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The B-box proteins are a class of zinc finger transcription factors and play important roles in regulating plant growth, development, and stress response. However, their origin and expansion model in plants have been very vague. In this study, 208 B-box genes were identified in 18 plant species, and phylogenetic analyses divided them into five structure groups. Subsequently, the sequence analysis including theoretical isoelectric point, instability index, and aliphatic index showed the wide variation of B-box gene in different species. Our multispecies genome-wide analysis reveals that the structure groups III and IV in the plant BBX gene family have the earliest origin (Rhodophyta) and are extensively expanded in land plants, while the other three structure groups (I, II, and V) seem to originate at least in the last common ancestor of land plants. Furthermore, whole genome duplication (WGD) was the main driver (28 gene pairs, 65.12%) of the B-box gene family expansion, followed by segmental duplication, which tend to have more introns and are subject to more intense purification selections. We also analyzed the sequence differences between B-box domains to propose a new evolutionary model of B-box domain. These analyses provide new insights for understanding the origin and evolution of the B-box gene family. [ABSTRACT FROM AUTHOR]

Sea buckthorn is a typical drought-resistant tree species. However, there is a general lack of understanding of the pattern of DNA methylation linked with sea buckthorn responses to drought, and its relationship with drought tolerance mechanisms. In this study, we performed whole-transcriptome RNA sequencing and methylome sequencing in response to drought stress to explore differentially expressed mRNAs, miRNAs, lncRNAs and circRNAs in sea buckthorn leaves. Based on predicted DE pairs, we constructed a competitive endogenous RNA network, which revealed potential transcriptional regulatory roles in response to drought stress. The results of methylome sequencing revealed that the DNA methylation level was increased in sea buckthorn leaves under drought stress. We identified 13,405 differentially methylated regions between CK and TR. We found one DMR-associated DEG (Vacuolar-sorting receptor 6) involved in the ABA accumulation pathway. In addition, two DNA methyltransferases (HrMET1 and HrDRM1) were closely associated with drought-induced hypermethylation in sea buckthorn. Together, we firstly conducted a comprehensive transcriptomic and epigenetic analysis of sea buckthorn under drought stress, providing a resource for further study of the potential functions of genes, miRNAs, lncRNAs, circRNAs and DNA methyltransferases. • Transcriptome and methylome of sea buckthorn leaves were generated. • Drought stress can increase DNA methylation level of sea buckthorn leaves. • Vacuolar-sorting receptor 6 were involved in the ABA accumulation pathway. • HrMET1 and HrDRM1 were associated with drought-induced hypermethylation. [ABSTRACT FROM AUTHOR]

Key message: Genome-wide identification of the sea buckthorn GRAS genes and their transcription profiles in different organizations. GRAS proteins comprise a large family of transcription factors that experienced extensive replication, and play important roles in many aspects of growth regulatory and environmental signals. Sea buckthorn is a unique and valuable plant which has tremendous value for medical researching, ecological protection, and providing daily necessities. We identified, characterized, and distinguished duplication models of GRAS transcription factors in sea buckthorn. A systematic whole-genome analysis was performed to identify and characterize the GRAS gene family of sea buckthorn, especially the comparative genome method was used to demonstrate its different duplication models. We identified 62 sea buckthorn GRAS (HrGRAS) genes and renamed based on their respective chromosome distribution. Fifty-nine HrGRASs were classified into nine subgroups and three HrGRASs did not belong to any of the subfamilies according to their phylogenetic features. HrGRAS genes tend to have a representative GRAS domain, few introns, and unevenly distributed on chromosomes. Segmental duplication was the main driver of the GRAS gene family expansion, followed by whole-genome duplication (WGD) and tandem duplication, according to the results of comparative genome analysis. GRAS genes involved in duplication experienced strong purifying selection pressure according to the Ka/Ks ratios. The expression profile derived from transcriptome data shows the expression patterns of HrGRAS gene in different tissues and the characterization of differentially expressed genes. This systematic analysis provided a foundation to understand the expansion and potential functions of GRAS genes with an aim of sea buckthorn crop improvement. [ABSTRACT FROM AUTHOR]