Energy deprivation affects nitrogen assimilation and fatty acid biosynthesis leading to leaf chlorosis under waterlogging stress in the endangered Abies koreana

Abstract

Energy deprivation triggers various physiological, biochemical and molecular changes in plants under abiotic stress. We investigated the oxidative damages in the high altitude grown conifer Abies koreana exposed to waterlogging stress. Our experimental results showed that waterlogging stress led to leaf chlorosis, 35 days after treatment (DAT). A significant decrease in leaf fresh weight, chlorophyll, and sugar content supported this phenotypic change. Biochemical analysis showed a significant increase in leaf proline, lipid peroxidase and DPPH free radical content of waterlogged plants. To elucidate the molecular mechanisms, we conducted RNA-sequencing and de novo assembly. Using RNA-Seq analysis approach and filtering (P < 0.05 and FDR < 0.001), we obtained 134 unigenes upregulated and 574 unigenes downregulated. GO and KEGG pathway analysis, placed the obtained differentially expressed unigenes (DEGs) in α-linoleic pathway, fatty acid degradation, glycosis, glycolipid metabolism and oligosaccharide biosynthesis process. Mapping of unigenes with Arabidopsis using BLASTn tool, showed several critical genes in photosynthesis and carbon metabolism downregulated. Following this, we found the repression of multiple nitrogen (N) assimilation and nucleotide biosynthesis genes including purine metabolism. In addition, waterlogging stress reduced the levels of polyunsaturated fatty acids with a concomitant increase only in myristic acid. Together, our results indicate that the prolonged snowmelt may cause inability of Abies koreana seedlings to lead the photosynthesis normally, due to the lack of root intercellular oxygen and emphasizes a detrimental effect on the N metabolic pathway, compromising this endangered tree’s ability to be fully functional under waterlogging stress.