Downstream Targets of Cyclic Nucleotides in Plants

Efficient integration of various external and internal signals is required to maintain adaptive cellular function. Numerous distinct signal transduction systems have evolved to allow cells to receive these inputs, to translate their codes and, subsequently, to expand and integrate their meanings. Two of these, cyclic AMP and cyclic GMP, together referred to as the cyclic nucleotide signaling system, are between them. The cyclic nucleotides regulate a vast number of processes in almost all living organisms. Once synthesized by adenylyl or guanylyl cyclases, cyclic nucleotides transduce signals by acting through a number of cellular effectors. Because the activities of several of these effectors are altered simultaneously in response to temporal changes in cyclic nucleotide levels, agents that increase cAMP/cGMP levels can trigger multiple signaling events that markedly affect numerous cellular functions. In this mini review, we summarize recent evidence supporting the existence of cNMP effectors in plant cells. Specifically, we highlight cAMP-dependent protein kinase A (PKA), cGMP-dependent kinase G (PKG), and cyclic nucleotide phosphodiesterases (PDEs). Essentially this manuscript documents the progress that has been achieved in recent decades in improving our understanding of the regulation and function of cNMPs in plants and emphasizes the current gaps and unanswered questions in this field of plant signaling research

Plant effectors of cyclic nucleotides

Mechanizmy, za pomocą których sygnały wewnątrz- i zewnątrzkomórkowe wywołują specyficzną odpowiedź biologiczną są istotne dla regulacji funkcji komórek, procesów wzrostu i rozwoju oraz odpowiedzi na zmiany środowiska. W ostatnich latach dokonał się ogromny postęp w badaniu elementów zaangażowanych w regulację procesów zachodzących w komórkach roślinnych o czym świadczy olbrzymia ilość publikacji poruszających problem sygnalizacji komórkowej. Cykliczne nukleotydy (cNMP) są cząsteczkami sygnalnymi, których obecność i zaangażowanie w szereg procesów w komórkach roślinnych nie budzą już wątpliwości. Z fizjologicznego punktu widzenia, stężenie cNMP w miejscu ich działania nie może być ani za wysokie ani za niskie, a jest to normowane przez odpowiednie układy generujące i inaktywujące cykliczne nukleotydy. Ponadto na końcowy efekt biologiczny ma wpływ sprawność systemów efektorowych wrażliwych na zmiany stężenia cyklicznych nukleotydów takich jak fosfodiesterazy, kinazy regulowane lub zależne od cNMP i kanały bramkowane cyklicznymi nukleotydami. W pracy tej podsumowano aktualną wiedzę dotyczącą efektorów cyklicznych nukleotydów, skupiając się zarówno na ich budowie, jak i aspekcie ich funkcjonowania w komórkach roślinnych.The mechanisms by which intra- and extracellular signals induce a specific biological response are important for the regulation of cell function, processes of growth and development and responses to environmental changes. In recent years, enormous progress has been made in studies of elements involved in the regulation of processes occurring in plant cells. Cyclic nucleotides (cNMP) are signaling molecules whose presence and involvement in a number of processes in plant cells is well documented. From the physiological point of view, the concentration of cNMP's at a site of their action could be neither too high nor too low, as it is controlled by the systems that lead to their synthesis or inactivation. In addition, the final biological effect depends on the efficiency of the effector systems such as cyclic nucleotide phosphodiesterases, cNMP-dependent or cNMP-regulated protein kinase and cyclic-nucleotide gated channels, that are sensitive to changes in cNMP concentration. In this paper we summarize the current knowledge on the cyclic nucleotide effectors, focusing both on their structure and functioning in plant cells

BdGUCD1 and Cyclic GMP Are Required for Responses of Brachypodium distachyon to Fusarium pseudograminearum in the Mechanism Involving Jasmonate

Guanosine 3′,5′-cyclic monophosphate (cGMP) is an important signaling molecule in plants. cGMP and guanylyl cyclases (GCs), enzymes that catalyze the synthesis of cGMP from GTP, are involved in several physiological processes and responses to environmental factors, including pathogen infections. Using in vitro analysis, we demonstrated that recombinant BdGUCD1 is a protein with high guanylyl cyclase activity and lower adenylyl cyclase activity. In Brachypodium distachyon, infection by Fusarium pseudograminearum leads to changes in BdGUCD1 mRNA levels, as well as differences in endogenous cGMP levels. These observed changes may be related to alarm reactions induced by pathogen infection. As fluctuations in stress phytohormones after infection have been previously described, we performed experiments to determine the relationship between cyclic nucleotides and phytohormones. The results revealed that inhibition of cellular cGMP changes disrupts stress phytohormone content and responses to pathogen. The observations made here allow us to conclude that cGMP is an important element involved in the processes triggered as a result of infection and changes in its levels affect jasmonic acid. Therefore, stimuli-induced transient elevation of cGMP in plants may play beneficial roles in priming an optimized response, likely by triggering the mechanisms of feedback control

In Vitro Characterization of Guanylyl Cyclase BdPepR2 from Brachypodium distachyon Identified through a Motif-Based Approach

In recent years, cyclic guanosine 3′,5′-cyclic monophosphate (cGMP) and guanylyl cyclases (GCs), which catalyze the formation of cGMP, were implicated in a growing number of plant processes, including plant growth and development and the responses to various stresses. To identify novel GCs in plants, an amino acid sequence of a catalytic motif with a conserved core was designed through bioinformatic analysis. In this report, we describe the performed analyses and consider the changes caused by the introduced modification within the GC catalytic motif, which eventually led to the description of a plasma membrane receptor of peptide signaling molecules—BdPepR2 in Brachypodium distachyon. Both in vitro GC activity studies and structural and docking analyses demonstrated that the protein could act as a GC and contains a highly conserved 14-aa GC catalytic center. However, we observed that in the case of BdPepR2, this catalytic center is altered where a methionine instead of the conserved lysine or arginine residues at position 14 of the motif, conferring higher catalytic activity than arginine and alanine, as confirmed through mutagenesis studies. This leads us to propose the expansion of the GC motif to cater for the identification of GCs in monocots. Additionally, we show that BdPepR2 also has in vitro kinase activity, which is modulated by cGMP