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

Abstract

Global climatic change poses a considerable risk to Malaysia’s booming oil palm industry as the
inflorescence initiation and differentiation in oil palms are affected by drought stress. As a result, the
proportion of female flowers significantly decreases, leading to reduced fruit bunch productivity. Hence, it
is crucial for plantation companies to understand the physiological response of different oil palm genotypes
to drought stress in ensuring that suitable genotypes are selected for stable yield production. Therefore, this
study aimed to understand the physiological and biochemical responses of oil palm seedlings under drought
stress conditions and to identify drought-responsive miRNAs in different oil palm progenies. Drought stress
treatment 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 such
as fluorescence parameter (F_v/F_m) and stomatal conductance (gs) were then carried out weekly. Biochemical
assays were also performed to measure the chlorophyll content and proline concentration. Finally, advanced
molecular 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 growth
rate with low biomass in drought stress BC21T (37%) and EB8T (31%). In addition, the increased proline
content in both genotypes by 3.9-fold for BC21T and 1.8-fold for EB8T confirmed the stress condition in
treated seedlings. Furthermore, significant differences in gs and F_v/F_m were recorded earlier in BC21 (6
days, 14 days) compared to EB8 (14 days, 20 days). The earlier gs reduction indicated that BC21 was more
sensitive to drought stress than EB8. Meanwhile, bioinformatics analysis of small RNA sequencing reads
identified 151 conserved miRNAs in both genotypes, with 58 out of 77 identified as novel miRNAs were
differentially expressed. Apart from that, nine miRNAs were identified as responsive to drought treatment
in both genotypes and played an essential role in various biological processes. Overall, this study provides
valuable insights into exploring oil palm physiological responses to drought and miRNA expression
patterns, which may facilitate future research on developing drought tolerant markers.