姜 凌, 張春義

中國(guó)農(nóng)業(yè)科學(xué)院生物技術(shù)研究所, 北京 100081

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植物維生素生物強(qiáng)化進(jìn)展

姜 凌, 張春義*

中國(guó)農(nóng)業(yè)科學(xué)院生物技術(shù)研究所, 北京 100081

維生素是動(dòng)植物生長(zhǎng)發(fā)育所必需的微量營(yíng)養(yǎng)素，包括A、B族(B1、B2、B3、B5、B6、B7、B9、B12)、C、D、E和K等。這些物質(zhì)由于人體內(nèi)不能合成或合成量不足，所以雖然需要量很少，但必須從膳食特別是植物性食品中獲得。因此，利用生物強(qiáng)化技術(shù)來(lái)提高植物合成的維生素含量可以有效地應(yīng)對(duì)全球性維生素缺乏的問題，對(duì)人類的生存與健康具有重要意義。綜述了近年來(lái)國(guó)內(nèi)外植物中維生素代謝和生物強(qiáng)化的主要研究成果，并對(duì)利用分子設(shè)計(jì)育種進(jìn)行維生素生物強(qiáng)化的未來(lái)發(fā)展方向進(jìn)行了展望。

維生素；代謝；植物；生物強(qiáng)化

維生素(vitamin)是指人體不可缺少的、必須通過(guò)膳食來(lái)獲得的小分子化合物，對(duì)預(yù)防營(yíng)養(yǎng)缺乏性疾病非常重要。目前確認(rèn)的人體必需維生素包括4種脂溶性維生素(維生素A、D、E、K)和9種水溶性維生素(維生素B1、B2、B3、B5、B6、B7、B9、B12和維生素C)。人體可以合成維生素D和維生素B12，但合成量不足以滿足人體的需求；其余的維生素雖然不能在人體內(nèi)合成，但可以在細(xì)菌、真菌和植物中合成并積累，而且維生素也是這些物種生長(zhǎng)發(fā)育所必需的微量營(yíng)養(yǎng)物質(zhì)[1]。

維生素通常作為酶學(xué)反應(yīng)的催化劑、輔酶或者輔酶的一部分，對(duì)人體和植物的生長(zhǎng)發(fā)育都非常重要。在人體中維生素的缺乏通常會(huì)引起營(yíng)養(yǎng)缺乏性疾病，如腳氣病(維生素B1，硫胺焦磷酸)、糙皮病(維生素B3，煙酸)、貧血(維生素B6，吡哆醛)、壞血癥(維生素C，抗壞血酸)和軟骨病(維生素D)。同時(shí)葉酸(維生素B9)攝取不足會(huì)引發(fā)巨幼紅細(xì)胞貧血和胎兒神經(jīng)管發(fā)育缺陷；維生素A的缺乏導(dǎo)致全球上億兒童有失明和易感疾病的風(fēng)險(xiǎn)；而維生素K的缺乏會(huì)導(dǎo)致中風(fēng)風(fēng)險(xiǎn)的增加[1]。為了減少營(yíng)養(yǎng)缺乏性疾病發(fā)生的風(fēng)險(xiǎn)，在發(fā)達(dá)國(guó)家中人們可以在食物中添加人工維生素或增加膳食的豐富性，但在發(fā)展中國(guó)家，數(shù)以億計(jì)的人們由于饑餓和營(yíng)養(yǎng)不良導(dǎo)致了維生素與礦物質(zhì)的多重營(yíng)養(yǎng)缺乏癥。近些年，人們通過(guò)對(duì)慢性疾病(如心血管疾病、癌癥、糖尿病、肥胖、骨質(zhì)疏松和牙周炎)成因的了解，發(fā)現(xiàn)植物性膳食不僅能滿足溫飽，更重要的是為人體提供了必需營(yíng)養(yǎng)素、防止?fàn)I養(yǎng)缺乏造成的疾病[2]。因此，利用現(xiàn)代農(nóng)業(yè)生物技術(shù)來(lái)提高植物維生素含量可以有效應(yīng)對(duì)全球性維生素缺乏的問題，對(duì)人類的生存與健康具有重要意義。本文綜述了近年來(lái)國(guó)內(nèi)外植物中維生素代謝和生物強(qiáng)化的主要研究成果，并展望了利用分子設(shè)計(jì)育種來(lái)進(jìn)行維生素生物強(qiáng)化的未來(lái)發(fā)展方向。

