Transcriptomics and co-expression networks reveal tissue-specific responses and regulatory hubs under mild and severe drought in papaya (Carica papaya L.).

Plants respond to drought stress through the ABA dependent and independent pathways, which in turn modulate transcriptional regulatory hubs. 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.

Estudio de diversidad de accesiones de guayabo (psidium guajava L) mediante el marcador molecular ISTR / Studying the diversity of guava (psidium guajava L) accessions using ISTR molecular markers

Los estudios de variabilidad genética resultan útiles para el manejo racional del material, tanto para su conservación como para el mejoramiento. La Repetición de Secuencias Inversas Marcadas (ISTR) es una técnica basada en la PCR que permite el estudio de la diversidad genética de individuos y poblaciones; identificación de cultivares, entre otras aplicaciones. En este sentido, el objetivo del presente trabajo fue estudiar la diversidad de accesiones de guayabo empleando este marcador molecular. Para el análisis de los datos se generó una matriz de ausencia-presencia de las bandas polimórficas, a partir de la cual se desarrolló un análisis de agrupamiento basado en el coeficiente de Jaccard y el método UPGMA para la construcción del dendrograma con el programa NTSYS-pc. La evaluación de los genotipos de guayabo con el marcador ISTR generó un total de 52 bandas polimórficas, las cuales permitieron diferenciar todos los materiales evaluados, corroborando la utilidad de esta técnica para la identificación de accesiones en la especie. El análisis de agrupamiento permitió evidenciar la formación de cuatro grupos de diversidad definidos y la presencia de cuatro accesiones externas. Las diferencias encontradas en el agrupamiento de las accesiones por ISTR respecto a las obtenidas previamente por AFLP y SSR sugieren que el elegir la técnica más apropiada para determinados estudios puede resultar un proceso difícil. Los resultados discutidos en este trabajo indican la necesidad de realizar estudios integrados en el banco de germoplasma de este cultivo para lograr un manejo más racional de la base genética del mismo.

Studies about genetic variability can be useful for material rational management, as much as for conservation and breeding. The Inverse Sequence Tagged Repeats (ISTR) is a technique based on PCR, which permit the study of genetic diversity for individuals and populations; cultivars identification, within other applications. In this sense, the objective of the present work was to study guava accessions diversity using this molecular marker. For data analysis, an absence-presence matrix for polymorphic bands was generated, from which a cluster analysis was developed, based on Jaccard coefficient and UPGMA method for dendrogram construction using NTSYS-pc program. Guava genotypes evaluation with ISTR marker generated a total of 52 polymorphic bands, which permitted to differentiated all the materials evaluated, corroborating the utility of this technique for accessions identification in the specie. Cluster analysis permitted to evidence the formation of four defined diversity groups and the presence of four external accessions. The differences encountered for accessions clustering with ISTR respected to the ones obtained previously for AFLP and SSR suggest that the election of the most appropriated technique for determinate studies can result a difficult process. The results discussed in this work indicate the necessity to made integrated studies on the germplasm bank of this crop to obtain a more adequate management.