Physio-biochemical and molecular mechanisms of low nitrogen stress tolerance in peanut (Arachis hypogaea L.)

Nitrogen (N) is a major plant nutrient and its deficiency can arrest plant growth. However, how low-N stress impair plant growth and its related tolerance mechanisms in peanut seedlings has not yet been explored. To counteract this issue, a hydroponic study was conducted to explore low N stress (0.1 mM NO₃^-) and normal (5.0 mM NO₃^-) effects on the morpho-physiological and molecular attributes of peanut seedlings. Low-N stress significantly decreased peanut plant height, leaf surface area, total root length, and primary root length after 10 days of treatment. Meanwhile, glutamate dehydrogenase, glutamine oxoglutarate aminotransferase activities, chlorophyll, and soluble protein contents were substantially decreased. Impairment in these parameters further suppressed photochemical efficiency (Fv/Fm), and chlorophyll fluorescence parameters (PI_ABS), under low-N stress. Transcriptome sequencing analysis showed a total of 2139 DEGs were identified between the two treatments. KEGG enrichment annotation analysis of DEGs revealed that 119 DEGs related to 10 pathways, including N assimilation, photosynthesis, starch, and sucrose degradation, which may respond to low-N stress in peanuts. Combined with transcriptome, small RNA, and degradome sequencing, we found that PC-3p-142756_56/A.T13EMM (CML3) and PC-5p-43940_274/A.81NSYN (YTH3) are the main modules contributing to low N stress tolerance in peanut crops. Peanut seedlings exposed to N starvation exhibited suppressed gene expression related to nitrate transport and assimilation, chlorophyll synthesis, and carbon assimilation, while also showing improved gene expression in N compensation/energy supply and carbohydrate consumption. Additionally, low N stress tolerance was strongly associated with the miRNA.