A C-Terminally Encoded Peptide, MeCEP6, Promotes Nitrate Uptake in Cassava Roots

Cassava, an essential food crop, is valued for its tolerance to infertile soils. This study explores the role of C-terminally encoded peptides (CEPs) in cassava, mainly focusing on MeCEP6 and its function in nitrate uptake and plant growth. A comprehensive search on the UniProt website identified 12 CEP genes in cassava, predominantly located on chromosomes 12 and 13. Notably, MeCEP6 demonstrated high expression levels in root tips and exhibited a significant response to low nitrate stress. Exogenous MeCEP6 and its overexpression enhanced NRT2 transporter expression while suppressing auxin-related genes, promoting nitrate uptake and inhibiting seedling growth under nitrogen limitation. This growth inhibition likely represents an adaptive mechanism, enhancing cassava's survival under nitrogen limitation by optimizing nitrogen allocation and use efficiency, albeit at the cost of reduced growth potential in nitrogen-replete conditions. Moreover, it was identified that MeWRKY65 and MeWRKY70 could interact with the promoter of MeCEP6 to modulate the expression of MeCEP6. The dual-luciferase assays further prove that MeWRKY65 and MeWRKY70 can activate the transcription of MeCEP6 under low nitrate stress conditions. The study's results help explain the underlying mechanism of MeCEP6 that benefits nitrogen use efficiency and nitrogen deficiency tolerance in cassava. These findings provide a molecular basis for improving cassava yield in nitrogen-deficient soils and highlight MeCEP6 as a potential target for crop improvement.