Expression patterns of Brassica napus genes implicate IPT sucrose transporter, cell wall invertase, and amino acid permease gene family members in leaf, flower, silique, and seed development

Forage brassica (Brassica napus cv. Greenland) is bred for vegetative growth and biomass production, while its seed yield remains to be improved for seed producers without affecting forage yield and quality. Cytokinins affect seed yield by influencing flower, silique and seed number, and seed size. To identify specific cytokinin gene family members as targets for breeding, as well as genes associated with yield and/or quality, a B. napus transcriptome was obtained from a mixed sample including leaves, flower buds and siliques of various stages. Gene families for cytokinin biosynthesis (BnIPT1, 2, 3, 5, 7, 8 and 9), cytokinin degradation (BnC 1 to BnCKX7), cell wall invertase (BnCWINV1 to BnCWINV6), sugar transporter (BnSUT1 to BnSUT6) and amino acid permease (BnAAP1 to BnAAP8) were identified. As B. napus is tetraploid, homoeologues of each gene family member were sought. Using multiple alignments and phylogenetic analysis, the parental genomes of the two B. napus homoeologues could be differentiated. RT-qPCR was then used to determine the expression of gene family members and their homoeologues in leaves, flowers, siliques and seeds of different developmental stages. The expression analysis showed both temporal and organ-specific expression profiles among members of these multi-gene families. Several pairs of homoeologues showed differential expression, both in terms of level of expression and differences in temporal or organ-specificity. BnCKX2 and 4 were identified as targets for TILLING, EcoTILLING and MAS.