Here, we employed Illumina RNA-Seq to analyze a total of 18 cDNA libraries from leaves, sap, and roots of papaya plants under drought stress. Reference and de novo transcriptomic analyses identified 8,549 and 6,089 drought-responsive genes and unigenes, respectively. Core sets of 6 and 34 genes were simultaneously up- or down-regulated, respectively, in all stressed samples. Moreover, GO enrichment analysis revealed that under moderate drought stress, processes related to cell cycle and DNA repair were up-regulated in leaves and sap; while responses to abiotic stress, hormone signaling, sucrose metabolism, and suberin biosynthesis were up-regulated in roots. Under severe drought stress, biological processes related to abiotic stress, hormone signaling, and oxidation-reduction were up-regulated in all tissues. Moreover, similar biological processes were commonly down-regulated in all stressed samples. Furthermore, co-expression network analysis revealed three and eight transcriptionally regulated modules in leaves and roots, respectively. Seventeen stress-related TFs were identified, potentially serving as main regulatory hubs in leaves and roots. Our findings provide insight into the molecular responses of papaya plant to drought, which could contribute to the improvement of this important tropical crop.
Figure 1: Effect of drought stress on papaya plants. (a) Three-month-old ‘Maradol’ papaya plants under control condition (CN) and at 10 and 20 days after stress imposition (DASI). The gradient-colored arrow indicates the intensity of the imposed stress: green = well-watered or no stress, yellow = mild stress, and red = severe stress. White arrows in the plants at 10 DASI indicate leaf wilting. (b–d) Effect of drought stress on papaya plant physiology: (b) CO2 assimilation rate (A), (c) transpiration rate (T), and (d) leaf water potential (Ψ) of the papaya plant depicted in a). Bars and error bars represent means and standard deviation (s.d.), respectively, of three independent plants (n = 3). Different letters indicate statistically significant differences (ANOVA, Tukey p < 0.001).