A genome-wide analysis for two families of key transcription factors (TF; WRKY and NAC) involved in drought response revealed 46 WRKY and 66 NAC members of the Carica papaya genome. A phylogenetic analysis grouped the CpWRKY proteins into three groups (I, II a, b, c, d, e and III), while the CpNAC proteins were clustered into 15 groups. The conserved domains, chromosomal localization and promoter cis-acting elements were also analyzed. In addition, from a previous transcriptome study of two contrasting genotypes in response to 14 days of water deficit stress (WDS), we found that 29 of the 46 CpWRKYs genes and 25 of the 66 CpNACs genes were differentially expressed in response to the WDS. In the present paper, the native wild genotype (WG) (collected in its center of origin) consistently showed a higher expression (transcripts per million; TPM and fold change; FC) than the commercial genotype (CG) in almost all the members of the CpWRKY and CpNAC gene families. To corroborate this, we selected CpWRKY50 and CpNAC83.1 for further evaluation by RT-qPCR. Consistently, the WG showed higher relative expression levels (REL) after 14 days of WDS than the CG, in both the leaves and roots. The results suggest that the CpWRKY and CpNAC TF families are important for drought tolerance in this species. The results may also suggest that, during the domestication process, the ability of the native (wild) C. papaya genotypes to respond to drought (including the overexpression of the CpWRKY and CpNAC genes) was somehow reduced in the current commercial genotypes.

Resilience of growing in arid and semiarid regions and a high capacity of accumulating sugar-rich biomass with low lignin percentages have placed Agave species as an emerging bioenergy crop. Although transcriptome sequencing of fiber-producing agave species has been explored, molecular bases that control wall cell biogenesis and metabolism in agave species are still poorly understood. Here, through RNAseq data mining, we reconstructed the cellulose biosynthesis pathway and the phenylpropanoid route producing lignin monomers in A. tequilana, and evaluated their expression patterns in silico and experimentally. Most of the orthologs retrieved showed differential expression levels when they were analyzed in different tissues with contrasting cellulose and lignin accumulation. Phylogenetic and structural motif analyses of putative CESA and CAD proteins allowed to identify those potentially involved with secondary cell wall formation. RT-qPCR assays revealed enhanced expression levels of AtqCAD5 and AtqCESA7 in parenchyma cells associated with extraxylary fibers, suggesting a mechanism of formation of sclerenchyma fibers in Agave similar to that reported for xylem cells in model eudicots. Overall, our results provide a framework for understanding molecular bases underlying cell wall biogenesis in Agave species studying mechanisms involving in leaf fiber development in monocots.

El papel de los estomas de las hojas de la papaya cv. Maradol Carica papaya bajo cultivo in vitro