Physiological Responses and Identification of Drought- Responsive miRNAs in Oil Palm Seedlings under Drought Stress ConditionsResilient Forests

Global climatic change poses a considerable risk to Malaysia’s booming oil palm industry as theinflorescence initiation and differentiation in oil palms are affected by drought stress. As a result, theproportion of female flowers significantly decreases, leading to reduced fruit bunch productivity. Hence, itis crucial for plantation companies to understand the physiological response of different oil palm genotypesto drought stress in ensuring that suitable genotypes are selected for stable yield production. Therefore, thisstudy aimed to understand the physiological and biochemical responses of oil palm seedlings under droughtstress conditions and to identify drought-responsive miRNAs in different oil palm progenies. Drought stresstreatment was imposed on 3-month-old seedlings consisting of two oil palm genotypes, Deli dura x pisifera(BC21) and URT-Calabar (EB8), by withholding irrigation for 20 days. Physiological measurements suchas fluorescence parameter (Fv/Fm) and stomatal conductance (gs) were then carried out weekly. Biochemicalassays were also performed to measure the chlorophyll content and proline concentration. Finally, advancedmolecular techniques were conducted to identify drought-responsive miRNA from drought stress samples.Based on the results, the decreased soil volumetric water content (vwc) resulted in a reduced plant growthrate with low biomass in drought stress BC21T (37%) and EB8T (31%). In addition, the increased prolinecontent in both genotypes by 3.9-fold for BC21T and 1.8-fold for EB8T confirmed the stress condition intreated seedlings. Furthermore, significant differences in gs and Fv/Fm were recorded earlier in BC21 (6days, 14 days) compared to EB8 (14 days, 20 days). The earlier gs reduction indicated that BC21 was moresensitive to drought stress than EB8. Meanwhile, bioinformatics analysis of small RNA sequencing readsidentified 151 conserved miRNAs in both genotypes, with 58 out of 77 identified as novel miRNAs weredifferentially expressed. Apart from that, nine miRNAs were identified as responsive to drought treatmentin both genotypes and played an essential role in various biological processes. Overall, this study providesvaluable insights into exploring oil palm physiological responses to drought and miRNA expressionpatterns, which may facilitate future research on developing drought tolerant markers.