水稻淀粉合成的分子生物学研究进展

本文综述了水稻淀粉合成的分子生物学研究的最新进展,主要内容是参与淀粉合成的酶鉴定及其基因表达调控,也介绍了对这些酶的遗传操作改良稻米淀粉品质等内容。     

淀粉合酶的酶学与分子生物学研究进展

淀粉合酶作为淀粉合成的关键酶之一,一直是淀粉研究的重要内容。这些研究多集中在对其同工型的研究,淀粉合酶的两类主要同工型分别为淀粉粒结合的淀粉合酶和可溶性淀粉合酶,这两类同工型的作用极为复杂。本文介绍了淀粉合酶同工型的酶学和分子生物学近年来的研究进展,同时也讨论了这些同工型的分类、相互关系及其在淀粉合成过程中的生理功能等内容。     

淀粉合酶的酶学与分子生物学研究进展

淀粉合酶作为淀粉合成的关键酶之一,一直是淀粉研究的重要内容,这些研究多集中在对其同工型的研究,淀粉合酶的两类主要同工型分别为淀粉粒结合的淀粉合酶和可溶性淀粉合酶,这两类同工型的作用极为复杂,本文介绍了淀粉合酶同工型的酶学和分子生物学近年来的研究进展,同时也讨论了这些同工型的分类,相互关系及其在淀粉合成过程中的生理功能等内容。     

基因工程改良淀粉品质

淀粉对人类生活十分重要,它不仅是人们的能量和营养来源,而且还是重要的工业原材料。对于淀粉合成过程及淀粉的加工、使用一直是淀粉研究的重点内容。淀粉的合成在最后阶段涉及到３个关键性的酶是：ＡＤＰＧ焦磷酸化酶、淀粉合成酸以及淀粉分支酶。它们分别催化ＡＤＰ－葡萄糖的形成、葡聚糖链的延伸以及分支链的形成。另外淀粉去分支酶对淀粉最终结构的形成也起到重要作用。本文将介绍上述４个酶近年来的生物化学和分子生物学研究     

云南野生稻籽粒淀粉合成关键酶活性测定

为研究云南3种野生稻直链淀粉合成机制并利用其直链淀粉含量较低的优良品质,以云南3种野生稻和4种当地栽培稻为材料,研究野生稻灌浆期籽粒4种淀粉合成关键酶(包括ADPG焦磷酸化酶、可溶性淀粉合成、颗粒凝结型淀粉合成酶、淀粉分支酶)活性变化。结果表明,野生稻中4种淀粉合成酶的变化趋势与栽培稻相似,但活性有较大差别。颗粒凝结型淀粉合成酶的活性与直链淀粉含量呈正相关,说明在野生稻中同样是由颗粒凝结型淀粉合成酶控制直链淀粉的合成。同时发现在同一灌浆期,同种材料中可溶性淀粉合成酶和淀粉分支酶的活性变化呈相反趋势,推测这两种酶之间可能在淀粉合成过程中存在某种反馈调节机制。     

植物支链淀粉合成的关键酶——淀粉分支酶

支链淀粉是植物淀粉的主要成分,而淀粉分支酶是其合成的关键酶。淀粉分支酶可分为两同形体家族,本文从酶学特性、染色体定位、基因及基因表达方面阐明了它们之间的联系和区别,并证实不同同形体在植物支链淀粉合成和结构决定上所起作用不同。开展对该酶的深入研究不论是在基础理论研究领域还是在现实应用方面都具重要意义。     