1 維生素的功能

維生素在各個(gè)物種中通常作為催化劑、輔酶或者輔酶的一部分參與酶學(xué)反應(yīng)，此外人體中維生素C和E還具有抗氧化的作用、β-胡蘿卜素與維生素D在動(dòng)物血液中一起參與鈣和磷的動(dòng)態(tài)平衡[1]。除了維生素D和維生素B12之外，人類不能自身制造其他任何一種人體必需的維生素，但其原因只在少數(shù)維生素中被研究過(guò)。例如，人類由于L-古洛糖酸內(nèi)酯氧化酶(L-gulonolactone oxidase, GULO)基因發(fā)生了嚴(yán)重突變，導(dǎo)致無(wú)法合成GULO酶，也就無(wú)法制造維生素C[3]；人體中也缺乏有功能的二氫新蝶呤醛縮酶(dihydroneopterin aldolase, DHNA)、二氫蝶呤羥甲基焦磷酸激酶/二氫蝶呤合成酶(hydroxymethyldihydropterin pyrophosphokinase/dihydropteroate synthase, HPPK /DHPS)、分支酸合成酶(4-aminodeoxychorismate synthase, ADCS)、分支酸裂解酶(4-aminodeoxychorismate lyase, ADCL)和二氫葉酸合成酶(dihydrofolatesynthetase, DHFS)而導(dǎo)致必須從膳食中攝取葉酸[4]。因此科學(xué)家為了應(yīng)對(duì)全球性維生素缺乏的問題，在植物維生素代謝領(lǐng)域開展了多方面的工作：一方面植物維生素代謝得到更多地闡釋，關(guān)鍵酶基因不斷地被克?。涣硪环矫嫒藗兝毛@得的植物維生素的新知識(shí)，不斷探討如何將傳統(tǒng)育種和分子育種結(jié)合以通過(guò)獲得高品質(zhì)的植物來(lái)源的天然維生素來(lái)有效應(yīng)對(duì)全球性維生素缺乏的問題[2]。

目前已經(jīng)對(duì)各類維生素在植物器官水平和亞細(xì)胞水平的貯存位置有了比較清楚的了解：β-胡蘿卜素主要在葉片和胡蘿卜的塊莖中富集；α-胡蘿卜素富集在果實(shí)和胡蘿卜的塊莖中；β-玉米黃質(zhì)主要在果實(shí)、種子和花中富集；這些化合物都儲(chǔ)存在有色質(zhì)體中。B族維生素主要聚集在種子中，在細(xì)胞質(zhì)、葉綠體和線粒體中都存在；種皮中維生素B1和維生素B3的含量尤其高。維生素C主要貯存在果實(shí)中，位于葉綠體、非原質(zhì)體、細(xì)胞質(zhì)和液泡中。維生素E主要在油料作物的種子中富集，位于葉綠體和脂質(zhì)體中；所有綠色蔬菜和胡蘿卜中都含有葉綠醌(維生素K1)，其主要存在于葉綠體和質(zhì)膜上[5]。同時(shí)研究發(fā)現(xiàn)植物維生素代謝網(wǎng)絡(luò)具有一些共性：①多種維生素的合成有著共同的碳水化合物來(lái)源；②多種維生素的合成具有共同的中間產(chǎn)物；③維生素合成的關(guān)鍵反應(yīng)中必需有其他維生素的參與；④氨基酸代謝與維生素代謝密切相關(guān)[5]。由于這種網(wǎng)絡(luò)內(nèi)代謝的復(fù)雜性，改變一條維生素代謝通路常常伴隨著其他維生素代謝通路的協(xié)同反應(yīng)，例如在土豆塊莖中過(guò)表達(dá)玉米黃質(zhì)環(huán)氧化酶會(huì)導(dǎo)致玉米黃素和生育酚的含量同時(shí)增加[6]；擬南芥中過(guò)表達(dá)生育酚環(huán)化酶基因使δ-生育酚含量增加了幾倍，而維生素C含量卻減少了60%[7]。這種調(diào)控機(jī)制可能是由于代謝底物的利用效率改變，也可能是產(chǎn)物對(duì)酶學(xué)反應(yīng)的反饋抑制，或維生素小分子與基因的mRNA直接發(fā)生的核開關(guān)調(diào)控，上述可能性都非常值得探討。上述新知識(shí)的獲得都為人們?cè)谥参镏羞M(jìn)行維生素強(qiáng)化打下了深厚的研究基礎(chǔ)。

