Atkinson Ross G, Schröder Roswitha, Hallett Ian C, Cohen Daniel, MacRae Elspeth A
The Horticulture and Food Research Institute of New Zealand, Mount Albert Research Centre, Private Bag 92 169, Auckland, New Zealand.
Plant Physiol. 2002 May;129(1):122-33. doi: 10.1104/pp.010986.
Polygalacturonases (PGs) cleave runs of unesterified GalUA that form homogalacturonan regions along the backbone of pectin. Homogalacturonan-rich pectin is commonly found in the middle lamella region of the wall where two adjacent cells abut and its integrity is important for cell adhesion. Transgenic apple (Malus domestica Borkh. cv Royal Gala) trees were produced that contained additional copies of a fruit-specific apple PG gene under a constitutive promoter. In contrast to previous studies in transgenic tobacco (Nicotiana tabacum) where PG overexpression had no effect on the plant (K.W. Osteryoung, K. Toenjes, B. Hall, V. Winkler, A.B. Bennett [1990] Plant Cell 2: 1239-1248), PG overexpression in transgenic apple led to a range of novel phenotypes. These phenotypes included silvery colored leaves and premature leaf shedding due to reduced cell adhesion in leaf abscission zones. Mature leaves had malformed and malfunctioning stomata that perturbed water relations and contributed to a brittle leaf phenotype. Chemical and ultrastructural analyses were used to relate the phenotypic changes to pectin changes in the leaf cell walls. The modification of apple trees by a single PG gene has offered a new and unexpected perspective on the role of pectin and cell wall adhesion in leaf morphology and stomatal development.
多聚半乳糖醛酸酶（PGs）可切割未酯化的半乳糖醛酸（GalUA）链，这些链沿着果胶主链形成同型半乳糖醛酸聚糖区域。富含同型半乳糖醛酸聚糖的果胶常见于相邻两个细胞相接处的细胞壁中层区域，其完整性对于细胞黏附至关重要。培育出了转基因苹果（苹果属 家苹果品种皇家嘎啦）树，这些树在组成型启动子的控制下含有额外拷贝的果实特异性苹果PG基因。与之前在转基因烟草（烟草属 烟草）中的研究不同，在转基因烟草中PG过表达对植株没有影响（K.W. 奥斯特扬、K. 托恩耶斯、B. 霍尔、V. 温克勒、A.B. 贝内特[1990]《植物细胞》2: 1239 - 1248），而转基因苹果中PG过表达导致了一系列新的表型。这些表型包括叶片呈银色以及由于叶片脱落区细胞黏附力降低而导致的叶片过早脱落。成熟叶片的气孔畸形且功能异常，扰乱了水分关系，并导致叶片呈现脆叶表型。运用化学和超微结构分析将这些表型变化与叶细胞壁中的果胶变化联系起来。通过单个PG基因对苹果树进行改造，为果胶和细胞壁黏附在叶片形态和气孔发育中的作用提供了全新且意想不到的视角。
