TABLE 1.

New frontiers in c-di-GMP signaling

New Frontier	Rationale
Identifying environmental signals that control c-di-GMP	Only a handful of environmental signals that control c-di-GMP synthesis or degradation have been identified, despite the fact that thousands of DGCs and PDEs are present in bacterial genomes.
Understanding c-di-GMP in other bacteria	C-di-GMP is widespread and remains to be intensively studied in many bacteria, including the Gram-positives
Elucidating c-di-GMP controlled phenotypes	The last few years have revealed many new phenotypes controlled by c-di-GMP. What other behaviors are impacted by c-di-GMP?
Discovering c-di-GMP effectors	Although a number of c-di-GMP binding effectors have been identified, it is my opinion that we have just found the tip of the iceberg.
Determining signaling specificity	Does c-di-GMP function via low- or high-specificity signaling pathways, or a mixture of both? What are the molecular mechanisms that maintain segregation of c-di-GMP in the cell?
Development of a single-cell c-di-GMP sensor	Additional biosensors to quantify c-di-GMP at single-cell resolution need to be developed to allow examination of this signal in challenging environments such as in vivo infection.
Targeting c-di-GMP	Disrupting c-di-GMP signaling is an attractive strategy to treat biofilm-based infections.