水稻胚乳中淀粉合成相关酶活性的变化对支链淀粉精细结构的影响

分析了水稻（Oryza sativa L．）籽粒发育过程淀粉生物合成途径中的关键酶——ADP-葡萄糖焦磷酸化酶、可溶性淀粉合酶、淀粉分支酶以及淀粉脱支酶活性变化,同时研究了淀粉结构形成动态．与野生型晚粳9522相比,转基因晚粳9522中直链淀粉的合成被显著抑制,而总淀粉含量和籽粒终重量没有改变．淀粉生物合成途径中关键酶活性表达时间不一致,存在明显的时段特征,这与淀粉积累动态密切相关．可溶性淀粉合酶活性表达最早,其在灌浆前期驱动淀粉合成起始;而淀粉粒结合态淀粉合酶在胚乳发育的中期活性最大．两水稻实验材料间,除淀粉脱支酶活性变化有所不同外,ADP-葡萄糖焦磷酸化酶和淀粉分支酶活性的变化没有明显差异．并且,支链淀粉的分支模式在水稻籽粒发育过程中变化较大,且与品种有关．以上结果揭示,支链淀粉的合成要先于直链淀粉,并且在控制支链淀粉各分支的形成过程中有不同的酶在起特异的作用．     

植物支链淀粉生物合成研究进展

植物支链淀粉占贮存淀粉的70%～80%,是决定植物果实或种子品质的关键成分.对植物支链淀粉生物合成途径及其代谢酶基因的研究,可大大推动支链淀粉结构的改造和在食品工业上的应用.该文介绍了植物支链淀粉的结构组成,详细阐述了参与支链淀粉生物合成的三类酶,即淀粉分支酶(starch branchingenzyme,SBE)、可溶性淀粉合酶(soluble starch synthase,SSS)和淀粉脱支酶(starch debranching enzyme,SDBE)的编码基因、酶学特性及其在支链淀粉合成中的作用,并就植物支链淀粉的合成模型加以探讨.同时提出了该研究领域尚待解决的问题,对其应用前景作了展望.     

百合鳞茎发育过程中淀粉合成相关酶基因的克隆及表达分析

该研究通过同源克隆技术克隆腺苷二磷酸葡萄糖焦磷酸化酶(AGPase)、颗粒结合淀粉合酶(GBSS)和可溶性淀粉合酶(SSS) 3类百合淀粉合成关键酶基因,分析这三类淀粉合成关键酶基因的表达变化,测定百合鳞茎膨大发育中淀粉含量变化。结果表明:(1) AGPase具有GlgC家族蛋白PLN02241蛋白结构特征及cl11394家族蛋白ADP_Glucose_PP与NTP_transferase结构域,获登录号KP751443; GBSS与SSS具有cl10013家族蛋白Glyco_transf_5,GT1_Glycogen_synthase_DULL1_like结构域,获登录号分别为KP751444、KP751445。(2)百合鳞茎形成与膨大发育过程中,淀粉含量呈现递增趋势,鳞茎盘开始分化茎杆时其淀粉含量最高,达到44.52%。鳞茎与叶片部位的三个淀粉合成相关酶基因表达量均逐渐增加;在鳞茎膨大后茎杆分化阶段,三个淀粉合成相关酶基因表达量达到最高,AGPase、GBSS、SSS在鳞片中的表达量分别为10.79,6.92和5.12,叶片中的表达量分别为6.79,5.22和4.41,鳞片中的表达量大幅度高于叶片;淀粉合成相关酶基因的表达量变化与淀粉含量、鳞茎的膨大发育成正相关。这为鳞茎的繁殖生产提供了可通过调节淀粉合成关键酶基因表达促进百合鳞茎膨大发育的思路。     

禾谷类作物胚乳的淀粉合成

禾谷类作物胚乳拥有独特的淀粉合成途径,需要多种特异性同工酶的参与,这些酶在禾谷类其他组织或非禾谷类作物中是不存在的。近来明确了单个淀粉同工酶的功能,这有助于我们更深入地了解禾谷类淀粉直链、支链的合成与分布。在对禾谷类淀粉合成进行遗传分析的基础上,提出了脱分支酶作用模型。以水稻全基因组序列草图为背景,本文首次全面分析了禾谷类作物的淀粉合成。     

