# Genome-Wide Identification and Biotic Stress Responses of TLP Gene Family in Citrus sinensis

## TL;DR

This study identifies 23 TLP genes in citrus and shows how they respond to different pathogens like bacteria and fungi.

## Contribution

The study provides a genome-wide analysis of TLP genes in Citrus sinensis and their specific responses to biotic stress.

## Key findings

- 23 CsTLP genes were identified, with most localized in extracellular space and unevenly distributed across eight chromosomes.
- CsTLP9 and CsTLP22 were strongly upregulated during Huanglongbing infection, with over 20-fold and 9-fold increases, respectively.
- Multiple CsTLP genes showed over 10-fold upregulation in response to Citrus Anthracnose fungal infection.

## Abstract

Thaumatin-like proteins (TLPs), a subfamily of pathogenesis-related (PR) proteins, play a vital role in plant defense against pathogens. In this study, 23 CsTLP genes were identified in the Citrus sinensis genome. These genes encode proteins ranging from 203 to 512 amino acids, with molecular weights between 21.88 and 53.75 kDa, classifying them as small molecular weight proteins. The CsTLP genes are unevenly distributed across eight chromosomes, with chromosome 3 containing the highest number (6 genes). Subcellular localization predictions indicate that most CsTLPs are located in the extracellular space. Phylogenetic analysis with Arabidopsis thaliana TLPs classified the CsTLPs into 10 clades, with clade 5 being the largest. Three segmentally duplicated gene pairs were identified, suggesting a mechanism for the expansion of this gene family. Expression profiling revealed tissue-specific patterns, with the highest expression levels observed in roots and leaves. Under biotic stress, qRT-PCR analysis of 12 selected CsTLPs demonstrated pathogen-specific responses: CsTLP9 and CsTLP22 were strongly upregulated during Huanglongbing (HLB, bacterial) infection, by 21.70-fold and 9.47-fold, respectively. Multiple genes, including CsTLP5/13/18/21/23, exhibited over 10-fold upregulation following Citrus Anthracnose (CA, fungal) infection; however, most genes showed only weak responses to Citrus tristeza virus (CTV, viral). These findings underscore the regulatory significance of CsTLPs in pathogen responses and provide an important theoretical foundation for enhancing molecular disease-resistance breeding in Citrus sinensis.