Characterization and analysis of the promoter region of monodehydroascorbate reductase 4 ( CpMDAR4 ) in papaya

Key message Differential spatial and temporal expression patterns due to regulatory cis -elements and two different isoforms are detected among CpMDAR4 alleles in papaya. Abstract The aim of this research was to study the effects of cis -element differences between the X, Y and Y h alleles on the expression of CpMDAR4, a potential candidate gene for sex differentiation in papaya, using a transcriptional reporter system in a model species Arabidopsis thaliana . Possible effects of a retrotransposon insertion in the Y and Y h alleles on the transcription and expression of CpMDAR4 alleles in papaya flowers were also examined. When comparing promoters and cis -regulatory elements among genes in the non-recombining region of the sex chromosomes, paired genes exhibited differences. Our results showed that differences in the promoter sequences of the CpMDAR4 alleles drove the expression of a reporter gene to different flower tissues in Arabidopsis. β-glucuronidase staining analysis of T 2 and T 3 lines for constructs containing 5′ deletions of native Y and Y h allele promoters showed the loss of specific expression of the reporter gene in the anthers, confirming the existence and location of cis -regulatory element POLLEN1LELAT52. The expression analysis of CpMDAR4 alleles in papaya flowers also showed that all alleles are actively expressed in different flower tissues, with the existence of a shorter truncated isoform, with unknown function, for the Y and Y h alleles due to an LTR-RT insertion in the Y and Y h chromosomes. The observed expression patterns in Arabidopsis thaliana flowers and the expression patterns of CpMDAR4 alleles in papaya flowers suggest that MDAR4 might have a role on development of reproductive organs in papaya, and that it constitutes an important candidate for sex differentiation.