目前維生素生物強(qiáng)化常用4種策略：①增強(qiáng)限速步驟的酶活性；②過(guò)表達(dá)反應(yīng)的第一步；③抑制代謝支路；④增加代謝物的儲(chǔ)藏空間[8]。下面將逐步介紹植物中各類維生素生物強(qiáng)化的研究進(jìn)展。

2 植物中維生素生物強(qiáng)化進(jìn)展

2.1 維生素A

維生素A是類視黃酮的總稱，蔬果中的維生素A原(類胡蘿卜素)可以在人體內(nèi)轉(zhuǎn)化為維生素A。類胡蘿卜素廣泛存在于蔬果中，如橙子、西蘭花、菠菜、胡蘿卜、南瓜等；土豆、大麥和小麥中含量低；而在水稻和小米中很難被檢測(cè)到。植物中的類胡蘿卜素有4類：α-胡蘿卜素、β-胡蘿卜素、γ-胡蘿卜素和β-核黃素[9]。目前作物中維生素A原的生物強(qiáng)化中的重大技術(shù)突破就是黃金大米(golden rice)。八氫番茄紅素去飽和酶(phytoenedesaturase, Crt1/PSY)在植物體內(nèi)的過(guò)表達(dá)可以使水稻中類胡蘿卜素的含量明顯提高[10,11]。其中第二代黃金稻米的類胡蘿卜素含量高達(dá)37 μg/g，而且84%為β-胡蘿卜素[11]。目前臨床試驗(yàn)表明第二代黃金稻米中的β-胡蘿卜素能有效地轉(zhuǎn)化為視黃醇，是一種優(yōu)良的維生素A原[12,13]。類似的策略在油菜籽、胡麻籽、土豆、番茄、玉米和大豆中都獲得了成功[14～20]。最新的報(bào)道顯示，使用基因槍技術(shù)將融合了來(lái)自豌豆的葉綠體定位信號(hào)和菠蘿泛菌的八氫番茄紅素合成酶基因crtB轉(zhuǎn)化大豆時(shí)，其種子中的β-胡蘿卜素提高了1 500倍[20]。

還有兩種提高類胡蘿卜素含量的方法：①抑制番茄紅素環(huán)化酶(lycopene β-cyclase， LYCB)和β-胡蘿卜素羥化酶(β-carotene hydroxylase，HYDB)基因的轉(zhuǎn)錄水平使得代謝流朝形成β-胡蘿卜素的方向進(jìn)行，這個(gè)策略在土豆、紅薯和小麥中得到成功應(yīng)用[21～24]；②調(diào)節(jié)橙色(Or)基因的活性。Or基因在橙色果肉的紅薯中負(fù)責(zé)類胡蘿卜素的積累，而且Or蛋白與PSY蛋白物理互作，可以在翻譯后水平上增加PSY蛋白的穩(wěn)定性和活性[25]。這個(gè)策略在紅薯、土豆、花菜和番茄中均獲得成功應(yīng)用[26～31]。

不過(guò)上述策略也有不足之處。例如在番茄中類胡蘿卜素基因過(guò)表達(dá)時(shí)，種子中的核黃素、β-胡蘿卜素和玉米黃質(zhì)的含量有所增加，但伴隨著赤霉素含量的減少，導(dǎo)致植株的矮化[19]。因此，代謝工程育種會(huì)由于人們對(duì)內(nèi)源代謝調(diào)控和基因表達(dá)的時(shí)空差異的了解有限而受到限制[32]。利用全基因組關(guān)聯(lián)分析(genome-wide association studies，GWAS)可以確認(rèn)更多的天然等位變異，從而通過(guò)不同位點(diǎn)優(yōu)異等位基因的聚合協(xié)助維生素A原的強(qiáng)化。

