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

Authors: ZERPA-CATANHO, DESSIREE - University Of Illinois; Clough, Steven; MING, RAY - University Of Illinois

Submitted to: Plant Reproduction
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/11/2022
Publication Date: 8/3/2022
Citation: Zerpa-Catanho, D.P., Clough, S.J., Ming, R. 2022. Characterization and analysis of the promoter region of Monodehydroascorbate reductase 4 (CpMDAR4) in papaya. Plant Reproduction. 35:233-264. https://doi.org/10.1007/s00497-022-00447-2.
DOI: https://doi.org/10.1007/s00497-022-00447-2

Interpretive Summary: In papaya, the trees can grow as male, female or hermaphrodite leading to differences in the quantity, size and quality of fruit produced. Male trees have flowers that normally cannot produce fruit, but will under certain conditions such as top cutting or high heat. Female plants have flowers lacking the ability to self pollinate, and need to be pollinated, but also, like male plants, can produce some fruit (without pollination) under high heat or with top cutting. Hermaphrodite trees can produce fruit without manual pollination, but their gender can also change due to high temperature and top pruning. Therefore, understanding what genes control sex type and sex change in papaya is extremely important for ideal crop production. We have analyzed spatial and temporal expression of a potential candidate gene (MDAR4) for sex determination or differentiation in papaya using a transcriptional reporter system. Due to the expression patterns we observed, we conclude that MDAR4 is an important gene for sex differentiation, but probably not sex determination. Understanding what genes play a role in papaya gender differentiation provides breeders and molecular biologists targets for genetic manipulations that can lead to more favorable fruit production.

Technical Abstract: Spatial and temporal gene expression is regulated by both cis and trans-regulatory elements. The aim of this research was to study the effects of cis-element differences between the X, Y and Yh alleles on the expression of CpMDAR4, a potential candidate gene for sex determination or differentiation in papaya, using a transcriptional reporter system in a model species Arabidopsis thaliana. Possible effects of a retrotransposon insertion in the Y and Yh alleles on the transcription and expression of CpMDAR4 alleles in papaya flowers were also examined. When comparing promoter sequences and cis-regulatory elements among genes in the non-recombining region of the sex chromosomes, paired genes exhibited differences, indicating that the expression of their alleles are differentially regulated. 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. ß-glucuronidase staining analysis of T2 and T3 lines for constructs containing 5’ deletions of native Y and Yh 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 responsible for anther or pollen-specific expression. Due to the observed expression patterns in Arabidopsis thaliana flowers and expression patterns of CpMDAR4 alleles in papaya flowers, we conclude that MDAR4 is an important gene for sex differentiation. The expression analysis of CpMDAR4 alleles in papaya flowers also showed that all X, Y, and Yh alleles are actively expressed in different flower tissues, with the existence of two isoforms for the Y or Yh alleles. These findings improved the understanding of gene expression regulation in the sex determining region of the papaya Y and Yh chromosomes.