Structural And Functional Analysis of CCT Family Genes In Pigeonpea

Abstract

Pigeonpea (Cajanus cajan (L) Millsp) is a short-day plant in which the flowering is highly sensitive to photoperiod. A better understanding of the genes modulating photoresponse and flowering time is critical to developing photoperiod insensitive pigeonpea cultivars for cultivation across the seasons. We identified 33 CCT family genes (CcCCT1- CcCCT33) in C. cajan and localized them on 10 chromosomes and nine genomic scaffolds. The structural analysis of CCT family genes revealed a considerable variation in length and distribution of exons and introns. Based on the type of domain(s), we classified the CCT family genes into CCT motif family (CMF) type, CONSTANS like (COL) type, Pseudo-response Regulator (PRR) type, and GATA and tifi containing CCT (GTCC) type. The CCT family genes of C. cajan exhibited an extensive orthologous relationship with the CCT family genes of other legume species. We also observed significant sharing of CCT family genes among the legume species. Glycine max exhibited the maximum sharing of CCT family genes with C. cajan. The analysis of CCT family proteins-based phylogenic relationships revealed a general congruence with the legumes' taxonomic relationships. The expression analysis of CCT family genes of pigeonpea demonstrated that CcCCT4 and CcCCT23 are the active CONSTANS (CO) in ICP20338. In contrast, only CcCCT23 is active in MAL3, explaining the differential response of ICP20338 and MAL3 to photoperiod. The chromosomes of C. cajan contain a variable number of CCT family genes. A majority of these genes are localized in the centromeric regions. The COL type CCT genes are structurally highly diverse and contain a variable number of B-box domains. The CCT family genes of different legume species exhibit all three kinds of relationships: one-to-one, many-to-one, and many-to-many types. The photoperiod insensitive cultivar ICP20338 contains CcCCT4 and CcCCT23, while the photoperiod sensitive cultivar MAL3 contains only CcCCT23 as active CONSTANS (CO), which may be the plausible reason for their differential photoperiod response.