The Arabidopsis thaliana K+-Uptake Permease 5 (AtKUP5) Contains a Functional Cytosolic Adenylate Cyclase Essential for K+ Transport

Abstract
Potassium (K+) is the most abundant cation in plants, and its uptake and transport are key to growth, development and responses to the environment. Here, we report that Arabidopsis thaliana K+ uptake permease 5 (AtKUP5) contains an adenylate cyclase (AC) catalytic center embedded in its N-terminal cytosolic domain. The purified recombinant AC domain generates cAMP in vitro; and when expressed in Escherichia coli, increases cAMP levels in vivo. Both the AC domain and full length AtKUP5 rescue an AC-deficient E. coli mutant, cyaA, and together these data provide evidence that AtKUP5 functions as an AC. Furthermore, full length AtKUP5 complements the Saccharomyces cerevisiae K+ transport impaired mutant, trk1 trk2, demonstrating its function as a K+ transporter. Surprisingly, a point mutation in the AC center that impairs AC activity, also abolishes complementation of trk1 trk2, suggesting that a functional catalytic AC domain is essential for K+ uptake. AtKUP5-mediated K+ uptake is not affected by cAMP, the catalytic product of the AC, but, interestingly, causes cytosolic cAMP accumulation. These findings are consistent with a role for AtKUP5 as K+ flux sensor, where the flux-dependent cAMP increases modulate downstream components essential for K+ homeostasis, such as cyclic nucleotide gated channels.

Citation
Al-Younis I, Wong A, Lemtiri-Chlieh F, Schmöckel S, Tester M, et al. (2018) The Arabidopsis thaliana K+-Uptake Permease 5 (AtKUP5) Contains a Functional Cytosolic Adenylate Cyclase Essential for K+ Transport. Frontiers in Plant Science 9. Available: http://dx.doi.org/10.3389/fpls.2018.01645.

Acknowledgements
This project was funded by King Abdullah University of Science and Technology. AW was supported by National Natural Science Foundation of China (Grant No. 31850410470) and Zhejiang Provincial Natural Science Foundation of China (Grant No. Q19C130001). LD was supported by the National Research Foundation (Grant Nos. 91453 and 106972).

Publisher
Frontiers Media SA

Journal
Frontiers in Plant Science

DOI
10.3389/fpls.2018.01645

Additional Links
https://www.frontiersin.org/articles/10.3389/fpls.2018.01645

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