Overexpressing PagGS1;2 maintains carbon and nitrogen balance under high-ammonium conditions and shows increased tolerance to ammonium toxicity in 84K Poplar

Xue Leng; Hanzeng Wang; Lina Cao; Ruihui Chang; Shuang Zhang; Caifeng Xu; Jiajie Yu; Xiuyue Xu; Chunpu Qu; Zhiru Xu; Guanjun Liu

doi:10.1093/jxb/erae124

Overexpressing PagGS1;2 maintains carbon and nitrogen balance under high-ammonium conditions and shows increased tolerance to ammonium toxicity in 84K Poplar

J Exp Bot. 2024 Mar 18:erae124. doi: 10.1093/jxb/erae124. Online ahead of print.

Authors

Xue Leng^{1

2}, Hanzeng Wang², Lina Cao¹, Ruihui Chang³, Shuang Zhang³, Caifeng Xu¹, Jiajie Yu¹, Xiuyue Xu¹, Chunpu Qu^{1

4}, Zhiru Xu^{1

3}, Guanjun Liu¹

Affiliations

¹ State Key Laboratory of Tree Genetics and Breeding, Northeast Forestry University, Harbin 150040, China.
² College of Agriculture, Jilin Agricultural Science and Technology University,Jilin 132109, China.
³ College of Life Science, Northeast Forestry University, Harbin 150040, China.
⁴ College of Foresty, Guizhou University, Guiyang 550025, China.

PMID: 38497908
DOI: 10.1093/jxb/erae124

Abstract

In plants, the glutamine synthetase - glutamic acid synthetase (GS/GOGAT) cycle plays important roles in nitrogen metabolism, growth, development, and stress resistance. Excess ammonium (NH4+) restricts plant growth, but GS can help to alleviate NH4+ toxicity. In this study, 84K poplar (Populus alba × P. glandulosa) showed reduced biomass accumulation and leaf chlorosis under high-NH4+ stress. These symptoms were less severe in lines overexpressing the gene encoding glutamine synthetase (PagGS1;2-OE), and more severe in lines with inhibition of PagGS1;2 expression (PagGS1;2-RNAi). Compared with the wild type（WT）, the PagGS1;2-OE lines showed significantly increased GS and GOGAT activities and higher contents of free amino acids, soluble protein, total nitrogen, and chlorophyll under high-NH4+ stress. In contrast, the antioxidant capacity and NH4+ assimilation capacity of PagGS1;2-RNAi lines were decreased under high-NH4+ stress. The total carbon (C) content and C/N ratio (C/N) of roots and leaves of PagGS1;2-OE lines were significantly higher than those of WT under high-NH4+ stress. Overexpression of PagGS1;2 led to increased accumulation of various amino acids (3-methylaspartic acid, glutamic acid, proline, serine, and histidine); reduced contents of carbohydrates (fructose, starch, galactose, glucose 1-phosphate, fructose 6-phosphate); and increased contents of sugar alcohols (sedum heptanose, maltose, mannitol, galactose, sorbitol) in the roots under high-NH4+ stress. Under high-NH4+ stress, genes related to amino acid biosynthesis, sucrose and starch degradation, galactose metabolism, and the antioxidant system were significantly up-regulated in the roots of PagGS1;2-OE lines, compared with those of wild type. Thus, PagGS1;2 overexpression affected C metabolism and amino acid metabolism pathways under high-NH4+ stress, which helped to maintain the balance of C and N metabolism and alleviate the symptoms of NH4+ toxicity. Modification of the GS/GOGAT cycle by genetic engineering is a promising strategy to improve NH4+ tolerance of forest trees.

Keywords: 2; PagGS1; Poplar; ammonium toxicity; carbon metabolism; nitrogen metabolism; stress.