Dissecting sequence-structure-function-diversity in plant cryptochromes

Ubiquitous to every stratum of life, cryptochromes regulate numerous light dependent functions in terrestrial plants. These include light-dependent transcription, circadian rhythm, inhibition of hypocotyl elongation, programmed cell death, promotion of floral initiation, mediation of gravitropic response, responding to biotic and abiotic stress etc. There have been quite a few seminal reviews including on plant cryptochromes, focusing mostly on the detailed functional aspects. This review primarily focuses on understanding the link connecting sequence-structure hierarchy behind the functional diversity in plant cryptochromes. With available sequence information and 3D structure data, we hereby explore the molecular origin of functional diversity in both the subtypes i.e., CRY1 and CRY2. First, we discuss the structural details and functional distinctiveness of all subtypes of plant cryptochromes. Next we draw a comparison not just between two cryptochromes but also other Cryptochrome/Photolyase Family (CPF) members e.g. CRY-DASH/CRY3 and CPD/6-4 photolyases of plant origin. Further, by constructing a phylogenetic profile from multiple sequence alignment we investigate how a crucial activity like DNA repair is restricted to some members of CPF and not all. It is a well-known fact that the function of a protein is heavily if not solely guided by the structure-sequence relationship. Therefore, the resultant hypothesis as drawn from this comparative and collective study could predict functions of many under-studied plant cryptochromes when compared with their well-studied counterparts like Arabidopsis cryptochromes. An extensive sequence-structure-function analysis complemented with evolutionary studies and bibliographic survey is useful towards understanding the immensely diverse CPF.