由于玉米的遺傳多樣性比較豐富，通過(guò)GWAS來(lái)明確調(diào)控類胡蘿卜素含量積累的工作主要在玉米中開展。目前了解到PSY的轉(zhuǎn)錄水平與類胡蘿卜素的含量正相關(guān)，而編碼類胡蘿卜素合成的基因、編碼玉米黃質(zhì)氧化酶基因與類胡蘿卜素的含量呈負(fù)相關(guān)[32]。此外研究者還發(fā)現(xiàn)很多參與類胡蘿卜素代謝基因的優(yōu)良等位變異與控制β-胡蘿卜素含量的數(shù)量性狀遺傳位點(diǎn)(quantitative trait loci，QTL)緊密關(guān)聯(lián)[32～34]。這意味著如果通過(guò)天然變異找到合適的供體親本可以加速維生素A原的生物強(qiáng)化。目前利用分子輔助育種技術(shù)已經(jīng)分別了獲得了富含β-胡蘿卜素的大田玉米和富含玉米黃質(zhì)的甜玉米[35,36]。

在水稻中的最新研究表明，在黃金大米2號(hào)的基礎(chǔ)上的多基因策略可以使胚乳中總類胡蘿卜素的含量提高6倍。這個(gè)策略中分別表達(dá)了2個(gè)不同的酶：①擬南芥來(lái)源的1-脫氧木酮糖-5-磷酸合酶(1-deoxy-D-xylulose-5-phosphate synthase，AtDXS)，它在赤蘚醇磷酸合成途徑中可以生成類胡蘿卜素的前體，說(shuō)明類異戊二烯底物的增加可以導(dǎo)致最終產(chǎn)物的增加；②擬南芥來(lái)源的橙色基因(AtOr)，這個(gè)基因的導(dǎo)入可以使胚乳中儲(chǔ)藏類胡蘿卜素的空間增大[37]。上述結(jié)果表明確認(rèn)代謝途徑的瓶頸可以精確調(diào)整生物強(qiáng)化的策略，從而提高作物中維生素A原的含量。

2.2 葉酸

葉酸是一種非常重要的水溶性B族維生素，包括四氫葉酸及其系列衍生物。它作為一碳單位的供體參與很多代謝反應(yīng)。細(xì)菌、真菌和植物都可以合成葉酸，細(xì)菌和真菌都在細(xì)胞質(zhì)中合成葉酸，而植物中的葉酸分別在細(xì)胞質(zhì)、線粒體和質(zhì)體中合成[38]。

研究者們?cè)诜?、水稻、玉米、生菜、土豆和墨西哥豆中都進(jìn)行過(guò)葉酸強(qiáng)化[17,39～43]。一般有兩種策略：①過(guò)表達(dá)葉酸合成的限速酶DHFS，在玉米中過(guò)表達(dá)可以使葉酸含量提高2倍[17]；②過(guò)表達(dá)葉酸合成支路的第一步反應(yīng)酶。例如，過(guò)表達(dá)細(xì)胞質(zhì)中的GTP環(huán)化酶(GTP cyclohydrolase I，GTPCHI)可以使番茄中的葉酸含量提高2倍、生菜中提高8.5倍、墨西哥豆中提高150倍[40～42]。與ADCS的轉(zhuǎn)基因植株雜交，土豆中葉酸含量提高到原來(lái)的3倍、番茄提高到原來(lái)的25倍、水稻中提高到原來(lái)的100倍[39,40,47]。擬南芥來(lái)源的葉酰谷氨酸聚合酶和哺乳動(dòng)物來(lái)源的葉酸結(jié)合蛋白在葉酸強(qiáng)化的水稻中過(guò)表達(dá)可以增加葉酸的儲(chǔ)藏穩(wěn)定性[44]。而且葉酸強(qiáng)化的番茄和水稻也被證實(shí)可以提高人們體內(nèi)的葉酸含量[45,46]。上述結(jié)果說(shuō)明對(duì)作物進(jìn)行更有效的葉酸強(qiáng)化需要對(duì)植物的葉酸代謝途徑進(jìn)行更深入的研究[39]。

