Transfer of cyclobutane pyrimidine dimer photolyase to chloroplasts for Poaceae survival under ultraviolet-B radiation

Cyclobutane pyrimidine dimer (CPD) photolyase (PHR), the primary enzyme for repairing the CPD induced by ultraviolet B (UV-B) radiation, is essential for plants living under sunlight. Rice CPD photolyase (OsPHR), is such a unique triple-targeting protein. The signal sequences required for its translocation to the nucleus or mitochondria are located in the C-terminal region but were yet to be identified for chloroplasts. Here, we identified sequences located in the N-terminal region, including the serine-phosphorylation site at position 7 of OsPHR, and found that OsPHR is transported/localized to chloroplasts via a vesicle transport system under the control of serine phosphorylation. However, the sequence identified in this study is only conserved in some Poaceae species and in many other plants, PHR does not localize to chloroplasts Therefore, we reasoned that Poaceae species need the ability to repair CPD in the chloroplast genome to survive under sunlight and have acquired this new mechanism for chloroplast translocation.