The SOS4 pyridoxal kinase is required for maintenance of vitamin B6-mediated processes in chloroplasts

► Vitamin B6 is required in the chloroplast for proper chloroplast function. ► Pyridoxal kinase (SOS4) is located in the chloroplast. ► Pyridoxal kinase (SOS4) functions to maintain proper vitamin B6 levels in the chloroplast. ► Our work supports a diffusion model for transport of vitamin B6 into the chloroplast.