Pyr-miR171f-targeted PyrSCL6 and PyrSCL22 genes regulate shoot growth by responding to IAA signaling in pear

Abstract

MicroRNA171 (miR171) is a highly conserved miRNA family, crucial for plant growth and development, and has been reported in Arabidopsis thaliana and tomato (Solanum lycopersicum), but the role of miR171 has not been explored in pear. In this study, an effort was made to decipher the mechanism underlying dwarf in ‘Zhongai 3’, of which the shoot length and shoot growth rate during the growing season were much less than those of the vigorous cultivar ‘Zaosu’, and the same for the indole-3-acetic acid (IAA) content in shoot tips after May 22, 2016. We identified a member of the miR171 family, which was most sensitive to IAA and targeted two genes conformed by 5′-RACE, and we named Pyr-miR171f. The two targets were named as PyrSCL6 and PyrSCL22, and contained a GRAS-conserved domain and encoded nucleus proteins. Quantitative RT-PCR analysis revealed that Pyr-miR171f was more abundant in ‘Zaosu’ shoot tips than in ‘Zhongai 3’ shoot tips, whereas the PyrSCL6 and PyrSCL22 mRNAs were more abundant in ‘Zhongai 3’ shoot tips than in ‘Zaosu’ shoot tips. The abundance of Pyr-miR171f and PyrSCL6 and PyrSCL22 mRNAs increased, but the trends were opposite between Pyr-miR171f and its target mRNAs in tissue culture seedlings treated by IAA. Our results suggest that IAA-induced miR171f negatively regulates the IAA signaling cascade via the GRAS pathway to maintain apical dominance. This work reveals a role for the miR171-SCL pathway in the dwarfing of ‘Zhongai 3’, and provides a theoretical basis for dwarf pear breeding.