Functional Differentiation of the Duplicated Gene BrrCIPK9 in Turnip (Brassica rapa var. rapa).

Gene duplication is a key biological process in the evolutionary history of plants and an important driving force for the diversification of genomic and genetic systems. Interactions between the calcium sensor calcineurin B-like protein (CBL) and its target, CBL-interacting protein kinase (CIPK), play important roles in the plant's response to various environmental stresses. As a food crop with important economic and research value, turnip (Brassica rapa var. rapa) has been well adapted to the environment of the Tibetan Plateau and become a traditional crop in the region. The BrrCIPK9 gene in turnip has not been characterized. In this study, two duplicated genes, BrrCIPK9.1 and BrrCIPK9.2, were screened from the turnip genome. Based on the phylogenetic analysis, BrrCIPK9.1 and BrrCIPK9.2 were found located in different sub-branches on the phylogenetic tree. Real-time fluorescence quantitative PCR analyses revealed their differential expression levels between the leaves and roots and in response to various stress treatments. The differences in their interactions with BrrCBLs were also revealed by yeast two-hybrid analyses. The results indicate that BrrCIPK9.1 and BrrCIPK9.2 have undergone Asparagine-alanine-phenylalanine (NAF) site divergence during turnip evolution, which has resulted in functional differences between them. Furthermore, BrrCIPK9.1 responded to high-pH (pH 8.5) stress, while BrrCIPK9.2 retained its ancestral function (low K+), thus providing further evidence of their functional divergence. These functional divergence genes facilitate turnip's good adaptation to the extreme environment of the Tibetan Plateau. In summary, the results of this study reveal the characteristics of the duplicated BrrCIPK9 genes and provide a basis for further functional studies of BrrCBLs-BrrCIPKs in turnip.

Chromosome-level genome assembly of Murraya paniculata sheds light on biosynthesis of floral volatiles.

BACKGROUND: Murraya paniculata (L.) Jack, commonly called orange jessamine in the family Rutaceae, is an important ornamental plant in tropical and subtropical regions which is famous for its strong fragrance. Although genome assemblies have been reported for many Rutaceae species, mainly in the genus Citrus, full genomic information has not been reported for M. paniculata, which is a prerequisite for in-depth genetic studies on Murraya and manipulation using genetic engineering techniques. Here, we report a high-quality chromosome-level genome assembly of M. paniculata and aim to provide insights on the molecular mechanisms of flower volatile biosynthesis. RESULTS: The genome assembly with a contig N50 of 18.25 Mb consists of 9 pseudomolecules and has a total length of 216.86 Mb. Phylogenetic analysis revealed that M. paniculata diverged from the common ancestor approximately 25 million years ago and has not undergone any species-specific whole genome duplication events. Genome structural annotation and comparative genomics analysis revealed that there are obvious differences in transposon contents among the genomes of M. paniculata and Citrus species, especially in the upstream regions of genes. Research on the flower volatiles of M. paniculata and C. maxima at three flowering stages revealed significant differences in volatile composition with the flowers of C. maxima lacking benzaldehyde and phenylacetaldehyde. Notably, there are transposons inserted in the upstream region of the phenylacetaldehyde synthase (PAAS) genes Cg1g029630 and Cg1g029640 in C. maxima, but not in the upstream region of three PAAS genes Me2G_2379, Me2G_2381, and Me2G_2382 in M. paniculata. Our results indicated that compared to the low expression levels of PAAS genes in C. maxima, the higher expression levels of the three PAAS genes in M. paniculata are the main factor affecting the phenylacetaldehyde biosynthesis and causing the content difference of phenylacetaldehyde. The phenylacetaldehyde synthetic activities of the enzymes encoded by M. paniculata PAAS genes were validated by in vitro analyses. CONCLUSIONS: Our study provides useful genomic resources of M. paniculata for further research on Rutaceae plants, identifies new PAAS genes, and provides insights into how transposons contribute to variations in flower volatiles among Murraya and Citrus plants.