The black‐spotted pond frog Pelophylax nigromaculatus is a typical temperate‐adapted amphibian species, largely endemic to East Asia. It occurs from central, east, and northeast China, to the Russian Far East, the Korean Peninsula, and part of Japan. So far, little is known about this frog from the Loess Plateau, a region that has experienced profound changes in climate and environment since the late Miocene. Particularly, between the Loess Plateau and the North China Plain, stand the Lüliang and Taihang mountain ranges, which form an important geographical divide in East China. Therefore, frogs from the Loess Plateau are indispensable for understanding the biogeography and evolution of this species. In this study, a total of 933 specimens of P. nigromaculatus collected range‐wide were sequenced for the mitochondrial Cyt b gene, with 345 of them being genotyped at 10 nuclear microsatellite loci. Both mitochondrial and microsatellite data resolved four major frog clades: (i) Loess Plateau clade, containing only frogs from the Loess Plateau; (ii) East China clade, containing frogs from the rest of China except those from the Liaodong Peninsula; (iii) Peninsulas clade, comprising frogs from the Korean Peninsula and Liaodong Peninsula; and (iv) Japan clade. Frogs from the Loess Plateau have deeply diverged from frogs in the remaining regions, with 11.5%–13.1% sequence divergence, which is comparable to distances between congeneric ranid species. Ecological niche modeling analysis showed that the potential distribution ranges of the Loess Plateau frogs and the non‐Loess Plateau frogs are rather different; niche identity testing indicated that the environmental niches of frogs from the Loess Plateau and other regions are not equivalent. Our data thus suggest that the Loess Plateau frogs represent a cryptic species. The uplift of the Lüliang Mountains was the most plausible trigger of this cryptic diversification.

Reference-quality genomes of both sexes are essential for studying sex determination and sex-chromosome evolution, as their gene contents and expression profiles differ. Here, we present independent chromosome-level genome assemblies for the female (XX) and male (XY) genomes of desert poplar (Populus euphratica), resolving a 22.7-Mb X and 24.8-Mb Y chromosome. We also identified a relatively complete 761-kb sex-linked region (SLR) in the peritelomeric region on chromosome 14 (Y). Within the SLR, recombination around the partial repeats for the feminizing factor ARR17 (ARABIDOPSIS RESPONSE REGULATOR 17) was potentially suppressed by flanking palindromic arms and the dense accumulation of retrotransposons. The inverted small segments S1 and S2 of ARR17 exhibited relaxed selective pressure and triggered sex determination by generating 24-nt small interfering RNAs that induce male-specific hyper-methylation at the promoter of the autosomal targeted ARR17. We also detected two male-specific fusion genes encoding proteins with NB-ARC domains at the breakpoint region of an inversion in the SLR that may be responsible for the observed sexual dimorphism in immune responses. Our results show that the SLR appears to follow proposed evolutionary dynamics for sex chromosomes and advance our understanding of sex determination and the evolution of sex chromosomes in Populus.

Background Maize is an important model organism for genetics and genomics research. Though reference genomes of maize are available, some genomes of important genetic germplasms for maize breeding are still lacking, for instance, the cultivar Dan340, which is a backbone inbred line of the LvDa Red Cob Group with several desirable characteristics. In this study, we constructed a high-quality chromosome-level reference genome for Dan340 by using long HiFi reads, short reads, and Hi-C. The final assembly of the Dan340 genome was 2348.72 Mb, which was anchored to 10 chromosomes. Repeat sequences accounted for 73.40% of the genome and 39,733 protein-coding genes were annotated. Comparative genomic analysis between Dan340 and other maize lines identified that 1806 genes from 359 gene families were specific to Dan340. Conclusions Our genome assembly and annotation provide a valuable resource for improving maize breeding and further understanding the intraspecific genome diversity in maize.

The maize cultivar Dan340 is an excellent backbone inbred line of Luda Red Cob Group with several desirable characters, such as disease resistance, lodging resistance, high combining ability, wide adaptability and so on. In this study, we constructed a high-quality chromosome-level reference genome for Dan340 by combining PacBio long HiFi sequencing, Illumina short reads and chromosomal conformational capture (Hi-C) sequencing reads. The final assembly of Dan340 genome was 2,348.72 Mb, including 2,738 contigs and 2,315 scaffolds with a N50 of 41.49 Mb and 215.35 Mb, respectively. The percent of high quality Illumina reads mapped to the reference genome was up to 97.48%. The assembly of this genome will not only facilitate our understanding about intraspecific genome diversity in maize, but also provides a novel resource for maize breeding.