The evolution of hemocyanin genes in Tectipleura: a multitude of conserved introns in highly diverse gastropods

Background Hemocyanin is the oxygen transporter of most molluscs. Since the oxygen affinity of hemocyanin is strongly temperature-dependent, this essential protein needs to be well-adapted to the environment. In Tectipleura, a very diverse group of gastropods with > 27,000 species living in all kinds of habitats, several hemocyanin genes have already been analyzed. Multiple independent duplications of this gene have been identified and may represent potential adaptations to different environments and lifestyles. The aim of this study is to further explore the evolution of these genes by analyzing their exon–intron architectures. Results We have reconstructed the gene architectures of ten hemocyanin genes from four Tectipleura species: Aplysia californica, Lymnaea stagnalis, Cornu aspersum and Helix pomatia. Their hemocyanin genes each contain 53 introns, significantly more than in the hemocyanin genes of Cephalopoda (9–11), Vetigastropoda (15) and Caenogastropoda (28–33). The gene structures of Tectipleura hemocyanins are identical in terms of intron number and location, with the exception of one out of two hemocyanin genes of L. stagnalis that comprises one additional intron. We found that gene structures that differ between molluscan lineages most probably evolved more recently through independent intron gains. Conclusions The strict conservation of the large number of introns in Tectipleura hemocyanin genes over 200 million years suggests the influence of a selective pressure on this gene structure. While we could not identify conserved sequence motifs within these introns, it may be simply the great number of introns that offers increased possibilities of gene regulation relative to hemocyanin genes with less introns and thus may have facilitated habitat shifts and speciation events. This hypothesis is supported by the relatively high number of introns within the hemocyanin genes of Pomacea canaliculata that has evolved independently of the Tectipleura. Pomacea canaliculata belongs to the Caenogastropoda, the sister group of Heterobranchia (that encompass Tectipleura) which is also very diverse and comprises species living in different habitats. Our findings provide a hint to some of the molecular mechanisms that may have supported the spectacular radiation of one of Metazoa’s most species rich groups.

Phosphate transporter genes: genome-wide identification and characterization in Camelina sativa

Phosphorus is known as a key element associated with growth, energy, and cell signaling. In plants, phosphate transporters (PHTs) are responsible for moving and distributing phosphorus in cells and organs. PHT genes have been genome-wide identified and characterized in various plant species, however, these genes have not been widely identified based on available genomic data in Camellia sativa, which is an important oil seed plant. In the present study, we found 66 PHT genes involved in phosphate transporter/translocate in C. sativa. The recognized genes belonged to PHTs1, PHTs2, PHTs4, PHOs1, PHO1 homologs, glycerol-3-PHTs, sodium dependent PHTs, inorganic PHTs, xylulose 5-PHTs, glucose-6-phosphate translocators, and phosphoenolpyruvate translocators. Our finding revealed that PHT proteins are divers based on their physicochemical properties such as Isoelectric point (pI), molecular weight, GRAVY value, and exon-intron number(s). Besides, the expression profile of PHT genes in C. sativa based on RNA-seq data indicate that PHTs are involved in response to abiotic stresses such as cold, drought, salt, and cadmium. The tissue specific expression high expression of PHO1 genes in root tissues of C. sativa. In additions, four PHTs, including a PHT4;5 gene, a sodium dependent PHT gene, and two PHO1 homolog 3 genes were found with an upregulation in response to aforementioned studied stresses. In the current study, we found that PHO1 proteins and their homologs have high potential to post-translation modifications such as N-glycosylation and phosphorylation. Besides, different cis-acting elements associated with response to stress and phytohormone were found in the promoter region of PHT genes. Overall, our results show that PHT genes play various functions in C. Sativa and regulate Camellia responses to external and intracellular stimuli. The results can be used in future studies related to the functional genomics of C. sativa.

Association of T2/S-RNase With Self-Incompatibility of Japanese Citrus Accessions Examined by Transcriptomic, Phylogenetic, and Genetic Approaches

Several citrus varieties show gametophytic self-incompatibility (GSI), which can contribute to seedless fruit production in several cultivars. This study investigated the genes regulating this trait through RNA-seq performed using styles collected from the flowers of Japanese citrus cultivars ‘Hyuganatsu,' ‘Tosabuntan,' ‘Hassaku,' ‘Banpeiyu,' and ‘Sweet Spring'. We screened the transcripts of putative T2 RNases, i.e., the protein family including all S-RNases from S-RNase-based GSI plants, and constructed a phylogenetic tree using the screened T2 RNases and S-RNases retrieved from citrus genome databases and a public database. Three major clusters (class I–III) were formed, among which, the class III cluster contained family specific subclusters formed by S-RNase and a citrus-specific cluster monophyletic to the S-RNase clusters. From the citrus class III cluster, six transcripts were consistent with the S haplotypes previously determined in Japanese citrus accessions, sharing characteristics such as isoelectric point, extracellular localization, molecular weight, intron number and position, and tissue-specific expression with S-RNases. One T2 RNase gene in self-incompatible Hyuganatsu was significantly down-regulated in the styles of a self-compatible mutant of Hyuganatsu in RNA-seq and qPCR analyses. In addition, the inheritance pattern of some T2 RNase genes was consistent with the pattern of the S haplotype in the progeny population of Hyuganatsu and Tosabuntan. As all results supported citrus self-incompatibility being based on S-RNase, we believe that six T2 RNase genes were S-RNases. The homology comparison between the six T2 RNases and S-RNases recently reported in Chinese citrus revealed that three out of six T2 RNases were identical to S-RNases from Chinese citrus. Thus, the other three T2 RNases were finally concluded to be novel citrus S-RNases involved in self-incompatibility.