2.3 其他B族維生素

其他B族維生素包括維生素B1(硫胺素類化合物)、維生素B2(核黃素類化合物)、維生素B3(煙酸)、維生素B5(泛素)、維生素B6(吡哆醛、吡哆醇、吡哆胺及其磷酸化的衍生物)、維生素B7(生物素)和維生素B12(鈷胺素)。到目前為止，已有研究只在擬南芥中進(jìn)行過(guò)維生素B1和維生素B6的表達(dá)[47～50]。在維生素B1途徑中磷酸甲基嘧啶合成酶(phosphomethylpyrimidine synthase，THIC)過(guò)表達(dá)后可以使硫胺素類化合物的含量有一些提高[47]，但這種維生素B1的動(dòng)態(tài)平衡能否在作物中實(shí)現(xiàn)還很難確定[48]。維生素B6是一大組水溶性的同效維生素，其中磷酸吡哆醛是超過(guò)140個(gè)細(xì)胞內(nèi)酶學(xué)反應(yīng)的輔酶，是主要的有效形式[49]。近年來(lái)有幾個(gè)研究小組在擬南芥中過(guò)表達(dá)了吡哆醛磷酸合成酶(pyridoxal phosphate synthase，PDX)基因，但效果還不明顯[50]。上述結(jié)果說(shuō)明人們需要對(duì)B族維生素在植物體內(nèi)的調(diào)控機(jī)制進(jìn)行更深入的研究，才能進(jìn)一步明確其在植物中的生物強(qiáng)化策略。

2.4 維生素C

維生素C又名抗壞血酸，在植物中主要有多條途徑來(lái)生成維生素C，其中葡萄糖-6-磷酸是Smirnoff-Wheeler途徑的底物、半乳糖醛酸是果膠降解途徑的底物、肌醇是類動(dòng)物途徑的底物[51]。目前對(duì)植物維生素C含量的改良策略有3種：①提高合成途徑關(guān)鍵酶基因的表達(dá)水平；②促進(jìn)維生素C的再生循環(huán)，提高還原抗壞血酸和脫氫抗壞血酸的比例；③利用轉(zhuǎn)錄因子整體強(qiáng)化維生素C的代謝途徑。利用維生素C合成途徑和再循環(huán)利用途徑的關(guān)鍵基因在番茄、土豆、玉米和草莓中都已經(jīng)進(jìn)行過(guò)維生素C的生物強(qiáng)化[17,52,58]。其中使用過(guò)的基因分別編碼GDP-甘露糖焦磷酸化酶(GDP-mannose pyrophosphorylase，GMPase)、阿拉伯糖內(nèi)酯氧化酶(arabinono-1,4-lactone oxidase，ALO)、肌醇加氧酶2(myo-inositol oxygenase 2，MIOX2)、GDP-甘露糖差相異構(gòu)酶(GDP-mannose epimerase，GME)、半乳糖醛酸還原酶(galacturonatereductase，GaIUR)、L-古洛糖酸內(nèi)酯氧化酶(L-gulono-1,4-γ-lactone oxidase，GuLO)和GDP-L-半乳糖磷酸化酶(galactosephosphorylase，GGP)[52,54,56,57,59,60]。其中目前發(fā)現(xiàn)的能使維生素C含量提高的最有效的方法是GGP的過(guò)表達(dá)，該方法能使獼猴桃的維生素C含量提高4倍，如果GGP和GME在煙草中共表達(dá)，其葉片的維生素C含量可以提高12倍[59]。在第2個(gè)策略的應(yīng)用中，降低單脫氫抗壞血酸還原酶(monodehydroascorbatereductase，MDHAR)的轉(zhuǎn)錄水平可以使番茄中的抗壞血酸含量增加[55]；在玉米和土豆中過(guò)表達(dá)脫氫抗壞血酸還原酶(dehydroascorbatereductase，DHAR)可以使植物的葉片、籽粒和塊莖中的抗壞血酸含量明顯增加[17,53,58]。在第3個(gè)策略的應(yīng)用中發(fā)現(xiàn)過(guò)表達(dá)擬南芥中轉(zhuǎn)錄因子AtERF98可以使甘露糖/半乳糖途徑中的許多關(guān)鍵基因和肌醇合成途徑的MIOX4轉(zhuǎn)錄水平升高進(jìn)而導(dǎo)致抗壞血酸含量的增加[60]。但主要糧食作物中維生素C的生物強(qiáng)化鮮見報(bào)道。

