Characterization of nitrate use efficiency in tea plant (Camellia sinensis) based on leaf chlorate sensitivity

Abstract

Nitrate (NO3−), a key form of inorganic nitrogen (N) in soils, is typically lost in tea gardens through leaching. However, NO3− utilization efficiency (NiUE) and its characteristic mechanism in tea plants remain unclear. This study screened contrastive genotypes of NiUE using leaf chlorate sensitivity and explored the potential genes that regulate this process. Fresh branches of ten cultivars were hydroponically cultivated and subjected to potassium nitrate (KNO3) and potassium chlorate (KClO3) treatments, with the former as the control group. The sensitive cultivar, Zhenong 117 (ZN117), showed a decrease in SPAD and Fv/Fm values following KClO3 treatment, while the tolerant cultivar, Teiguanyin (TGY), exhibited minimal significant changes. After 5 days of cultivation, the 15N concentration and proportion in new shoots of ZN117 were significantly higher than those in TGY. Transcriptome analysis revealed that the expression of genes responsible for NO3− transport, including the nitrate transporters NRT2.4, NPF4.6, NPF6.1, NPF1.10, and NPF1.11, significantly increased in ZN117 after NO3− supply. Genes involved in NO3− reduction, chlorophyll synthesis, and photosynthesis were progressively induced. Co-expression network analysis indicated that the squamosa promoter binding protein activated the onset of NO3− signaling, while basic helix–loop–helix transcripts were triggered to higher levels during NO3− supply. This study proposes a rapid characterization method of NiUE in woody plants and a speculative molecular regulatory mechanism for the NO3− transfer and remobilization of tea plants. A set of specific genes involved in NO3− transport, reduction, and mobilization were identified and proposed as marker genes for NiUE in tea plants.