Recent advancements of optogenetic systems. A–D) Recently developed new photoactivatable protein systems. E–J) Improvement of existing optogenetic systems. K–L) Existing optogenetic systems with repurposed functions. References of each photoactivatable protein are listed as follows: A) PhoCl,[10] B) PAL,[11] C) BcLOV4,[12] D) cPAC,[14] E) CRY2clust,[16] F) BphP1/Pps2,[19] G,H) FRAPA,[23] I) CcaSR v3.0,[26] J) PhyB/AtPIF,[29] K) Z-Lock,[31] and L) usage of the A’α helix of LOV.[33]