Sexually differential gene expressions in poplar roots in response to nitrogen deficiency

Nitrogen (N) is a key nutrient impacting plant growth and physiological processes. However, the supply of N is often not sufficient to meet the requirements of trees in many terrestrial ecosystems. Because of differences in production costs, male and female plants have evolved different stress resistance strategies for N limitation. However, little is known about differential gene expression according to sex in poplars responding to N limitation. To explore sex-related constitutive defenses, Populus cathayana Rehder transcriptomic, proteomic and metabolic analyses were performed on the roots of male and female Populus cathayana. We detected 16,816 proteins and 37,286 transcripts, with 2797 overlapping proteins and mRNAs in the roots. In combination with the identification of 90 metabolites, we found that N deficiency greatly altered gene expression related to N metabolism as well as carbohydrate metabolism, secondary metabolism and stress-related processes in both sexes. Nitrogen-deficient P. cathayana females exhibited greater root biomass and less inhibition of citric acid production and glycolysis as well as higher secondary metabolic activity and abscisic acid contents than N-deficient P. cathayana males. Interestingly, males presented a better osmotic adjustment ability and higher expression of resistance genes, suggesting that P. cathayana males exhibit a better stress tolerance ability and can invest fewer resources in defense compared with females. Therefore, our study provides new molecular evidence that P. cathayana males and females adopt different resistance strategies to cope with N deficiency in their roots.