2.5 維生素E

維生素E對(duì)人類的膳食和健康都非常重要，外源的維生素E通過(guò)肝臟吸收[61]。植物是人類維生素E攝入的主要來(lái)源。維生素E包括生育酚和生育三烯酸，其中生育三烯酸是大多數(shù)單子葉植物和一部分雙子葉植物維生素E的主要形式[62]。在各類維生素E化合物中，α-生育酚可以被人類的α-生育酚轉(zhuǎn)運(yùn)蛋白協(xié)助，因此維生素E的生物強(qiáng)化主要指提高總的含量和α-生育酚所占比例[61]。

維生素E生物強(qiáng)化的目標(biāo)是提高維生素E的總量和改變維生素E各組分的比例，并將其他種類的生育酚類物質(zhì)轉(zhuǎn)化為活性最高的α-生育酚。維生素E生物強(qiáng)化主要利用單基因或多基因來(lái)進(jìn)行。在油菜、煙草、生菜、番茄、大麥、水稻、大豆和玉米中都已經(jīng)進(jìn)行過(guò)維生素E的生物強(qiáng)化，其中使用過(guò)的基因分別編碼生育酚環(huán)化酶(tocopherolcyclase，TC)、羥苯丙酮酸雙加氧酶(hydroxyphenylpyruvic acid dioxygenase，HPPD)、尿黑酸植基轉(zhuǎn)移酶(homogentisate phytyltransferase， HPT)、2-甲苯-6-葉綠基-1,4-苯醌甲基轉(zhuǎn)移酶(2-methyl-6-phytyl-1,4-benzoquinol methyltransferase，MPBQ-MT)、尿黑酸牛兒基牻牛兒基轉(zhuǎn)移酶(homogentisic acid geranylgeranyltransferase，HGGT)和γ-生育酚甲基轉(zhuǎn)移酶(γ-tocopherol methyltransferase，γ-TMT)[62～70]。其中，最成功的轉(zhuǎn)單基因應(yīng)用是花椰菜35S啟動(dòng)子驅(qū)動(dòng)的γ-TMT在植物中的過(guò)表達(dá)，植物種子中的α-生育酚的比例都得到了顯著提高，例如油菜中增加了6倍、輪葉黨參中增加了6.4倍、生菜中增加了2倍、紫蘇中增加了1.8倍、大豆中增加了4倍，擬南芥中增加了80倍[72～77]。

同時(shí)過(guò)表達(dá)多個(gè)基因可以使維生素E的含量得到顯著提高，并且增加了α-生育酚的比例[70,78～80]。油菜中同時(shí)過(guò)表達(dá)HPT和γ-TMT可以使維生素E的活性提高12倍，且?guī)缀跛笑?和δ-生育酚都轉(zhuǎn)化為α-生育酚和β-生育酚[78,79]。MT(VTE3)可以使大豆中的生育三烯酸比例由20%降低到2%，當(dāng)與γ-TMT結(jié)合在一起過(guò)表達(dá)時(shí)，種子聚集的α-生育酚占比高達(dá)95%，α-生育酚的含量增加了至少8倍，種子維生素E的活性增加了最高5倍[70,80]。酵母中的tyrA(編碼HPT)、擬南芥HPPD和HPT在大豆中過(guò)表達(dá)時(shí)，尿黑酸和生育酚在種子中的含量分別增加了800倍和15倍，維生素E的活性相對(duì)野生型增加了11倍[65]；煙草中使用同樣的策略時(shí)葉片總維生素E含量提高了約10倍[81]。不過(guò)在玉米中過(guò)表達(dá)擬南芥HPPD和MT后籽粒中只有γ-生育酚的含量增加了3倍，其他形式的維生素E都沒有被檢測(cè)到[82]；而土豆中使用過(guò)表達(dá)擬南芥的HPPD或HPT都無(wú)法使生育酚的比例發(fā)生任何變化[83]。在玉米中通過(guò)GWAS方法確認(rèn)了MT和γ-TMT的多個(gè)優(yōu)良等位位點(diǎn)與維生素E的含量密切相關(guān)[84,85]。這些結(jié)果說(shuō)明如果對(duì)植物的維生素E代謝調(diào)控有進(jìn)一步了解，可以確定更多適用于生物強(qiáng)化的候選基因。

