Construction of a High-Density Genetic Map and Identification of Leaf Trait-Related QTLs in Chinese Bayberry (Myrica rubra)

Chinese bayberry (Myrica rubra) is an economically important fruit tree that is grown in southern China. Owing to its over 10-year seedling period, the crossbreeding of bayberry is challenging. The characteristics of plant leaves are among the primary factors that control plant architecture and potential yields, making the analysis of leaf trait-related genetic factors crucial to the hybrid breeding of any plant. In the present study, molecular markers associated with leaf traits were identified via a whole-genome re-sequencing approach, and a genetic map was thereby constructed. In total, this effort yielded 902.11 Gb of raw data that led to the identification of 2,242,353 single nucleotide polymorphisms (SNPs) in 140 F1 individuals and parents (Myrica rubra cv. Biqizhong × Myrica rubra cv. 2012LXRM). The final genetic map ultimately incorporated 31,431 SNPs in eight linkage groups, spanning 1,351.85 cM. This map was then used to assemble and update previous scaffold genomic data at the chromosomal level. The genome size of M. rubra was thereby established to be 275.37 Mb, with 94.98% of sequences being assembled into eight pseudo-chromosomes. Additionally, 18 quantitative trait loci (QTLs) associated with nine leaf and growth-related traits were identified. Two QTL clusters were detected (the LG3 and LG5 clusters). Functional annotations further suggested two chlorophyll content-related candidate genes being identified in the LG5 cluster. Overall, this is the first study on the QTL mapping and identification of loci responsible for the regulation of leaf traits in M. rubra, offering an invaluable scientific for future marker-assisted selection breeding and candidate gene analyses

Table_1_Molecular cloning and functional analysis of Chinese bayberry MrSPL4 that enhances growth and flowering in transgenic tobacco.docx

Chinese bayberry (Myrica rubra) is an important tree in South China, with its fruit being of nutritional and high economic value. In this study, early ripening (ZJ), medium ripening (BQ) and late ripening (DK) varieties were used as test materials. Young leaves of ZJ, BQ and DK in the floral bud morphological differentiation periods were selected for transcriptome sequencing to excavate earliness related genes. A total of 4,538 differentially expressed genes were detected. Based on clustering analysis and comparisons with genes reportedly related to flowering in Arabidopsis thaliana, 25 homologous genes were identified. Of these, one gene named MrSPL4 was determined, with its expression down-regulated in DK but up-regulated in ZJ and BQ. MrSPL4 contained SBP domain and the target site of miR156, and its total and CDS length were 1,664 bp and 555 bp respectively. The overexpression vector of MrSPL4 (35S::35S::MrSPL4-pCambia2301-KY) was further constructed and successfully transfected into tobacco to obtain MrSPL4-positive plants. Based on the results of qRT-PCR, the relative expression of MrSPL4 was up regulated by 3,862.0-5,938.4 times. Additionally, the height of MrSPL4-positive plants was also significantly higher than that of wild-type (WT), with the bud stage occurring 12 days earlier. Altogether, this study identified an important gene -MrSPL4 in Chinese bayberry, which enhanced growth and flowering, which provided important theoretical basis for early-mature breeding of Chinese bayberry.</p