碳/氮營養源對水稻懸浮細胞蔗糖轉運蛋白基因表現之調控

Abstract

碳水化合物的累積及運輸效能是決定作物產量的重要因素，目前已有研究指出低氮素或缺氮逆境會促進碳水化合物移往積儲組織及地下部。蔗糖為植物體中醣類運輸的主要形式，而蔗糖轉運蛋白 (sucrose transporter, SUT) 則為調控蔗糖進出韌皮部的主要蛋白質。本研究利用水稻 (Oryza sativa L. cv. Tainung 67) 懸浮細胞系統探討培養液中蔗糖、銨態氮及硝酸態氮含量改變對水稻蔗糖轉運蛋白基因家族成員OsSUT1、2、4及5表現之影響。研究結果顯示缺糖處理之下，細胞生長速度及細胞活力會極顯著下降，而OsSUT2、4及5的基因表現也隨之降低，但OsSUT1之基因表現則顯著誘導上升。在供糖處理之下，OsSUT2及4基因表現會受缺氮誘導，而此誘導現象於恢復供氮6小時後即消失，且銨態氮 (NH4+-N) 之效應較硝酸態氮 (NO3--N) 顯著。另一方面，OsSUT5之基因表現則受缺氮刺激所抑制，但於恢復供氮2天後可使OsSUT5基因表現回復，且NO3--N之效應較NH4+-N顯著。分析帶有不同OsSUT4啟動子長度片段接GUS報導基因之轉殖水稻懸浮細胞，發現OsSUT4啟動子上受缺氮調控之cis-acting elements位置可能位於OsSUT4轉譯起始點至上游434 bp間。

Accumulation and transport of carbohydrates are important for crop yield. Sucrose is the major sugar for long-distance translocation within plant tissue through phloem. Studies have suggested that nitrogen deficiency promotes translocation of non-structural carbohydrates to sink tissues in plants. Sucrose transporters (SUTs) play important roles in sucrose loading into phloem. In this study, effects of carbon and nitrogen nutrients on OsSUTs gene expressions in rice (Oryza sativa L.) suspension cells were investigated. The results showed that sucrose starvation significantly reduced cell growth rate and cell viability. Sucrose starvation also reduced OsSUT2, 4 and 5 expressions, but OsSUT1 gene expression was significantly induced in sucrose-starvated cells. In sucrose supplying condition, nitrogen starvation induced OsSUT2 and 4 gene expressions, and the effect was suppressed after 6 hours of nitrogen recovery treatment. The effect of nitrogen recovery treatment with ammonium (NH4+-N) on OsSUT2 and 4 gene expressions was more significant than that was treated with nitrate (NO3--N). On the other hand, OsSUT5 gene expression was inhibited under nitrogen starvation, but after nitrogen re-supplied for 2 days, OsSUT5 gene expression was increased to a level equivalent to control. Moreover, the NO3--N effect on OsSUT5 expression was more significant than NH4+-N. Based on OsSUT4 promoter activity analysis in transgenic rice suspension cells, it was suggested that the cis-acting elements related to nitrogen-starvation response were located at the region within 434 bp upstream of the translation start codon.