Morphological, physiological, and transcriptional responses to low nitrogen stress in Populus deltoides Marsh. clones with contrasting nitrogen use efficiency

Abstract

Background Nitrogen (N) is one of the main factors limiting the wood yield in poplar cultivation. Understanding the molecular mechanism of N utilization could play a guiding role in improving the nitrogen use efficiency (NUE) of poplar. Results In this study, three N-efficient genotypes (A1-A3) and three N-inefficient genotypes (C1-C3) of Populus deltoides were cultured under low N stress (5 μM NH4NO3) and normal N supply (750 μM NH4NO3). The dry matter mass, leaf morphology, and chlorophyll content of both genotypes decreased under N starvation. The low nitrogen adaptation coefficients of the leaves and stems biomass of group A were significantly higher than those of group C (p < 0.05). Interestingly, N starvation induced fine root growth in group A, but not in group C. Next, a detailed time-course analysis of enzyme activities and gene expression in leaves identified 2062 specifically differentially expressed genes (DEGs) in group A and 1118 in group C. Moreover, the sensitivity to N starvation of group A was weak, and DEGs related to hormone signal transduction and stimulus response played an important role in the low N response this group. Weighted gene co-expression network analysis identified genes related to membranes, catalytic activity, enzymatic activity, and response to stresses that might be critical for poplar’s adaption to N starvation and these genes participated in the negative regulation of various biological processes. Finally, ten influential hub genes and twelve transcription factors were identified in the response to N starvation. Among them, four hub genes were related to programmed cell death and the defense response, and PodelWRKY18, with high connectivity, was involved in plant signal transduction. The expression of hub genes increased gradually with the extension of low N stress time, and the expression changes in group A were more obvious than those in group C. Conclusions Under N starvation, group A showed stronger adaptability and better NUE than group C in terms of morphology and physiology. The discovery of hub genes and transcription factors might provide new information for the analysis of the molecular mechanism of NUE and its improvement in poplar.

Combining GS-assisted GWAS and transcriptome analysis to mine candidate genes for nitrogen utilization efficiency in Populus cathayana

“…S5 ). Previous studies have shown that gene expression levels [ 5 , 40 , 41 ] and enzyme activities associated with nitrogen metabolism differ significantly at different N levels [ 27 , 42 , 43 ]. We focused on examining the differences gene expression involved in major pathways of N metabolism under fertilization conditions (Fig.…”

“…The hub genes of this module include four genes directly or indirectly involved in nitrogen metabolism and two NAC transcription factors ( PtrNAC025 and PtrNAC12 ). Previously, Chen et al [ 5 ] constructed a four-layer transcriptional regulatory network (TRN) for poplar wood formation. This network, with PtrSND1 as the top-level regulatory factor and PtrMYB74 and PtrMYB21 as second-level regulatory factors, regulate the expression of 17 target genes and their downstream genes involved in secondary cell wall biosynthesis during wood formation [ 21 , 46 , 47 ].…”

“…Currently, forest tree NUE studies tend to focus on theoretical studies, with few instances of functional validation [ 2 , 5 ]. The lack of genes related to N use efficiency is the main reason for this phenomenon.…”

Revealing the relationship between nitrogen use efficiency‐related QTLs and carbon and nitrogen metabolism regulation in poplar

“…Woody bioenergy plants are expected to contribute an estimated 300 million tonnes of dry biomass in 2030 (Downing et al, 2011). Poplar ( Populus ) has the advantage of rapid growth in woody plants and is widely planted worldwide and in China (Chen et al, 2021; Sun et al, 2019). Hybrid poplars have higher lignin and cellulose contents than other major bioenergy crops (Table 1).…”

“…Hybrid poplars have higher lignin and cellulose contents than other major bioenergy crops (Table 1). Most poplar plantations are planted in nitrogen-poor areas, which predisposes them to low productivity (Chen et al, 2020(Chen et al, , 2021Song et al, 2020). Therefore, nitrogen deficiency has become a major factor limiting the sustainable development of poplar productivity.…”