الملخص الإنجليزي
Date palm (Phoenix dactylifera L.) is the primary agricultural crop in Oman. Recent statistics have indicated that there are 8,050,000 date palm trees, produce 172,866 tonnes of dates annually. Although date palm is relatively tolerant to salt-stress, the
cultivation and hence the agricultural production of date palm trees was highly affected by soil salinity. Therefore, this study aims to investigate the response of this crop to salinity stress based on methylome and transcriptome approaches in order to understand the salinity response mechanism and, therefore, design an efficient strategy to produce salinity tolerant date palms. Initially, whole-genome bisulfite sequencing (WGBS) technique was used to identify differentially methylated regions (DMRs) in date palm genome in response to salt stress. The results revealed that the level of methylation within these DMRs was significantly (p < 0.05, FDR ≤0.05) increased in response to salinity. DNA methylation is known to play an essential role in regulating gene expression in response to abiotic stresses, including salinity. Therefore, mRNA sequencing was also conducted to identify significantly (p < 0.001, FDR ≤0.05) regulated genes (6,405), which were assigned to their DNA methylation level in the
different gene regions. Integrative analysis of methylome and transcriptome revealed a negative correlation between mCG methylation located within the promoters and the gene expression, while a positive relationship was noticed between mCHG/mCHH methylation ratios and gene expression specifically when plants grew under control conditions. Functional enrichment analysis of significant DMGs (p ≤0.05), indicated that upregulated genes containing mCG were enriched in hydrogen ion transmembrane transport and regulation of protein kinase phosphorylation activity. Sodium hydrogen exchanger 6 (PdNHX6) and vascular highway 1-interacting kinase (PdVIK) genes were among those genes that were affected by salinity in terms of DNA methylation and gene expression level. Therefore, they were selected for functional characterization in a
model plant, Arabidopsis thaliana. The results showed that heterologous overexpression of PdNHX6 in Arabidopsis enhanced tolerance to salt stress. The transgenic plants retained higher chlorophyll and water contents compared to the wild-type plants and were able to maintain a balanced Na+/K+ ratio under salt stress conditions. However, overexpression of PdVIK in Arabidopsis enhanced proline accumulation that might modulate the plant response to salt stress. Interestingly, PdVIK transgenic plants showed enhanced drought tolerance by maintaining better relative water content. The results
obtained from this study highlights two important genes, that can be used to increase the tolerance of date palm to drought and salinity using conventional and unconventional breeding methods.
