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

## TL;DR

This study explores how tea plants use nitrate efficiently by analyzing leaf chlorate sensitivity and identifying key genes involved in the process.

## Contribution

A new method to rapidly characterize nitrate use efficiency in woody plants and the identification of marker genes for this trait in tea plants.

## Key findings

- ZN117 showed higher 15N concentration in new shoots compared to TGY after nitrate treatment.
- Genes like NRT2.4 and NPF1.10 were significantly upregulated in ZN117 under nitrate supply.
- Coexpression networks suggest roles for squamosa promoter-binding protein and basic helix–loop–helix transcripts in nitrate signaling.

## 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 10 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. Coexpression 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.