Molecular genetic on the storage capability and preharvest dropness of apple fruit

苹果（Malus × domestica Borkh.）果实成熟的开始是由催熟激素乙烯的产生引起的。果实产生乙烯的数量取决于成熟特异性的1-氨基环丙烷-1-羧酸（ACC）合成酶基因的转录水平。我们发现一个等位基因（MdACS1-2）在5'侧区含有插入的反转录子样序列，其转录水平低于野生型（MdACS1-1）。MdACS1-2/2纯合子果实在更年期产生的乙烯含量低于野生型果实。我们还发现MdACS1-2/2果树的苹果品种和品系的采前落果率低于MdACS1-1/1或MdACS1-1/2果树。用乙烯受体阻滞剂1-MCP处理MdACS1-2/2树进一步降低了落果率。分析商品苹果品种MdACS1-2/2等位基因的存在，有助于对低落果率的苹果品种进行早期检测。从苹果（Malus × domestica Borkh.）培养苗（MdExp1）、成熟果实果肉（MdExp2、MdExp3、MdExp4）和果蒂组织（MdExp5、MdExp6）中分离到6个编码扩增蛋白的cdna。本文报道了这些MdExp基因在果实发生过程中的表达特征。MdExp1在盛花期至成熟前呈上升-下降-上升周期表达。MdExp2和MdExp5的表达是在细胞增殖期后开始细胞扩增时开始的；MdExp5的表达仅限于快速生长期早期。MdExp3和MdExp4的转录本在两个生长阶段都存在上升-下降-上升的循环，但MdExp3的表达在成熟期增加。MdExp6的转录本在任何生长阶段均未检测到，但受到损伤诱导。这些结果表明，苹果果实在个体发育过程中至少需要5个扩张蛋白基因，而MdExp3是一个成熟相关的扩张蛋白基因。少

The onset of apple (Malus × domestica Borkh.) fruit maturity is preceded by the production of ethylene, the ripening hormone, which induces fruit ripening. The amount of ethylene produced by the fruits depends on the level of transcription of the ripening-specific 1-aminocycloropropane-1-carboxylate (ACC) synthase genes. We have found that an allele (MdACS1-2) which contains an inserted retroposon-like sequence at the 5'-flanking region is transcribed at a lower level than the wild-type (MdACS1-1). MdACS1-2/2 homozygous fruits produce a lower level of ethylene at the climacteric stage than does the wild type fruit. We have also found that the preharvest drop rates of apple cultivars and strains of MdACS1-2/2 trees have less fruit drop than the MdACS1-1/1 or MdACS1-1/2 trees. Treatment of the MdACS1-2/2 trees with 1-MCP, an ethylene receptor blocker, further decreased fruit drop. Analysis of commercial apple cultivars for the presence of the MdACS1-2/2 allele may help in the early detec … More tion of apple cultivars with a low fruit drop rate.Six cDNAs encoding expansins were isolated from cultured shoots (MdExp1), the flesh of ripening fruit (MdExp2, MdExp3, MdExp4), and fruit pedicel tissue (MdExp5, MdExp6) of apple (Malus × domestica Borkh.). We report here the expression characteristics of these MdExp genes during fruit ontogeny. MdExp1 was expressed in an up-down-up cycle from full-bloom stage to just before ripening. The expression of MdExp2 and MdExp5 was initiated when cell expansion was started after the cell proliferation stage; the expression of MdExp5 was limited to the early rapid growth period. The up-down-up cycles were also detected in the transcripts of MdExp3 and MdExp4 throughout both growth stages, but the expression of MdExp3 was increased in the ripening stage. Transcripts of MdExp6 were not detected in any growth stage, but were induced by wounding. These results suggest that apple fruit requires at least five expansin genes during ontogeny, and that MdExp3 is a ripening-related expansin gene. Less