Convergent evolution is especially common in plants that have independently adapted to the same extreme environments (i.e., extremophile plants). The recent burst of omics data has alleviated many limitations that have hampered molecular convergence studies of non-model extremophile plants. In this review, we summarize cases of genomic convergence in these taxa to examine the extent and type of genomic convergence during the process of adaptation to extreme environments. Despite being well studied by candidate gene approaches, convergent evolution at individual sites is rare and often has a high false-positive rate when assessed in whole genomes. By contrast, genomic convergence at higher genetic levels has been detected during adaptation to the same extreme environments. Examples include the convergence of biological pathways and changes in gene expression, gene copy number, amino acid usage, and GC content. Higher convergence levels play important roles in the adaptive evolution of extremophiles and may be more frequent and involve more genes. In several cases, multiple types of convergence events have been found to co-occur. However, empirical and theoretical studies of this higher level convergent evolution are still limited. In conclusion, both the development of powerful approaches and the detection of convergence at various genetic levels are needed to further reveal the genetic mechanisms of plant adaptation to extreme environments.

No abstract

This study aims to investigate the value of chromosomal microarray analysis (CMA) and whole exome sequencing (WES) in fetuses with increased nuchal translucency (defined as NT above the 95th centile for the crown-rump length). A total of 374 singleton pregnancies with gestational ages ranging from 11 to 13 + 6 weeks were investigated. Ultrasound displayed increased NT and no detectable structural malformations in these fetuses. Pregnancies were divided into 4 groups according to the NT values: 95th centile-3.4 mm (114 cases); 3.5-4.4 mm (150 cases); 4.5-5.4 mm (55 cases); and ≥5.5 mm (55 cases). The possible chromosomal anomalies were all analyzed by CMA first. Furthermore, 24 cases with increased NT but negative CMA results were investigated by WES, and the outcomes were followed up. Among all the 374 cases, causative genetic defects were detected in 100/374 (26.7%) of the cases along with 9 variants of unknown significance (VOUS) by CMA. CMA testing yielded 30 pathogenic variants (30/55), accounting for a detection rate of 54.5%, and 1 VOUS in the group of NT ≥5.5 mm, indicating the highest detection rate in the 4 groups. The 24 cases of the CMA negative sub-cohort with WES analysis further yielded 2 VOUS and 3 likely pathogenic variants, including 2 dominant de novo mutations in SOS1 and ECE1 and 1 recessive inherited compound heterozygous mutation in PIGN, which are associated with cardiac defects. All 3 cases opted for termination of pregnancy (TOP). In addition, 2 cases with increased NT were negative by both CMA and WES analysis, and fetal demise occurred. In conclusion, for the investigation of fetuses with increased NT exome sequencing is suggested to be considered in cases with negative CMA findings. However, appropriate genetic counseling should be given to optimizing its utilization in prenatal diagnosis.

Objective To analyze the fetal fraction, fetal sex, and chromosomal aneuploidy in multiple pregnancies using noninvasive prenatal testing (NIPT). Method A total of 362 pregnant women including 203 singleton pregnancies, 69 twins, and 90 higher‐order multiple pregnancies were recruited. Fetal fractions estimated by size ratio‐based and Y chromosome‐based approaches in singleton pregnancies with male fetus were used as source data to establish the model. The model was then applied to multiple pregnancies for fetal fraction estimation. By comparing the fetal fractions estimated by size ratio to those estimated by Y chromosome or autosomal chromosomes, fetal sex and chromosomal aneuploidy can be analyzed. Results The size ratio‐based approach has been well established in estimating fetal fractions for twin and higher‐order multiple pregnancies. Fetal fraction had a positive correlation with gestational age in twin and triplet pregnancies. Fetal sex was determined with accuracies of 98.6% (95% CI, 92.19%‐99.96%) in twins and 97.6% (95% CI, 91.76%‐99.71%) in triplet pregnancies. Four trisomy 21, one trisomy 18, and one trisomy 13 cases were detected by NIPT. Two trisomy 21 singleton pregnancies and one trisomy 21 twin pregnancy were confirmed by karyotyping. Conclusion Fetal sex and chromosomal aneuploidy in multiple pregnancies can be determined using NIPT.