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MdPIN1b encodes a putative auxin efflux carrier and has different expression patterns in BC and M9 apple rootstocks

Authors
  • Gan, Zengyu1, 2, 3
  • Wang, Yi1, 2, 3
  • Wu, Ting1, 2, 3
  • Xu, Xuefeng1, 2, 3
  • Zhang, Xinzhong1, 2, 3
  • Han, Zhenhai1, 2, 3
  • 1 China Agricultural University, Institute of Horticultural Plants, College of Horticulture, Beijing, 100193, People’s Republic of China , Beijing (China)
  • 2 China Agricultural University, Key Laboratory of Stress Physiology and Molecular Biology for Fruit Trees in Beijing Municipality, Beijing, 100193, People’s Republic of China , Beijing (China)
  • 3 China Agricultural University, Key Laboratory of Biology and Genetic Improvement of Horticultural Crops (Nutrition and Physiology) in Ministry of Agriculture, Beijing, 100193, People’s Republic of China , Beijing (China)
Type
Published Article
Journal
Plant Molecular Biology
Publisher
Springer Netherlands
Publication Date
Jan 17, 2018
Volume
96
Issue
4-5
Pages
353–365
Identifiers
DOI: 10.1007/s11103-018-0700-6
Source
Springer Nature
Keywords
License
Yellow

Abstract

Key messageLower promoter activity is closely associated with lower MdPIN1b expression in the M9 interstem, which might contribute to the dwarfing effect in apple trees.AbstractApple trees grafted onto dwarfing rootstock Malling 9 (M9) produce dwarfing tree architecture with high yield and widely applying in production. Previously, we have reported that in Malus ‘Red Fuji’ (RF) trees growing on M9 interstem and Baleng Crab (BC) rootstock, IAA content was relatively higher in bark tissue of M9 interstem than that in scion or rootstock. As IAA polar transportation largely depends on the PIN-FORMED (PIN) auxin efflux carrier. Herein, we identify two putative auxin efflux carrier genes in Malus genus, MdPIN1a and MdPIN1b, which were closely related to the AtPIN1. We found that MdPIN1b was expressed preferentially in BC and M9, and the expression of MdPIN1b was significantly lower in the phloem of M9 interstem than that in the scion and rootstock. The distinct expression of MdPIN1b and IAA content were concentrated in the cambium and adjacent xylem or phloem, and MdPIN1b protein was localized on cell plasma membrane in onion epidermal cells transiently expressing 35S:MdPIN1b-GFP fusion protein. Interestingly, an MdPIN1b mutant allele in the promoter region upstream of M9 exhibited decreased MdPIN1b expression compared to BC. MdPIN1b over-expressing interstem in tobacco exhibited increased polar auxin transport. It is proposed that natural allelic differences decreased promoter activity is closely associated with lower MdPIN1b expression in the M9 interstem, which might limit the basipetal transport of auxin, and in turn might contribute to the dwarfing effect. Taken together, these results reveal allelic variation underlying an important apple rootstock trait, and specifically a novel molecular genetic mechanism underlying dwarfing mechanism.

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