Triacylglycerol (TAG) is the major carbon storage reserve in oilseeds such as Arabidopsis. Acyl-CoA:diacylglycerol acyltransferase (DGAT) catalyses the final step of the TAG synthesis pathway. Although TAG is mainly accumulated during seed development, and DGAT has presumably the highest activity in developing seeds, we show here that TAG synthesis is also actively taking place during germination and seedling development in Arabidopsis. The expression pattern of the DGAT1 gene was studied in transgenic plants containing the reporter gene beta-glucuronidase (GUS) fused with DNA sequences flanking the DGAT1 coding region. GUS activity was not only detected in developing seeds and pollen, which normally accumulate storage TAG, but also in germinating seeds and seedlings. Western blots showed that DGAT1 protein is present in several tissues, though is most abundant in developing seeds. In seedlings, DGAT1 is expressed in shoot and root apical regions, correlating with rapid cell division and growth. The expression of GUS in seedlings was consistent with the results of RNA gel blot analyses, precursor feeding and DGAT assay. In addition, DGAT1 gene expression is up-regulated by glucose and associated with glucose-induced changes in seedling development.

Seed loss caused by pod-shatter during harvesting is one of the main problems in rapeseed production worldwide. Quantitative trait loci (QTLs) for pod-shatter based on genetic mapping would help breeders develop cultivars resistant to pod-shatter. In this study, we constructed a genetic map of Brassica napus containing 107 simple sequence repeat (SSR) markers and 68 sequence-related amplified polymorphism (SRAP) markers using a doubled-haploid (DH) population of 276 lines derived from the cross H155 × Qva. This map covered 1382.8 cM with an average marker interval of 7.9 cM. In total, 13 QTLs for pod-shatter resistance were identified in this DH population at two experimental sites (in Wuhan and Zhengzhou); three of the QTLs were present at both locations. At Zhengzhou, nine QTLs, identified in linkage groups A1, A7, A8, C5, and C8, together explained 49.0% of the phenotypic variation. At Wuhan, four QTLs were mapped on the A1, A4, A7, and C8 linkage groups. These QTLs explained 38.6% of the phenotypic variation. These results may serve as a valuable basis for further molecular dissection of pod-shatter resistance in B. napus, and for development of the markers related to QTLs that may be useful for marker-assisted selection of pod-shatter resistant cultivars.

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Mapping of imprinted quantitative trait loci (iQTLs) is helpful for understanding the effects of genomic imprinting on complex traits in animals and plants. At present, the experimental designs and corresponding statistical methods having been proposed for iQTL mapping are all based on temporary populations including F2 and BC1, which can be used only once and suffer some other shortcomings respectively. In this paper, we propose a framework for iQTL mapping, including methods of interval mapping (IM) and composite interval mapping (CIM) based on conventional low-density genetic maps and point mapping (PM) and composite point mapping (CPM) based on ultrahigh-density genetic maps, using an immortalized F2 (imF2) population generated by random crosses between recombinant inbred lines or doubled haploid lines. We demonstrate by simulations that imF2 populations are very desirable and the proposed statistical methods (especially CIM and CPM) are very powerful for iQTL mapping, with which the imprinting effects as well as the additive and dominance effects of iQTLs can be unbiasedly estimated.