Abstract
In plants, rapid and reversible biological responses to environmental cues may require complex cellular reprograming. This is enabled by signaling molecules such as the cyclic nucleotide monophosphates (cNMPs) cAMP and cGMP, as well as Ca2+. While the roles and synthesis of cAMP and cGMP in plants are increasingly well-characterized, the “off signal” afforded by cNMP-degrading enzymes, the phosphodiesterases (PDEs), is, however, poorly understood, particularly so in monocots. Here, we identified a candidate PDE from the monocot Brachypodium distachyon (BDPDE1) and showed that it can hydrolyze cNMPs to 5′NMPs but with a preference for cAMP over cGMP in vitro. Notably, the PDE activity was significantly enhanced by Ca2+ only in the presence of calmodulin (CaM), which interacts with BDPDE1, most likely at a predicted CaM-binding site. Finally, based on our biochemical, mutagenesis and structural analyses, we constructed a comprehensive amino acid consensus sequence extracted from the catalytic centers of annotated and/or experimentally validated PDEs across species to enable a broad application of this search motif for the identification of similar active sites in eukaryotes and prokaryotes.
Highlights
Introduction published maps and institutional affilCyclic nucleotide monophosphates, such as 30,50 -cyclic adenosine monophosphate and 30,50 -cyclic guanosine monophosphate, are well-established as essential signaling and effector molecules in both prokaryotes and eukaryotes [1,2]
We set out to discover the as yet elusive monocot phosphodiesterases that are key to the regulation of the cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP) levels in the cell
Motif, which is shared with the family of metal hydrolases and class I PDEs; proteins referred to as YpgQ hydrolases can function as putative phosphodiesterases. This is consistent with the fact that ATCN-PDE1, which participates in the opening of stomata in response to UVA, reduces the pool of cGMP [16]
Summary
Cyclic nucleotide monophosphates (cNMPs), such as 30 ,50 -cyclic adenosine monophosphate (cAMP) and 30 ,50 -cyclic guanosine monophosphate (cGMP), are well-established as essential signaling and effector molecules in both prokaryotes and eukaryotes [1,2]. Recent evidence has established cNMP-dependent processes in plants ranging from signaling to the control of transcription, translation and metabolism [4,5,6,7,8]. The cyclic NMP levels are dependent on the activities of two key enzymes, the cyclic mononucleotide cyclases and cyclic mononucleotide phosphodiesterases (PDEs). Adenylyl (AC) and guanylyl (GC) cyclases catalyze the conversions of ATP and GTP to the respective products cAMP and cGMP. Cyclic AMP and cGMP, in turn, serve as “on signals” for cNMPdependent cellular processes.
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