Functional characterization and analysis of Carica papaya MYB24 promoter region in Arabidopsis

Abstract

Papaya is a trioecious plant with three sex types: female (XX), male (XY) and hermaphrodite (XYh). It is also among limited members of plant species that have two different breeding systems, it is either dioecious, propagating with male and female or gynodioecious, propagating with hermaphrodite and female. Papaya sex chromosomes were identified, leading to the sequencing of the genome and the non-recombining regions of the X, Y, and Yh. The CpMYB24 is a promising candidate gene for the control of the sex determination and could be responsible for stamen (i.e., anther and anther filament) development. To investigate the expression profiling of CpMYB24 gene, the promoter regions of CpMYB24 gene was cloned from three sex chromosomes (X, Y, and Yh) and constructed a deletion series of reporter constructs to detect the gene expression pattern of those promoters. The results indicated that three CpMYB24 promoters were all expressed in the stamen at the late flower developmental stages in Arabidopsis thaliana. However, the GUS expression was also observed in the style of the transgenic lines driven by promoters from either X or Yh alleles of CpMYB24. Moreover, the cis-acting motif MYB1 located at 218bp upstream of CpMYB24 promoter from Y Chromosome was identified as the responsible element for the pollen-specific expression. MYB1 was detected regulating defense-related expression previously; however, the new function of MYB1 was discovered in this study to be regulating pollen-specific expression. These results confirmed the hypothesis that CpMYB24 promoters can activate expression only in reproductive organs of Arabidopsis; promoter of Y allele of CpMYB24 showed high male-specificity; and novel function of cis-regulating motif MYB1 was discovered in CpMYB24 promoter from Y chromosome.