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Key message
Differential spatial and temporal expression patterns due to regulatory
cis
-elements and two different isoforms are detected among
CpMDAR4
alleles in papaya.
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.