Objective  To compare the molecular response mechanisms of Eucalyptus urophylla under single and dual factor stresses of water and nutrient, and provide insight and molecular basis for resistance breeding of Eucalyptus.

Method  The experiment selected E. urophylla clone ZQUA44 as matetial, and set three stress treatments and one control (CK). Water and nutrient deficiency stress: 20%−40% field moisture capacity, applying 250 g calcium magnesium phosphate fertilizer (CMPF) as base fertilizer; Water deficiency stress: 20%−40% field moisture capacity, applying 250 g CMPF and 150 g compound fertilizer as base fertilizer; Nutrient deficiency stress: 60%−80% field moisture capacity, applying 250 g CMPF as base fertilizer; CK: 60%−80% field moisture capacity, applying 250 g CMPF and 150 g compound fertilizer as base fertilizer. The urea of 100 g was applied at two months after planting, 150 g compound fertilizer in August, and 100 g compound fertilizer in the next spring in water deficiency stress and control treatments. High-throughput transcriptome sequencing was performed to E. urophylla leaves in different stress treatments, and the growth indexes of plant were determined. After assembling, differentially expressed genes were obtained using bioinformatics methods, and GO functional annotations and KEGG pathway analyses were performed. Finally, four differentially expressed genes with different expression patterns were randomly selected for qRT-PCR to validate the reliability of transcripcome sequencing data.

Result  All three stress treatments partly suppressed the growth and development ofE. urophylla. Most of the growth indexes of E. urophylla in three stress treatments were significantly lower than those in control. A total of 5 547 differentially expressed genes were obtained in water and nutrient deficiency treatment, water deficiency treatment and nutrient deficiency treatment. The 2 585, 1 472 and 1 490 differentially expressed genes were obtained, including 1 195, 222 and 665 up-regulated genes and 1 390, 1 250 and 825 down-regulated genes, respectively. The 155, 75, 108 gene encoding transcription factors were respectively obtained in three stress treatments. The differentially expressed genes in three stress treatments were all significantly enriched in phenylpropane biosynthetic pathway. The qRT-PCR results were basically consistent with transcriptome sequencing results, indicating that the sequencing results were credible.

Conclusion  The transcriptional changes of E. urophylla in three stress treatments have obvious universality and specificity, and the effects of dual factor stress on plant growth are more than that of single factor stress. Plant may have different responce modes in different stress conditions.