The NPR1 family of transcription cofactors in papaya: insights into its structure, phylogeny and expression
Peraza-Echeverria, Santy | Santamaría, Jorge M. | Fuentes Ortíz, G. (Gabriela) | de los Ãngeles Menéndez-Cerón, Mariana | Vallejo-Reyna, Miguel Ãngel | Herrera-Valencia, Virginia Aurora
The NPR1 (non-expressor of pathogenesis related gene 1) gene was initially identified in Arabidopsis as a master regulator of the systemic acquired resistance (SAR). Five additional NPR1 homologues have been identified in Arabidopsis whose function range from regulators of SAR to plant development. In the present study, we characterized the structure, phylogeny and expression of the NPR1 family in papaya (Carica papaya L.), one of the most important tropical fruit crops. We identified four NPR1 homologues in the papaya genome sequence (CpNPR1 to CpNPR4). Overall, the four papaya predicted NPR1 proteins showed the characteristic BTB/POZ and ankyrin domains of the Arabidopsis NPR1 family. Twelve additional open reading frames showing homology to retrotransposon elements or genes involved in different physiological processes were found in close proximity to the papaya NPR1 homologues. The phylogenetic analysis revealed that the papaya NPR1 sequences resolved in three clades, each clade containing two Arabidopsis NPR1 homologues involved either in the positive regulation of SAR (clade I), negative regulation of SAR (clade II) or plant development (clade III), suggesting a similar function for the corresponding papaya NPR1 homologues. Furthermore, the expression of the four papaya NPR1 homologues was detected in both vegetative and reproductive tissues. The present study has provided the first comparative analysis of the NPR1 family in a tropical fruit crop and expanded our knowledge on this type of genes in dicotyledoneous plants. The identification of the full set of papaya NPR1 homologues will pave the way for their systematic functional analysis and new opportunities for engineering disease resistance in this crop.
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