RNA-Seq Analysis Uncovered Transcriptomic Changes in Poncirus trifoliata Roots Under Long-Term Soil Drought Conditions

Drought is one of the most serious abiotic stresses in citrus plantations. It is thus imperative to fully understand the drought-resistant mechanisms in these plants. Here, RNA-seq was used to analyze the transcriptomic changes in the roots of Poncirus trifoliata, a widely used rootstock in citrus plantations, under a 72-day soil drought and a 7-day recovery stage. Our results showed that the genes upregulated under drought were only enriched in the galactose metabolism and protein processing in endoplasmic reticulum pathways. In the galactose metabolism pathway, four genes related to the synthesis of raffinose family oligosaccharides, which act as osmoprotectants and ROS scavengers, were significantly upregulated under long-term drought. Several heat-shock protein (HSP) family genes were significantly upregulated under drought, leading to increased levels of HSPs to alleviate the endoplasmic reticulum-associated degradation of misfolded proteins induced by drought stress. Some other upregulated genes under drought, like late embryogenesis-abundant family genes and lipid transfer protein family genes, might also be crucial to the drought resistance of P. trifoliata roots. MSYJ196370 (heat-shock factor family gene) was the top hub gene in the protein–protein interaction analysis of upregulated genes under drought. These findings supplement the transcriptomic response of P. trifoliata root under long-term drought stress.