College of Horticulture, Northwest A&F University, Taicheng Road No.3, Xianyang 712100, China.
Int J Mol Sci. 2022 Aug 4;23(15):8699. doi: 10.3390/ijms23158699.
Dwarfing is an important agronomic characteristic in fruit breeding. However, due to the lack of dwarf cultivars and dwarf stocks, the dwarfing mechanism is poorly understood in pears. In this research, we discovered that the dwarf hybrid seedlings of pear ( Rehd.), 'Red Zaosu,' exhibited a xylem-deficient dwarf phenotype. The expression level of , a suppressor of xylem development, was markedly enhanced in dwarf hybrid seedlings and its overexpression in pear results in a xylem-deficient dwarf phenotype. To further dissect the mechanism of PbXND1, PbTCP4 was isolated as a PbXND1 interaction protein through the pear yeast library. Root transformation experiments showed that PbTCP4 promotes root xylem development. Dual-luciferase assays showed that PbXND1 interactions with PbTCP4 suppressed the function of PbTCP4. PbXND1 expression resulted in a small amount of PbTCP4 sequestration in the cytoplasm and thereby prevented it from activating the gene expression, as assessed by bimolecular fluorescence complementation and co-location analyses. Additionally, PbXND1 affected the DNA-binding ability of PbTCP4, as determined by utilizing an electrophoretic mobility shift assay. These results suggest that PbXND1 regulates the function of PbTCP4 principally by affecting the DNA-binding ability of PbTCP4, whereas the cytoplasmic sequestration of PbTCP4 is only a minor factor. Taken together, this study provides new theoretical support for the extreme dwarfism associated with the absence of xylem caused by PbXND1, and it has significant reference value for the breeding of dwarf varieties and dwarf rootstocks of the pear.
矮化是果树育种中的一个重要农艺性状。然而，由于缺乏矮化品种和矮化砧木，梨的矮化机制还不清楚。本研究发现，梨（Rehd.）矮化杂交实生苗‘红早酥’表现出木质部缺陷型矮化表型。在矮化杂交实生苗中，抑制木质部发育的 基因表达水平显著增强，其在梨中的过表达导致木质部缺陷型矮化表型。为了进一步剖析 PbXND1 的作用机制，通过梨酵母文库分离到其互作蛋白 PbTCP4。根转化实验表明 PbTCP4 促进根木质部发育。双荧光素酶报告基因实验表明 PbXND1 与 PbTCP4 互作抑制 PbTCP4 的功能。PbXND1 表达导致细胞质中 PbTCP4 大量被隔离，从而阻止其激活基因表达，这可通过双分子荧光互补和共定位分析来评估。此外，PbXND1 影响 PbTCP4 的 DNA 结合能力，这可通过电泳迁移率变动分析来确定。这些结果表明，PbXND1 主要通过影响 PbTCP4 的 DNA 结合能力来调节其功能，而 PbTCP4 的细胞质隔离只是一个次要因素。综上所述，本研究为 PbXND1 引起的木质部缺失导致的极端矮化提供了新的理论支持，对梨矮化品种和矮化砧木的选育具有重要的参考价值。
