Division of Apple Research, Institute of Fruit Tree and Tea Science, National Agriculture and Food Research Organization, 92-24 Nabeyashiki, Shimokuriyagawa, Morioka, Iwate 020-0123, Japan.
RIKEN Center for Sustainable Resource Science, 1-7-22 Suehiro-cho, Tsurumi-ku, Yokohama, Kanagawa 230-0045, Japan.
Tree Physiol. 2020 Aug 29;40(9):1205-1216. doi: 10.1093/treephys/tpaa049.
The apple cultivar McIntosh Wijcik, which is a mutant of 'McIntosh', exhibits a columnar growth phenotype (short internodes, few lateral branches, many spurs, etc.) that is controlled by a dominant Co gene. The candidate gene (MdDOX-Co), encoding a 2-oxoglutarate-dependent dioxygenase, is located adjacent to an insertion mutation. Non-columnar apples express MdDOX-Co in the roots, whereas columnar apples express MdDOX-Co in the aerial parts as well as in the roots. However, the function of MdDOX-Co remains unknown. Here, we characterized tobacco plants overexpressing MdDOX-Co. The tobacco plants showed the typical dwarf phenotype, which was restored by application of gibberellin A3 (GA3). Moreover, the dwarf tobacco plants had low concentrations of endogenous bioactive gibberellin A1 (GA1) and gibberellin A4 (GA4). Similarly, 'McIntosh Wijcik' contained low endogenous GA4 concentration and its dwarf traits (short main shoot and internodes) were partially reversed by GA3 application. These results indicate that MdDOX-Co is associated with bioactive GA deficiency. Interestingly, GA3 application to apple trees also resulted in an increased number of lateral branches and a decrease in flower bud number, indicating that gibberellin (GA) plays important roles in regulating apple tree architecture by affecting both lateral branch formation (vegetative growth) and flower bud formation (reproductive growth). We propose that a deficiency of bioactive GA by ectopic expression of MdDOX-Co in the aerial parts of columnar apples not only induces dwarf phenotypes but also inhibits lateral branch development and promotes flower bud formation, and assembly of these multiple phenotypes constructs the columnar tree form.
麦金托什 Wijcik 苹果品种是“麦金托什”的突变体，表现出柱状生长表型（短节间、侧枝少、多枝等），由显性 Co 基因控制。候选基因（MdDOX-Co），编码一种 2-氧戊二酸依赖性双加氧酶，位于插入突变附近。非柱状苹果在根部表达 MdDOX-Co，而柱状苹果在地上部分和根部也表达 MdDOX-Co。然而，MdDOX-Co 的功能仍然未知。在这里，我们对过表达 MdDOX-Co 的烟草植物进行了表征。烟草植物表现出典型的矮化表型，用赤霉素 A3（GA3）处理可恢复。此外，矮化烟草植物内源生物活性赤霉素 A1（GA1）和赤霉素 A4（GA4）浓度较低。类似地，“麦金托什 Wijcik”含有低浓度的内源性 GA4，其矮化特性（主梢和节间短）部分被 GA3 处理逆转。这些结果表明 MdDOX-Co 与生物活性 GA 缺乏有关。有趣的是，GA3 处理苹果也导致侧枝数量增加，花蕾数量减少，表明赤霉素（GA）通过影响侧枝形成（营养生长）和花蕾形成（生殖生长）来调节苹果树结构中起着重要作用。我们提出，在柱状苹果的地上部分异位表达 MdDOX-Co 导致生物活性 GA 缺乏，不仅诱导矮化表型，还抑制侧枝发育并促进花蕾形成，这些多种表型的组合构建了柱状树型。
