Breeding response of transcript profiling in developing seeds of Brassica napus

Background: The upgrading of rapeseed cultivars has resulted in a substantial improvement in yield and quality in China over the past 30 years. With the selective pressure against fatty acid composition and oil content, high erucic acid-and low oil-content cultivars have been replaced by low erucic acid-and high oil-content cultivars. The high erucic acid cultivar Zhongyou 821 and its descendent, low erucic acid cultivar Zhongshuang 9, are representatives of two generations of the most outstanding Chinese rapeseed cultivars (B. napus) developed the past 2 decades. This paper compares the transcriptional profiles of Zhongshuang 9 and Zhongyou 821 for 32 genes that are principally involved in lipid biosynthesis during seed development in order to elucidate how the transcriptional profiles of these genes responded to quality improvement over the past 20 years. Results: Comparison of the cultivar Zhongyou 821 with its descendent, Zhongshuang 9, shows that the transcriptional levels of seven of the 32 genes were upregulated by 30% to 109%, including FAD3, ACCase, FAE1, GKTP, Caleosin, GAPDH, and PEPC. Of the 32 genes, 10 (KAS3, beta-CT, BcRK6, P450, FatA, Oleosin, FAD6, FatB, alpha-CT and SUC1) were downregulated by at least 20% and most by 50%. The Napin gene alone accounted for over 75% of total transcription from all 32 genes assessed in both cultivars. Most of the genes showed significant correlation with fatty acid accumulation, but the correlation in ZS9 was significantly different from that in ZY821. Higher KCR2 activity is associated with higher C16:0, C18:0, and C18:2 in both cultivars, lower C22:1 and total fatty acid content in ZY821, and lower 18:1 in ZS9. Conclusion: This paper illustrates the response of the transcription levels of 32 genes to breeding in developing rapeseed seeds. Both cultivars showed similar transcription profiles, with the Napin gene predominantly transcribed. Selective pressure for zero erucic acid, low glucosinolate, high oleic acid and high oil content, as well as high yield, resulted in higher FAD3, ACCase, FAE1, GKTP, Caleosin, GAPDH, and PEPC expression levels and lower KAS3, beta-CT, BcRK6, P450, FatA, Oleosin, FAD6, FatB, alpha-CT and SUC1 expression levels. It also resulted in altered relationships between these genes during storage accumulation in seed development.