Genome-wide identification and analysis of the thiolase family in insects

Thiolases are important enzymes involved in lipid metabolism in both prokaryotes and eukaryotes, and are essential for a range of metabolic pathways, while, little is known for this important family in insects. To shed light on the evolutionary models and functional diversities of the thiolase family, 137 thiolase genes were identified in 20 representative insect genomes. They were mainly classified into five classes, namely cytosolic thiolase (CT-thiolase), T1-thiolase, T2-thiolase, trifunctional enzyme thiolase (TFE-thiolase), and sterol carrier protein 2 thiolase (SCP2-thiolase). The intron number and exon/intron structures of the thiolase genes reserve large diversification. Subcellular localization prediction indicated that all the thiolase proteins were mitochondrial, cytosolic, or peroxisomal enzymes. Four highly conserved sequence fingerprints were found in the insect thiolase proteins, including CxS-, NEAF-, GHP-, and CxGGGxG-motifs. Homology modeling indicated that insect thiolases share similar 3D structures with mammals, fishes, and microorganisms. In Bombyx mori, microarray data and reverse transcription-polymerase chain reaction (RT-PCR) analysis suggested that some thiolases might be involved in steroid metabolism, juvenile hormone (JH), and sex pheromone biosynthesis pathways. In general, sequence and structural characteristics were relatively conserved among insects, bacteria and vertebrates, while different classes of thiolases might have differentiation in specific functions and physiological processes. These results will provide an important foundation for future functional validation of insect thiolases.

No Predictable Relationship Between Presacral Vertebral Number and Hes7 Intron Number Across Mammals

In mammals, the number of vertebrae and the somites they derive from is highly limited. Nevertheless, there are some lineages that have an increased number of presacral vertebrae and thus an elongated trunk. This suggests that somitogenesis, the process of somite formation in early development, is altered in these lineages. According the ‘clock and wavefront’ model of somitogenesis, temporal information of somite boundary formation is generated by a traveling wave of cyclic expression of oscillator genes. Hes7 has been suggested to be a key oscillator gene of this molecular segmentation clock. A previous study showed that reducing the number of introns within the Hes7 gene results in a more rapid tempo of Hes7 oscillation and an increased number of presacral vertebrae. Variation in Hes7 intron number could therefore be a potential evolutionary mechanism for varying vertebral number across mammals. In order to test this hypothesis, Hes7 intron number is here compared to presacral vertebral number across a variety of mammals.No significant relationship between both metrics could be detected as their variation across the mammalian phylogeny is fundamentally different. Integrating our data in the previously published mathematical model of Hes7 oscillation confirms the finding that variation in intron number does not predict variation in presacral vertebrae, rendering a direct causal relationship unlikely. However, our data support the previous suggestion that at least two introns are required for Hes7 pace making function of the segmentation clock.

Introns structure patterns of variation in nucleotide composition in Arabidopsis thaliana and rice protein-coding genes

Plant genomes are large, intron-rich and present a wide range of variation in coding region G+C content. Concerning coding regions, a sort of syndrome can be described in plants: the increase in G+C content is associated with both the increase in heterogeneity among genes within a genome and the increase in variation across genes. Taking advantage of the large number of genes composing plant genomes and the wide range of variation in gene intron number, we performed a comprehensive survey of the patterns of variation in G+C content at different scales from the nucleotide level to the genome scale in two species Arabidopsis thaliana and Oryza sativa, comparing the patterns in genes with different intron numbers. In both species, we observed a pervasive effect of gene intron number and location along genes on G+C content, codon and amino acid frequencies suggesting that in both species, introns have a barrier effect structuring G+C content along genes. In external gene regions (located upstream first or downstream last intron), species-specific factors are shaping G+C content while in internal gene regions (surrounded by introns), G+C content is constrained to remain within a range common to both species. In rice, introns appear as a major determinant of gene G+C content while in A. thaliana introns have a weaker but significant effect. The structuring effect of introns in both species is susceptible to explain the G+C content syndrome observed in plants.

Internal Regularity of D-Glyceraldehide-3-Phosphate Dehydrogenase Genes and Proteins

Internal Regularity ofD-Glyceraldehide-3-Phosphate Dehydrogenase Genes and ProteinsData of analysis of some GAPDH family gene exon and intron length (nt) and intron position coordinates as a sum of preceeding exon dimensions) and their internal regularity were analyzed based on a working hypothesis that primieval gene precursors were regular and periodic polynucleotides formed from oligonucleotides identical in size. The number of nucleotides in a gene repeat unit was denoted by a specific term - gene quantum and symbolQ. The following genes were analyzed: the chicken GAPDH (12 exons/11 introns) gene, theChlamidomonas reinhardtii gapA(6 exons, 5 introns) andgapC(7 exons, 6 introns) genes. The determined value ofQfor all these genes was identical and constituted 9 nucleotides. The sum total of all above-mentioned gene intron dimensions, independently of intron number in a gene, could be precisely quantized - expressed as a product of a gene quantum and a whole number, e.g., for the chicken GAPDH 1628 nt = 9 nt x 292,0. The garden peaPissum sativumfragment (amino acids 167-219) was partially regular (the repeat unit size 9 aa) and showed translational symmetry. The obtained data supported the model that the precursors of the modern genes were originated by nucleotide multiplication reactions.