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The importance of drought as a constraint to agriculture and forestry is increasing with climate change. Genetic improvement of plants' resilience is one of the mitigation strategies to curb this threat. Although recovery from drought stress is important to long-term drought adaptation and has been considered as an indicator of dehydration tolerance in annual crops, this has not been well explored in forest trees. Thus, we aimed to investigate the physiological and transcriptional changes during drought stress and rewatering in Eucalyptus grandis W. Hill ex Maiden. We set up a greenhouse experiment where we imposed drought stress on 2-year-old seedlings and rewatered the recovery group after 17 days of drought. Our measurement of leaf stomatal conductance (gs) showed that, while gs was reduced by drought stress, it fully recovered after 5 days of rewatering. The RNA-seq analysis from stem samples revealed that genes related to known stress responses such as phytohormone and reactive oxygen species signaling were upregulated, while genes involved in metabolism and growth were downregulated due to drought stress. We observed reprogramming of signal transduction pathways and metabolic processes at 1 day of rewatering, indicating a quick response to rewatering. Our results suggest that recovery from drought stress may entail alterations in the jasmonic acid, salicylic acid, ethylene and brassinosteroid signaling pathways. Using co-expression network analysis, we identified hub genes, including the putative orthologs of ABI1 , ABF2 , ABF3 , HAI2 , BAM1 , GolS2 and SIP1 during drought and CAT2 , G6PD1 , ADG1 and FD-1 during recovery. Taken together, by highlighting the molecular processes and identifying key genes, this study gives an overview of the mechanisms underlying the response of E. grandis to drought stress and recovery that trees may face repeatedly throughout their long life cycle. This provides a useful reference to the identification and further investigation of signaling pathways and target genes for future tree improvement. [ABSTRACT FROM AUTHOR]

Summary: Wood production in fast‐growing Eucalyptus grandis trees is highly dependent on both potassium (K) fertilization and water availability but the molecular processes underlying wood formation in response to the combined effects of these two limiting factors remain unknown.E. grandis trees were submitted to four combinations of K‐fertilization and water supply. Weighted gene co‐expression network analysis and MixOmics‐based co‐regulation networks were used to integrate xylem transcriptome, metabolome and complex wood traits. Functional characterization of a candidate gene was performed in transgenic E. grandis hairy roots.This integrated network‐based approach enabled us to identify meaningful biological processes and regulators impacted by K‐fertilization and/or water limitation. It revealed that modules of co‐regulated genes and metabolites strongly correlated to wood complex traits are in the heart of a complex trade‐off between biomass production and stress responses. Nested in these modules, potential new cell‐wall regulators were identified, as further confirmed by the functional characterization of EgMYB137.These findings provide new insights into the regulatory mechanisms of wood formation under stressful conditions, pointing out both known and new regulators co‐opted by K‐fertilization and/or water limitation that may potentially promote adaptive wood traits. [ABSTRACT FROM AUTHOR]