Journal
PLANT AND CELL PHYSIOLOGY
Volume 57, Issue 10, Pages 2194-2201Publisher
OXFORD UNIV PRESS
DOI: 10.1093/pcp/pcw136
Keywords
Arabidopsis thaliana; Auxin; AUX1; Phosphorylation; PM H+-ATPase; Root
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Funding
- Ministry of Education, Culture, Sports, Science, and Technology, Japan [22119005, 15H05956, 15H04386]
- Japan Society for the Promotion of Science [10J00254, 25840105]
- Grants-in-Aid for Scientific Research [10J00254, 15H05956, 15K07101, 15H04386, 25840105, 22119005] Funding Source: KAKEN
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The plant plasma membrane (PM) H+-ATPase regulates pH homeostasis and cell elongation in roots through the formation of an electrochemical H+ gradient across the PM and a decrease in apoplastic pH; however, the detailed signaling for the regulation of PM H+-ATPases remains unclear. Here, we show that an auxin influx carrier, AUXIN RESISTANT1 (AUX1), is required for the maintenance of PM H+-ATPase activity and proper root elongation. We isolated a low pH-hypersensitive 1 (loph1) mutant by a genetic screen of Arabidopsis thaliana on low pH agar plates. The loph1 mutant is a loss-of-function mutant of the AUX1 gene and exhibits a root growth retardation restricted to the low pH condition. The ATP hydrolysis and H+ extrusion activities of the PM H+-ATPase were reduced in loph1 roots. Furthermore, the phosphorylation of the penultimate threonine of the PM H+-ATPase was reduced in loph1 roots under both normal and low pH conditions without reduction of the amount of PM H+-ATPase. Expression of the DR5: GUS reporter gene and auxin-responsive genes suggested that endogenous auxin levels were lower in loph1 roots than in the wild type. The aux1-7 mutant roots also exhibited root growth retardation in the low pH condition like the loph1 roots. These results indicate that AUX1 positively regulates the PM H+-ATPase activity through maintenance of the auxin accumulation in root tips, and this process may serve to maintain root elongation especially under low pH conditions.
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