磷是植物生長發(fā)育所必需的一種大量元素,植物對磷素的有效性利用是提高植物產(chǎn)量的關(guān)鍵。細胞內(nèi)大量的磷素用于細胞膜磷脂的合成,細胞膜磷脂是細胞內(nèi)磷素的儲存庫。植物在缺磷條件下,膜磷脂會被磷脂酶水解釋放出磷素供其他必需含磷物質(zhì)(如DNA、RNA、ATP和蛋白質(zhì)等)的合成,植物通過該機制適應磷素的缺乏,這一代謝過程通過多個關(guān)鍵磷脂酶完成。
非特異性磷脂酶C4(NPC4)是植物NPC家族中活性最強的,在缺磷條件下被誘導表達最高的一個基因。NPC4在植物缺磷條件下的代謝功能尚不清楚,解析NPC4代謝功能的分子生化機制對植物磷素的高效利用意義重大。
在該研究中,研究者通過擴大擬南芥缺磷條件下脂質(zhì)組的檢測,發(fā)現(xiàn)植物特有的鞘磷脂糖基肌醇磷酸神經(jīng)酰胺(glycosyl inositol phosphoryl ceramide,GIPC)在缺磷條件下會顯著下降,同時根中鞘糖脂葡萄糖神經(jīng)酰胺(glucosylceramide,GlcCer)會大幅度上升。研究者檢測了缺磷條件下npc4體內(nèi)的鞘脂變化情況,發(fā)現(xiàn)與野生型(WT)相比,缺磷條件下npc4中GIPC的含量顯著高于WT,同時GlcCer的含量則顯著低于WT,缺磷條件下NPC4的缺失導致鞘脂代謝受阻。研究者進一步通過體外酶活實驗分析發(fā)現(xiàn)NPC4可將GIPC水解形成羥基神經(jīng)酰胺(hydroxyceramide,hCer)和帶磷酸基團的極性頭部。基因表達分析表明擬南芥在缺磷條件下NPC4和GCS(glucosylceramide synthase,葡萄糖神經(jīng)酰胺合成酶)會被大量誘導表達,誘導的GCS將NPC4水解GIPC生成的hCer轉(zhuǎn)化為GlcCer。這些研究結(jié)果表明NPC4水解GIPC,介導了缺磷條件下鞘磷脂到鞘糖脂的轉(zhuǎn)化。
GIPC是植物特有的一種鞘脂,含量占鞘脂總量的60%以上。GIPC是植物細胞膜的重要組成部分,通常與固醇和跨膜蛋白等形成細胞膜上特殊的抗去污劑結(jié)構(gòu)-脂筏,在植物細胞對外界信號響應上發(fā)揮著重要作用。亞細胞定位結(jié)果證明NPC4定位于細胞質(zhì)膜(PM),同時可在細胞膜蛋白提取物抗去污劑組分中檢測到NPC4-GFP,將分離的細胞質(zhì)膜蛋白通過蔗糖梯度離心分離,可在脂筏組分中檢測到NPC4-GFP。同時脂質(zhì)分析發(fā)現(xiàn)NPC4-GFP可與GIPC共定位,進一步證明了脂筏定位的NPC4可通過水解脂筏中的GIPC使細胞適應缺磷脅迫。
英文摘要(Abstract)
Phosphate is a vital macronutrient for plant growth, and itsavailabilityin soil is critical for agricultural sustainability and productivity.Asubstantial amount of cellular phosphate is used to synthesize phospholipidsforcell membranes. Here we identify a key enzyme, nonspecific phospholipaseC4(NPC4), that is involved in phosphosphingolipid hydrolysis and remodelinginArabidopsis during phosphate starvation. The levelofglycosylinositolphosphorylceramide (GIPC), the most abundant sphingolipid inArabidopsis thaliana, decreasedupon phosphate starvation. NPC4was highlyinduced by phosphate deficiency, and NPC4 knockouts in Arabidopsis decreasedthe loss ofGIPC and impeded root growth during phosphate starvation. Enzymaticanalysisshowed that NPC4 hydrolyzed GIPC and displayed a higher activity towardGIPC asa substrate than toward the common glycerophospholipidphosphatidylcholine.NPC4 was associated with the plasma membrane lipid rafts inwhich GIPC ishighly enriched. These results indicate that NPC4 uses GIPC as asubstrate inplanta and the NPC4-mediated sphingolipid remodeling plays apositive role inroot growth in Arabidopsis response to phosphate deficiency.
論文鏈接:https://academic.oup.com/plcell/advance-article/doi/10.1093/plcell/koaa054/6094430
相關(guān)評論鏈接:https://academic.oup.com/plcell/advance-article/doi/10.1093/plcell/koaa057/6094428