稻米淀粉品质形成的关键酶及其分子生物学研究进展

稻米淀粉的形成是影响水稻产量和品质的决定性因素之一。因此,开展稻米淀粉形成过程中所涉及关键酶的研究是非常必要的。随着分子生物学技术的快速发展,有关稻米淀粉品质的研究也越来越深入,并取得了较大进展。该文对水稻淀粉品质形成过程中的关键酶及其分子生物学研究进展进行了较为详尽的综述,主要包括ADP葡萄糖焦磷酸化酶、淀粉合成酶、淀粉分支酶和淀粉去分支酶等,并对该领域的发展趋势进行了展望。     

转基因技术改良稻米淀粉品质的研究进展

淀粉是稻米胚乳的主要组成成分, 而淀粉含量和性质的差异又直接决定稻米的品质。早期关于稻米淀粉的研究局限于其组成成分、品种间含量的差异以及稻米淀粉合成的经典遗传学方面。随着现代分子生物学和转基因技术的发展, 稻米品质、淀粉的生物合成及其分子调控成为研究热点。随着淀粉合成相关基因的克隆、分子特性及其表达调控的研究取得了较大进展, 人们也开始尝试利用现代基因工程技术, 高效地改良稻米品质, 如提高或降低淀粉含量及改变支链淀粉的结构。本文从综述稻米淀粉的组成、结构和淀粉合成相关酶的研究进展入手, 探讨了转基因技术改良稻米品质的研究进展和发展前景。     

稻米淀粉品质形成的关键酶及其分子生物学研究进展

稻米淀粉的形成是影响水稻产量和品质的决定性因素之一。因此, 开展稻米淀粉形成过程中所涉及关键酶的研究是非常必要的。随着分子生物学技术的快速发展, 有关稻米淀粉品质的研究也越来越深入, 并取得了较大进展。该文对水稻淀粉品质形成过程中的关键酶及其分子生物学研究进展进行了较为详尽的综述, 主要包括ADP葡萄糖焦磷酸化酶、淀粉合成酶、淀粉分支酶和淀粉去分支酶等, 并对该领域的发展趋势进行了展望。     

Effects of the activities of key enzymes involved in starch biosynthesis on the fine structure of amylopectin in developing rice (Oryza sativa L.) endosperms

The dynamic changes of the activities of enzymes involving in starch biosynthesis, including ADP-glucose pyrophosphorylase (AGPase), soluble starch synthases (SSS), starch branching enzyme (SBE) and starch debranching enzymes (DBE) were studied, and changes of fine structure of amy- lopectin were characterized by isoamylase treatment during rice grain development, using trans anti-waxy gene rice plants. The relationships between the activities of those key enzymes were also analyzed. The amylose synthesis was significantly inhibited in transgenic Wanjing 9522, but the total starch content and final grain weight were less affected as compared with those of non-transgenic Wanjing 9522 rice cultivar. Analyses on the changes of activities of enzymes involving in starch bio- synthesis showed that different enzyme activities were expressed differently during rice endosperm development. Soluble starch synthase is relatively highly expressed in earlier stage of endosperm de- velopment, whilst maximal expression of granule-bound starch synthase (GBSS) occurred in mid-stage of endosperm development. No obvious differences in changes of the activities of AGPase and SBE between two rice cultivars investigated, except the DBEs. Distribution patterns of branches of amy- lopectin changed continually during the development of rice grains and varied between two rice culti- vars. It was suggested that amylopectin synthesis be prior to the synthesis of amylose and different enzymes have different roles in controlling syntheses of branches of amylopectin.     

