Sucrose is the principal transported product of photosynthesis from source leaves to sink organs. SUTs/SUCs (sucrose transporters or sucrose carriers) and SWEETs (Sugars Will Eventually be Exported Transporters) play significant central roles in phloem loading and unloading. SUTs/SUCs and SWEETs are key players in sucrose translocation and are associated with crop yields. The SUT/SUC and SWEET genes have been characterized in several plant species, but a comprehensive analysis of these two gene families in oilseed rape has not yet been reported. In our study, 22 and 68 members of the SUT/SUCs and SWEET gene families, respectively, were identified in the oilseed rape (Brassica napus) genome through homology searches. An analysis of the chromosomal distribution, phylogenetic relationships, gene structures, motifs and the cis-acting regulatory elements in the promoters of BnSUC and BnSWEET genes were analyzed. Furthermore, we examined the expression of the 18 BnSUC and 16 BnSWEET genes in different tissues of “ZS11” and the expression of 9 BnSUC and 7 BnSWEET genes in “ZS11” under various conditions, including biotic stress (Sclerotinia sclerotiorum), abiotic stresses (drought, salt and heat), and hormone treatments (abscisic acid, auxin, cytokinin, brassinolide, gibberellin, and salicylic acid). In conclusion, our study provides the first comprehensive analysis of the oilseed rape SUC and SWEET gene families. Information regarding the phylogenetic relationships, gene structure and expression profiles of the SUC and SWEET genes in the different tissues of oilseed rape helps to identify candidates with potential roles in specific developmental processes. Our study advances our understanding of the important roles of sucrose transport in oilseed rape.

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Yellow seed coat in rapeseed (Brassica napus) is a desirable trait that can be targeted to improve the quality of this oilseed crop. To better understand the inheritance mechanism of the yellow-seeded trait, we performed transcriptome profiling of developing seeds in yellow- and black-seeded rapeseed with different backgrounds. The differentially expressed genes (DEGs) during seed development showed significant characteristics, these genes were mainly enriched for the Gene Ontology (GO) terms carbohydrate metabolic process, lipid metabolic process, photosynthesis, and embryo development. Moreover, 1206 and 276 DEGs, which represent candidates to be involved in seed coat color, were identified between yellow- and black-seeded rapeseed during the middle and late stages of seed development, respectively. Based on gene annotation, GO enrichment analysis, and protein–protein interaction network analysis, the downregulated DEGs were primarily enriched for the phenylpropanoid and flavonoid biosynthesis pathways. Notably, 25 transcription factors (TFs) involved in regulating flavonoid biosynthesis pathway, including known (e.g., KNAT7, NAC2, TTG2 and STK) and predicted TFs (e.g., C2H2-like, bZIP44, SHP1, and GBF6), were identified using integrated gene regulatory network (iGRN) and weight gene co-expression networks analysis (WGCNA). These candidate TF genes had differential expression profiles between yellow- and black-seeded rapeseed, suggesting they might function in seed color formation by regulating genes in the flavonoid biosynthesis pathway. Thus, our results provide in-depth insights that facilitate the exploration of candidate gene function in seed development. In addition, our data lay the foundation for revealing the roles of genes involved in the yellow-seeded trait in rapeseed.

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The objective of this study was to identify QTLs for lignin content of seed coat in Brassica napus using the composite interval mapping (CIM) method. The recombinant inbred lines (RIL) population derived from a cross between black-seeded male parent cultivar Zhongyou 821 and yellow-seeded female parent line GH06 was established by selfing for seven successive generations with single seed propagating from F 2 . The population was grown at Beibei and Wanzhou in Chongqing in 2007. The QTLs of seed coat lignin content in two environments were detected using the genetic map constructed in 2007. A total of 12 QTLs for seed coat lignin content were located on the four linkage groups, each of them explained 4.50-8.79% of phenotypic variation. One QTL located on linkage group (LG) 3 was linked with the same marker EM19ME23/130 in two environments, other QTLs had different locations between two environments. The QTLs found in Beibei were mainly distributed on LG 20, and the QTLs detected in Wanzhou mainly distributed on LG 3. The QTLs for flavoid contents in embryo and seed color were located in the nearly region with some QTLs for seed coat lignin content. The correlation analysis showed the lignin content of seed coat had significantly and positively correlated with flavoid content of embryo in different environments. In conclution, (1) the seed coat lignin content is controlled by many minor-effect genes, with a genetic pattern of quantitative trait, and the expression of the QTL is affected by environmental factors greatly; (2) the syntheses of lignin in seed coat and flavoid of embryo are probably controlled by the same genes or have the same pathway partially.