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

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 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 ; and when expressed in , increases cAMP levels . Both the AC domain and full length AtKUP5 rescue an AC-deficient mutant, , and together these data provide evidence that AtKUP5 functions as an AC. Furthermore, full length AtKUP5 complements the K transport impaired mutant, , demonstrating its function as a K transporter. Surprisingly, a point mutation in the AC center that impairs AC activity, also abolishes complementation of , 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.