Primary Investigation Of Mechanisms Of Oil Content Differences In Four Oilseed Crops

Edible plant oil is one of three major nutrient substance of human being. Formation ofseed oil as a storage matter involves a series of physiological and biochemical reactions,including photosynthesis. Almost every step of plant lipid synthesis in different cells andtheir organelles has been well-understood. However, regulation of difference in oil contentamong oilseed crops such as soybean (20%oil), rapeseed (40%), peanut (50%) and sesame(60%) is unclear. In this study I conducted a series of experiments including measurements ofoil accumulation-associated physiological factors and expression of selected candidate genesrelated to photosynthesis and oil biosynthesis in order to provide primary insights intoregulatory mechanisms of oil content difference in different oilseed crops and thus provideinformation for genetic improvement of oil content.Firstly, we performed experiments of measurements of photosynthesis efficiency andbiomass in four oilseed crops, and effects of light shading of pods and blocking of siliquehandle phloem on oil content. The results indicated:(1) The photosynthesis efficiency of fourcrops was: peanut>sesame>peanut>rapeseed, and positively correlated to the oil contentgradient. This may imply that the higher photosynthesis efficiency can provide more carbonsource for oil accumulation;(2) The biomass measurement shows that the accumulation ofcarbon in seed are obviously higher than other tissues (root, stem and leaf), indicating thatpartitioning of the carbon source is a key for higher oil content;(3) photosynthesis of siliquewas very important for seed development and oil accumulation;(4) blocking of silique handlephloem didn’t show obvious effect on seed oil content.Secondly, we detected and compared expression of selected candidate genes related tophotosynthesis (5genes: Rubisco activase, Rubisco large chain, Rubisco small chain,sedoheptulose-1,7-biphosphatase, Phosphoribulokinase) and fatty acid biosynthesis (16genes: ACAT2、BCCP1、FAB2、FabG、KASI、KAS2-FAB1、LACS9、LACS8、ACP、MOD1、DGAT1、Oleosin、FAD2、KAT2、LECITHIN、MCMT) in the leaf and at the three stages ofseed development.(1) We quantified the absolute quantity of gene expression for comparablegene expression among four oil crops;(2) expression of the genes related to photosynthesiswas positively correlated to the oil content of four oil crops, from the observation that theirhigh expression in crops with higher oil content. Expression quantity of Rubisco activasegene in leaf and at the three stages of seed development was:sesame/peanut>soybean>rapeseed, in agreement with pattern of photosynthesis efficiency;(3)The genes (BCCP1、FAB2、FabG、LACS8、ACP2、MOD1、Oleosin、FAD2、MCMT) relatedto oil biosynthesis usually expressed higher in sesame and much lower in rapeseed. A geneKAT2, belonging to TAG/fatty acid degradation pathway, showed lower expression than othergenes belonging to oil accumulation, which may be associated with higher oil contentformation;(4) PEPC (phosphoenolpyruvate carboxylase) participates in control of the fluxpartition of sugar into fatty acid biosynthesis and protein biosynthesis, and so it can affect oilcontent accumulation. We identified PEPC genes from four oil crops, and characterizedamino acid sequences, structure, identity and evolution of the genes. We also found that thesegenes had species-specific expression pattern in four oil corps and may play an important rolein seed development and oil accumulation.The results presented in this study on mechanisms of difference in oil content among fouroil crops will be helpful for further investigation of the genetic basis and molecularmechanisms of oil accumulation.