche conservatism and elevated diversification shape species diversity in drylands: evidence from Zygophyllaceae

The integrated contributions of climate and macroevolutionary processes to global patterns of species diversity are still controversial in spite of a long history of studies. The niche conservatism hypothesis and the net diversification rate hypothesis have gained wide attention in recent literature. Many studies have tested these two hypotheses for woody species in humid forests; however, the determinants of species diversity patterns for arid-adapted plants remain largely ignored. Here, using a molecular phylogeny and the global distributions of Zygophyllaceae, a typical arid-adapted plant family, we assessed the effects of contemporary climate and net diversification rates on species diversity patterns in drylands. We found the variables representing water availability to be the best predictors for Zygophyllaceae diversity. Specifically, Zygophyllaceae species diversity significantly decreased with the increase in water availability, probably owing to phylogenetic conservatism of water-related niches. The net diversification rates of Zygophyllaceae accelerated sharply in the recent 10 Myr, coinciding roughly with the period of global aridification. The species diversity of Zygophyllaceae significantly increased with the increase in mean net diversification rates per geographical unit, especially in the OldWorld, supporting the net diversification rate hypothesis. Our study provides a case exploring climatic and evolutionary mechanisms of dryland species diversity patterns, and suggests that the conservatism in water-related niches and elevated net diversification rates in drylands may have jointly determined the global patterns of dryland species diversity