Codon use bias is an important characteristic in the process of genetic information transmission of species. With the publication of the genome of C. panzhihuaensis, it is of great significance to investigate the codon use bias for understanding the genetic evolution of this species and for molecular breeding. In this study, Perl language and CodonW 1.4.2 software was used to systematically analyze the coding gene sequences of the C. panzhihuaensis genome, obtain the characteristics of codon use, and identify the sources of variation affecting codon use. The results showed that GC3s content, GCall content, and ENC value were 46.75%, 47.67%, and 52.8 respectively. As the first seed plant, the GC3 content of Cycas is similar to that of most gymnosperms and most dicotyledons, but considerably different from that of monocotyledons.RSCU value was greater than 1, among which 21 codons ended in U or A. Enc-plot analysis, PR2-plot neutral plot analysis, and correlation coefficient analysis of Axis1 with GC3s and CAI revealed that the codon bias was mainly affected by natural selection, but also by mutation pressure and other factors. Thirty-one optimal codons of Cycas genes were screened. This research can provide a reference for the phylogeny and genome codon evolution of Cycas.

The recently identified Mulberry Mosaic Dwarf-associated Virus (MMDaV), associated with mosaic dwarf symptoms in Chinese mulberry leaves, is a newly discovered member of the Geminiviridae family. The MMDaV genome, a single or twin circular single-stranded DNA molecule measuring approximately 2.5-3.0 kb, encodes five proteins and two hypothetical proteins, including a coat protein (CP) and movement protein (MP). The co-evolutionary dynamics between viral and host codon usage significantly impact viral survival, fitness, immune evasion, and evolutionary pathways. This study applied bioinformatic analyses to examine the codon usage bias in thirty MMDaV genomes collected from mulberry leaves in four distinct Chinese provinces. We aimed to understand the drivers of preferred synonymous codon usage. The Effective Number of Codons (ENC) analysis revealed significant regional variations among MMDaV isolates, allowing their classification into two main categories: the southern China HNZX strain and the eastern China HDZX strain. The codon preference analysis displayed a viral preference for using A/U as the terminal base, indicating a bias towards A/U over G/C. Using a combination of position-specific base composition, ENC-Plot, RP2-Plot, Neutral plot, and correspondence analysis, we found that mutational pressure and natural selection substantially influence codon usage and drive MMDaV evolution. Our findings shed light on the complex interplay between MMDaV and its mulberry host and offer crucial insights into the virus's adaptive and evolutionary mechanisms.

In the NCBI database, as on June 6, 2020, total number of available complete genome sequences of SARS-CoV2 across the world is 3617. The envelope protein of SARS-CoV2 possesses several non-synonymous mutations over the transmembrane domain and (C)-terminus in 0.414\% of these 3617 genomes. The C-terminus motif DLLV has been changed to DFLV and YLLV in the proteins QJR88103 (Australia: Victoria) and QKI36831 (China: Guangzhou) respectively, which might affect the binding of this motif with the host protein PALS1.

Genus Clematis is one of the largest within Ranunculaceae. Here we report the chloroplast genome of two Clematis species, C. brachyura and C. trichotoma endemic to Korea. The chloroplast genome lengths of C. brachyura and C. trichotoma are 159,532 bp and 159,170 bp, respectively. Gene contents in the complete chloroplast genomes of these two Clematis species are identical to that of most Ranunculaceae and other angiosperms. However, our data results demonstrated that genus Clematis has inversion and rearrangement events concerning gene rps4 gene, rps16 to trnH region, and trnL to ndhC region, and IR regions expansion. Comparison of IR regions among Ranunculaceae species revealed that Clematis species contained six protein coding genes (infA, rps8, rpl14, rpl16, rps3, and rpl22) usually found in the long single copy (LSC) region of other species. Phylogenetic analysis demonstrated that genus Clematis is closely related to genus Ranunculus. Differences in repeat structure, substitution rates, and IR expansion in genera Clematis and Ranunculus, explained their relationship. Clematis species showed slightly higher tandem repeats content than Ranunculus species. The six protein-coding genes showed lower synonymous substitution rates in the IR of Clematis species than in the LSC of Ranunculus species. Overall, the chloroplast genomes and results presented here provide important information on the evolution of Ranunculaceae.

In December 2019, the novel severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) emerged in the province of Wuhan, China. Since then, it has spread worldwide with new mutations being reported. We performed genomic analysis to identify the changes in genetic diversity of SARS-CoV-2 between December 2019 and November 2020, and through molecular surveillance, we monitored the mutations that could be involved in viral fitness. We analyzed 2,213 complete genomes from 6 geographical regions worldwide, which were downloaded from GenBank and GISAID databases. Although SARS-CoV-2 presented low genetic diversity, there has been an increase over time, with the presence of several hotspot mutations throughout its genome. We identified 7 frequent mutations that resulted in non-synonymous substitutions (dN). Two of them, C14408T>P323L and A23403G>D614G, located in the nsp12 and Spike protein, respectively, emerged early in the pandemic and showed a considerable increase in frequency over time. Two other mutations, A1163T>I120F in nsp2 and G22992A>S477N in the Spike protein emerged recently and have spread in Oceania and Europe. Continuous molecular surveillance of SARS-CoV-2 will be necessary to detect and describe the transmission dynamics of new variants of the virus with clinical relevance. This information is important to improve programs to control the virus.

To understand SARS-CoV-2 microevolution, this study explored the genome-wide frequency, gene-wise distribution, and molecular nature of all point-mutations detected across its 71,703 RNA-genomes deposited in the GISAID repository, till 21 August 2020. Globally, nsp1/nsp2/nsp3/ nsp11 and orf7a/orf3a/S were the most mutation-ridden non-structural and structural genes respectively. Phylogeny based on 4,618 spatiotemporally-representative genomes revealed that entities belonging to the early lineages are mostly spread over Asian countries (including India, the biggest hotspot of the pandemic) whereas the recently-derived lineages are more globally distributed. Of the total 16,602 polymorphism-bearing sites in the pan-genome, 11,037 and 4,965 involved transitions and transversions, which in turn were predominated by cytidine-to-uridine and guanosine-to-uridine conversions, respectively. Positive selection of nonsynonymous mutations (dN/dS >1) in most of the structural, but not non-structural, genes indicated that SARS-CoV-2 has already harmonized its replication/transcription machineries with the host’s metabolic system, while it is still redefining virulence/transmissibility strategies at the molecular level.