Abstract
Dwarf cultivars or dwarfing rootstocks enable high-density planting and are therefore highly desirable in modern pear production. Previously, we found that the dwarf growth habit of pear is controlled by a single dominant gene PcDw. In this study, PcPIN-L (PCP021016) was cloned from dwarf-type and standard-type pears. PcPIN-L expression was significantly lower in the dwarf-type pears than in standard-type pears, which was caused by the CT repeat deletion in the promoter of dwarf-type pears. PcPIN-L overexpression in tobacco plants enhanced the growth of the stems and the roots. Notably, the indole acetic acid (IAA) content decreased in the shoot tips and increased in the stems of transgenic lines compared with wild type, which is consistent with the greater IAA content in the shoot tips and lower IAA content in the stems of dwarf-type pears than in standard-type pears. The CT repeat deletion in the promoter that causes a decrease in promoter activity is associated with lower PcPIN-L expression in the dwarf-type pears, which might limit the polar auxin transport and in turn result in the dwarf phenotype. Taken together, the results provide a novel dwarfing molecular mechanism in perennial woody plants.
Highlights
Dwarfing and high-density planting are important developments in the cultivation and production of modern fruit orchards for higher yield per hectare and efficient mechanised management[1,2]
To determine the similarity of the PcPIN-L sequence in relation to the PINs of Arabidopsis thaliana, Malus domestica[45], and Populus trichocarpa[46], a phylogenetic tree based on the amino acid sequences of PIN family was constructed using MEGA 5.2 software
The results showed that the PcPIN-L was most closely related to MdPIN4, MdPIN7a and MdPIN7b of Malus domestica, PtrPIN3a and PtrPIN3b of Populus trichocarpa, AtPIN3, AtPIN7 and AtPIN4 of Arabidopsis thaliana (Fig. 1)
Summary
Dwarfing and high-density planting are important developments in the cultivation and production of modern fruit orchards for higher yield per hectare and efficient mechanised management[1,2]. The dwarf phenotype resulted from the changes in both cell division and cell elongation, which are regulated by endogenous cytokinin (CTK), gibberellin, auxin (indole acetic acid, IAA), abscisic acid and brassinosteroid[13,14,15,16] Amongst these crucial plant hormones, IAA is considered to be one of the most important hormones in the dwarfism mechanism. IAA is synthesised in the apical meristem and transported downward to the root tips through the cambium and phloem This is essential for regulating the plant growth and development[17,18]. The findings of this study will clarify the role of PIN-dependent auxin polar transports in the dwarfing mechanism of pear trees and will contribute to the molecular breeding of dwarf pear cultivars, which is crucial for modern pear production
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