Genome-Wide Identification and Expression Analysis of Phytosulfokine Peptide Hormone Genes in Camellia sinensis

Abstract

Phytosulfokine (PSK) is a tyrosine-sulfated pentapeptide found throughout the plant kingdom, playing key roles in plant growth, development, and responses to biotic and abiotic stresses. However, there is still a lack of a comprehensive analysis of the CsPSK gene family in Camellia sinensis. In this study, we conducted a genome-wide identification and characterized 14 CsPSK genes in tea plants, which are unevenly distributed across seven chromosomes. CsPSK genes encode proteins ranging from 75 to 124 amino acids in length, all belonging to the PSK-α type and containing conserved PSK domains. A synteny analysis revealed that the expansion of the CsPSK gene family is primarily attributed to whole-genome duplication, with homology to Arabidopsis thaliana PSK genes. A promoter region analysis identified cis-regulatory elements related to hormone and stress responses. An expression profile analysis showed that CsPSK genes are highly expressed in roots, stems, flowers, and leaves, and are induced by both biotic and abiotic stresses. Furthermore, an RT-qPCR assay demonstrated that the expression levels of CsPSK8, CsPSK9, and CsPSK10 are significantly upregulated following Discula theae-sinensis infection. These findings establish a basis for further research into the role of the CsPSK gene family in tea plant disease resistance and underlying molecular mechanisms, offering valuable perspectives for developing novel antimicrobial peptides.

Keywords: Camellia sinensis; gene expression; genome-wide analysis; phytosulfokine; stress response.

Figure 1

Chromosomal localization of the CsPSK gene family members in tea plants. Chromosome numbers are labeled on the left in organe font color (abbreviated as Chr), while gene positions are indicated on the right in red font color.

Figure 2

Phylogenetic relationships of the CsPSK gene family in C. sinensis and other plant species. The sequences of PSKs used in this analysis are provided in Table S1. Red pentagrams indicate CsPSK proteins. Different clades are highlighted in distinct colors.

Figure 3

Synteny analysis of CsPSK genes in C. sinensis. Red lines represent duplicated gene pairs, while gray lines indicate syntenic gene pairs in the whole genome.

Figure 4

Synteny analysis of PSK genes among C. sinensis, A. thaliana, S. lycopersicum. Cs represents the tea plant genome (sky blue), At represents the Arabidopsis genome (soft amber), and Sl represents the tomato genome (deep blue). Gray lines represent syntenic relationships among different genomes and red lines indicate syntenic relationships among the PSK genes.

Figure 5

The phylogenetic tree, conserved motif, domain and gene structure of the CsPSK proteins. Different motif patterns are indicated by different colored numbered boxes. The blue squares represent the PSK superfamily in the domain pattern. The distribution of untranslated regions (UTRs) and coding sequences (CDSs) of the CsPSK gene family members. The soft green gradient represents UTRs and gradual orange represents CDSs.

Figure 6

The multiple sequence alignment of the CsPSK gene family. Conserved pentapeptides are indicated by black triangles.

Figure 7

Analysis of cis-acting elements in the promoter regions of CsPSK genes. The numbers in the grid represent the quantity of cis-acting elements, while the color intensity indicates the abundance of these elements. The right side displays the statistics of cis-acting elements for each gene under four types, including light-responsive elements, hormone-responsive elements, stress-responsive elements, and development-related elements.

Figure 8

Expression patterns of CsPSK genes under different tissues and stress conditions. (A) Expression patterns of CsPSK genes in eight different tissues of tea plants. Expression responses of tea plants under (B) drought stress, (C) salt stress, (D) leafhopper infestation, and (E) gray blight infection. The size and color of the circles represent high and low expression levels, with red indicating high expression and dark blue indicating low expression.

Figure 9

The relative expression patterns of CsPSK genes under Discula theae-sinensis infection within 12 h after inoculation. The error bars indicate the standard deviation (SD) based on three biological replicates. Asterisks (*) denote the level of statistical significance, where * indicates p < 0.05, ** indicates p < 0.01), and ns indicates non-significant. Dts, D. theae-sinensis.