Nitric oxide (NO) is a fast-diffusible gas that acts as a key signalling molecule in multiple developmental and physiological settings in both animals and plants. One such setting is plant sexual reproduction, where NO regulates pollen-stigma interaction and pollen tube (PT) guidance; however, which proteins are involved in mediating this NO response had yet to be discovered. Now, the teams of José Feijó and Chris Gehring join forces to show that Arabidopsis DIACYLGLYCEROL KINASE4 (DGK4) is involved in pollen NO signalling. In vitro, DGK4 mutant PTs grow slowly, and their growth rate and direction is relatively insensitive to NO; similarly, in vivo, mutant PTs grow more slowly and were outcompeted by wild-type PTs. Sequence analysis reveals that DGK4 contains an H-NOX-like signature known to mediate NO sensing in other organisms. DGK4 protein shows spectral and catalytic changes which are compatible with a role in NO perception and signalling, and DGK4 displays both kinase activity and guanylyl cyclase activity. Both cGMP and NO inhibit the kinase activity, but NO did not inhibit the guanylyl cyclase activity. This work therefore implicates DGK4 as a key mediator in NO sensing and signalling during plant reproduction.
