Small nucleolar RNA HIDDEN TREASURE 2 reduces drought tolerance via multiple pathways in Arabidopsis

Small nucleolar RNAs (snoRNAs) contribute to ribosome biogenesis and modulate various aspects of plant growth and development. Given that osmotic stress downregulates numerous genes associated with ribosome biogenesis in roots, we hypothesize that snoRNAs might function in modulating plant responses to osmotic and drought stresses. To prove this hypothesis, we assessed the role of a C/D-box snoRNA, namely the HIDDEN TREASURE 2 (HID2), in Arabidopsis thaliana responses to drought using both loss-of-function and overexpression approaches. Under drought conditions, the Arabidopsis hid2 mutant displayed a significantly higher survival rate than both wild-type (WT) and HID2-complemented plants, while HID2-overexpressing plants showed a lower survival rate than WT. A series of physiological assays indicated that the hid2 mutant maintained a slower rate of water loss and more intact cell membranes than WT plants under drought, which supported their drought-tolerant phenotype. Comparative leaf transcriptome and proteome analyses revealed that processes related to wax biosynthesis, senescence, and anthocyanin accumulation were differentially regulated between hid2 and WT plants under water-deficit conditions. Consistently, the hid2 mutant accumulated higher amounts of wax and anthocyanins and exhibited delayed leaf senescence relative to WT plants under drought. Additionally, the hid2 mutant showed improved ability to increase sensitivity to abscisic acid (ABA), scavenge reactive oxygen species (ROS), and extended root hairs. Overall, these findings demonstrate HID2's role as a negative modulator in Arabidopsis drought tolerance by negatively affecting cell membrane stability, wax and anthocyanin biosynthesis, senescence, ROS-scavenging capacity, ABA responsiveness, and root hair formation.