CpHSFA2 isolated from a wild native Carica papaya genotype, with potential to confer tolerance to the combined effect of drought stress and heat shock

Many papaya producing regions are repeatedly affected by drought and high temperatures. In the present study, we investigated the individual effect of heat shock (HS), water deficit stress (WDS) and the combined effect of both types of stress (WD + HS), on the physiological performance of two contrasting papaya genotypes (Maradol and Wild). In all cases, water relations, membrane integrity, gas exchange, photochemical state of PSII and RELs of three Carica papaya transcription factors (CpHsfA1d, CpHsfA2 and CpHsfB3, in both a Wild-native genotype collected from an undisturbed site in its center of origin (Yucatán, Mexico; Wild), as well as in a commercial cultivar (Maradol). Results showed that both papaya genotypes have different physiological and molecular mechanisms to cope with individual stress and combined stresses. Wild (W) genotype exhibited greater tolerance to the three types of stresses than the commercial genotype (M), which correlates with the fact that W also showed higher relative expression levels (REL) in the three CpHsf studied: CpHsfA1d, CpHsfA2 and CpHsfB3 than M. REL of CpHsfA2 was particularly high in the HS and in the combined WD + HS treatment, as well as during the recovery phase of the WDS treatment. CpHSFA2 was then selected for further analysis of subcellular localization, finding that it accumulates in the membrane and nucleus. Taken together, it seems that CpHsfA2 plays an important role in the response to HS and WD + HS stress. Therefore, CpHsfA2 gene from the W genotype could be important to eventually improve tolerance to high temperatures and drought in commercial papaya cultivars.