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Article|11 Apr 2022|OPEN
MYB308-mediated transcriptional activation of plasma membrane H+-ATPase 6 promotes iron uptake in citrus 
Zhengyan Fan1 , Yifang Wu1 , Liuying Zhao1 , Lina Fu1 , Lile Deng1,2 , Dekuan Ding2 , Shunyuan Xiao3 , Xiuxin Deng1 and Shu’ang Peng1 , , Zhiyong Pan,1
1Key Laboratory of Horticultural Plant Biology (Ministry of Education), Key Laboratory of Horticultural Crop Biology and Genetic Improvement (Central Region, Ministry of Agriculture), College of Horticulture and Forestry Sciences, Huazhong Agricultural University, Wuhan 430070, China
2Chenggu Fruit Industry Technical Guidance Station, Shaanxi 723200, China
3Institute for Bioscience and Biotechnology Research & Department of Plant Sciences and Landscape Architecture, University of Maryland College Park, Rockville, MD 20850, USA
*Corresponding author. E-mail: zypan@mail.hzau.edu.cn

Horticulture Research 9,
Article number: uhac088 (2022)
doi: https://doi.org/10.1093/hr/uhac088
Views: 19

Received: 29 Dec 2021
Accepted: 30 Mar 2022
Published online: 11 Apr 2022

Abstract

Iron-deficiency chlorosis is a common nutritional disorder in crops grown on alkaline or calcareous soils. Although the acclimation mechanism to iron deficiency has been investigated, the genetic regulation of iron acquisition is still unclear. Here, by comparing the iron uptake process between the iron-poor-soil-tolerant citrus species Zhique (ZQ) and the iron-poor-soil-sensitive citrus species trifoliate orange (TO), we discovered that enhanced root H + efflux is crucial for the tolerance to iron deficiency in ZQ. The H+ efflux is mainly regulated by a plasma membrane-localized H+-ATPase, HA6, the expression of which is upregulated in plants grown in soil with low iron content, and significantly higher in the roots of ZQ than TO. Overexpression of the HA6 gene in the Arabidopsis thaliana aha2 mutant, defective in iron uptake, recovered the wild-type phenotype. In parallel, overexpression of the HA6 gene in TO significantly increased iron content of plants. Moreover, an iron deficiency-induced transcription factor, MYB308, was revealed to bind the promoter and activate the expression of HA6 in ZQ in yeast one-hybrid, electrophoretic mobility shift, and dual-luciferase assays. Overexpression of MYB308 in ZQ roots significantly increased the expression level of the HA6 gene. However, MYB308 cannot bind or activate the HA6 promoter in TO due to the sequence variation of the corresponding MYB308 binding motif. Taking these results together, we propose that the MYB308 could activate HA6 to promote root H+ efflux and iron uptake, and that the distinctive MYB308-HA6 transcriptional module may be, at least in part, responsible for the iron deficiency tolerance in citrus.