3 展望

聯(lián)合國(guó)糧農(nóng)組織(Food and Agriculture Organization of the United Nations，F(xiàn)AO)倡導(dǎo)，發(fā)展以食物為基礎(chǔ)的營(yíng)養(yǎng)型農(nóng)業(yè)以減少人體微量營(yíng)養(yǎng)素缺乏的狀況。人們應(yīng)按自己喜好通過(guò)豐富膳食種類、改變生活方式和增加運(yùn)動(dòng)來(lái)提高微量營(yíng)養(yǎng)素的攝入[86]。膳食中過(guò)量添加的人工葉酸能影響人類DNA甲基化水平，與結(jié)腸癌和前列腺癌的患病率有一定的相關(guān)性[87,88]。因此，培育富含維生素的作物新品種具有非常廣泛的應(yīng)用前景。

有報(bào)道顯示，發(fā)達(dá)國(guó)家(德國(guó)、英國(guó)、芬蘭和美國(guó))人群維生素?cái)z入水平仍低于推薦水平，說(shuō)明盡管有豐富的食品可供選擇，人體對(duì)維生素的需求和實(shí)際攝入量之間仍存在明顯差距[89]。目前很多生物強(qiáng)化的食物不需要蒸煮就可以被人們食用, 維生素生物強(qiáng)化的糧食作物可以對(duì)人體營(yíng)養(yǎng)和健康產(chǎn)生積極影響[90]。不過(guò)到目前為止，還沒有更好的可用于維生素B1、維生素B6和維生素C的技術(shù)策略。如果未來(lái)能將遺傳網(wǎng)絡(luò)、生化功能和分子機(jī)理有機(jī)地結(jié)合在一起，并借助同位素標(biāo)記的代謝組學(xué)、代謝產(chǎn)物與大分子的互作和代謝產(chǎn)物與小分子互作等技術(shù)手段來(lái)進(jìn)一步理解植物維生素代謝調(diào)控的過(guò)程，則未來(lái)的植物維生素生物強(qiáng)化將會(huì)有更加廣闊的前景。

由于維生素是人體的必需微量營(yíng)養(yǎng)元素，未來(lái)針對(duì)植物的維生素生物強(qiáng)化可以考慮針對(duì)人體的個(gè)性化需求來(lái)培育生物強(qiáng)化作物：①通過(guò)全基因組測(cè)序?qū)⒔⒆魑锏臓I(yíng)養(yǎng)單倍型，進(jìn)一步了解性狀形成的遺傳機(jī)制; ②通過(guò)大數(shù)據(jù)的挖掘確認(rèn)與營(yíng)養(yǎng)相關(guān)的表型，結(jié)合代謝組和GWAS明確作物的優(yōu)良等位變異; ③通過(guò)代謝組學(xué)技術(shù)明確維生素代謝的中間產(chǎn)物和反應(yīng)的限速步驟; ④明確設(shè)計(jì)特定的轉(zhuǎn)基因策略和途徑。最終，維生素強(qiáng)化的作物將能夠滿足人們對(duì)營(yíng)養(yǎng)的個(gè)性化需求，在提高人類健康水平方面做出重要貢獻(xiàn)。

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Progress on Vitamins Fortification in Plants

JIANG Ling, ZHANG Chun-yi*

BiotechnologyResearchInstitute,ChineseAcademyofAgriculturalSciences,Beijing100081,China

Vitamins are vital nutrients that plants and animals require in limited amounts, including A, B1, B2, B3, B5, B6, B7, B9, B12, C, D, E and K. Human cannot synthesize the compounds in sufficient quantities, and they must be obtained from the diet, especially from plant foods. Vitamin deficiency is still prevalent in large population across the world, and closely associated with increasing risks of diseases. Scientists have made great efforts on the enhancement of vitamins in plants through biofortification to tackle this global problem. This review summarized the progress of vitamin metabolism and fortification in plants, and sheds light on the trends in breeding by molecular design for vitamin-enriched crops.

vitamin; metabolism; plant; biofortification

2016-09-18; 接受日期：2016-10-19

國(guó)家973計(jì)劃項(xiàng)目(2013CB127003)資助。

姜凌，副研究員，主要從事植物生物強(qiáng)化研究。E-mail:jiangling@caas.cn。*通信作者：張春義，研究員，博士生導(dǎo)師，主要從事植物生物強(qiáng)化研究。E-mail:zhangchunyi@caas.cn

10.3969/j.issn.2095-2341.2016.06.01