FLOURY ENDOSPERM16 encoding a NAD‐dependent cytosolic malate dehydrogenase plays an important role in starch synthesis and seed development in rice

Starch is the most important form of energy storage in cereal crops. Many key enzymes involved in starch biosynthesis have been identified. However, the molecular mechanisms underlying the regulation of starch biosynthesis are largely unknown. In this study, we isolated a novel floury endosperm rice (Oryza sativa) mutant flo16 with defective starch grain (SG) formation. The amylose content and amylopectin structure were both altered in the flo16 mutant. Map‐based cloning and complementation tests demonstrated that FLO16 encodes a NAD‐dependent cytosolic malate dehydrogenase (CMDH). The ATP contents were decreased in the mutant, resulting in significant reductions in the activity of starch synthesis‐related enzymes. Our results indicated that FLO16 plays a critical role in redox homeostasis that is important for compound SG formation and subsequent starch biosynthesis in rice endosperm. Overexpression of FLO16 significantly improved grain weight, suggesting a possible application of FLO16 in rice breeding. These findings provide a novel insight into the regulation of starch synthesis and seed development in rice.     

稻米品质形成的生理基础研究进展

综述了水稻(Oryza sativa L.)米质形成的生理基础的研究进展,主要包括稻米品质形成期的源库特征、淀粉合成的关键酶以及淀粉粒的形态、结构及其糊化特性等几个内容,从植物生理学角度来揭示稻米品质形成的规律有着重要的理论意义。     

Starch metabolism in leaves

Starch is the most abundant storage carbohydrate produced in plants. The initiation of transitory starch synthesis and degradation in plastids depends mainly on diurnal cycle, post-translational regulation of enzyme activity and starch phosphorylation. For the proper structure of starch granule the activities of all starch synthase isoenzymes, branching enzymes and debranching enzymes are needed. The intensity of starch biosynthesis depends mainly on the activity of AGPase (adenosine 5'-diphosphate glucose pyrophosphorylase). The key enzymes in starch degradation are beta-amylase, isoamylase 3 and disproportionating enzyme. However, it should be underlined that there are some crucial differences in starch metabolism between heterotrophic and autotrophic tissues, e.g. is the ability to build multiprotein complexes responsible for biosynthesis and degradation of starch granules in chloroplasts. The observed huge progress in understanding of starch metabolism was possible mainly due to analyses of the complete Arabidopsis and rice genomes and of numerous mutants with altered starch metabolism in leaves. The aim of this paper is to review current knowledge on transient starch metabolism in higher plants.     

Gene expression of the biosynthetic enzymes and biosynthesis of starch during Rice Grain development

Amylose and amylopectin are determinants of the physicochemical properties for starch and grain quality in rice. Their biosynthesis is catalyzed by the interplay of ADP-glucose pyrophosphorylase (AGPase), granule-bound starch synthase (GBSS), soluble starch synthase (SSS), a starch branching enzyme (SBE), and a starch debranching enzyme (SDE). In this study, the genes for these enzymes were highly expressed 7 to 28 days after flowering during grain development, and their expression closely matched increases in both starch content and grain weight Among all the tested cultivars, amylose contents in the rice grains remained essentially constant throughout their development The AGPase gene was highly expressed in the high-yield cultivars of both glutinous and non-glutinous rice. The SSS gene was actively expressed when mature GBSS mRNA decreased. Genes responsible for amylopectin biosynthesis were simultaneously expressed in the late stage of grain development. We have now demonstrated that the expression patterns of starch biosynthetic genes differ between glutinous and non-glutinous rice, and between Tongil (a Japonica/ Indica hybrid) and Japonica types.     

Starch synthesis in the cereal endosperm

The pathway of starch synthesis in the cereal endosperm is unique, and requires enzyme isoforms that are not present in other cereal tissues or non-cereal plants. Recent information on the functions of individual enzyme isoforms has provided insight into how the linear chains and branch linkages in cereal starch are synthesized and distributed. Genetic analyses have led to the formulation of models for the roles of de-branching enzymes in cereal starch production, and reveal pleiotropic effects that suggest that certain enzymes may be physically associated. For the first time, tools for global analyses of starch biosynthesis are available for cereal crops, and are heralded by the draft sequence of the rice genome.