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

苹果(Malus×home tica Borkh.)果实成熟之前会产生乙烯，这是一种促使果实成熟的成熟荷尔蒙。果实产生的乙烯量取决于成熟特有的1-氨基环丙烷-1-羧酸(ACC)合成酶基因的转录水平。我们发现，在5‘侧翼区插入反转录病毒类似序列的等位基因(MdACS1-2)的转录水平低于野生型(MdACS1-1)。MdACS1-2/2纯合子果实在跃变期产生的乙烯水平低于野生型果实。我们还发现，苹果品种和品系MdACS1-2/2的采前落果率低于MdACS1-1/1或MdACS1-1/2。用乙烯受体阻断剂1-MCP处理MdACS1-2/2，可进一步减少落果。分析商品苹果品种中是否存在MDACS1-2/2等位基因可能有助于早期检测…从苹果试管苗(MdExp1)、成熟果肉(MdExp2、MdExp3、MdExp4)和果梗组织(MdExp5、MdExp6)中分离到6个扩展蛋白基因。我们报道了这些MdExp基因在果实个体发育过程中的表达特征。MdExp1在盛花期至成熟前的表达呈上升-下降-上升的循环。MdExp2和MdExp5的表达始于细胞增殖期后的细胞扩增，MdExp5的表达仅限于细胞快速生长早期。在MdExp3和MdExp4的转录产物中，MdExp3和MdExp4的表达在两个生长阶段都有明显的上升-下降-上升周期，但在成熟期MdExp3的表达有所增加。MdExp6的转录本在各生长阶段均未检测到，但受创伤诱导。这些结果表明，苹果果实在个体发育过程中至少需要5个Expansin基因，MdExp3是一个与成熟相关的Expansin基因。较少

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