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Article|13 Dec 2017|OPEN
Endogenous auxin and its manipulation influence in vitro shoot organogenesis of citrus epicotyl explants
Wei Hu1,2,4, Xiaomin Wang3,2, Sabrina Fagundez4,2, Lorenzo Katin-Grazzi2, Yanjun Li2, Wei Li2, Yingnan Chen2, Shenxi Xie1, Richard J McAvoy2, Yi Li2,1, & Ziniu Deng1,
1National Center for Citrus Improvement, Horticulture and Landscape College, Hunan Agricultural University, Changsha 410128, People’s Republic of China
2Department of Plant Science and Landscape Architecture, University of Connecticut, Storrs, CT 06269, USA
3Institute of Botany, Jiangsu Province and Chinese Academy of Sciences, 210014 Nanjing, People’s Republic of China.
4These authors contributed equally to this work.

Horticulture Research 4,
Article number: 17071 (2017)
doi: 10.1038/hortres.2017.71
Views: 937

Received: 28 Oct 2017
Revised: 13 Nov 2017
Accepted: 13 Nov 2017
Published online: 13 Dec 2017


Endogenous auxin is an important regulator of in vivo organ development, but its role in in vitro organogenesis is unclear. It has been observed that the basal end of epicotyl cuttings of juvenile citrus seedlings produces fewer shoots than the apical end. Here, we report that elevated endogenous auxin levels in the basal end of citrus epicotyl cuttings are inhibitory for in vitro shoot organogenesis. Using transgenic citrus plants expressing an auxin-inducible GUS reporter gene, we have observed elevated levels of auxin at the basal end of stem cuttings that are mediated by polar auxin transport. Depleting endogenous auxin or blocking polar auxin transport enhances shoot organogenesis. An auxin transport inhibitor, N-1-naphthylphthalamic acid (NPA), can also enhance shoot organogenesis independent of its action on polar auxin transport. Finally, we demonstrate that the promotional effects of depleting endogenous auxin or blocking polar auxin transport on shoot organogenesis are cytokinin-dependent. Our study thus provides meaningful insights into possible roles of endogenous auxin and polar auxin transport, as well as auxin–cytokinin interactions, in in vitro shoot organogenesis. Meanwhile, our results may also provide practical strategies for improving in vitro shoot organogenesis for citrus and many other plant species.