# Genome wide identification of serotonin N-acetyltransferase (PbSNAT) gene family and their role in pear (Pyrus bretschneideri) fruit development

## TL;DR

This paper identifies and analyzes the serotonin N-acetyltransferase gene family in pear, linking it to fruit development and melatonin biosynthesis.

## Contribution

The first comprehensive characterization of the PbSNAT gene family in Pyrus bretschneideri and its role in fruit development.

## Key findings

- 51 PbSNAT genes were identified and classified into six clades with conserved structures and functions.
- PbSNAT1 and PbSNAT46 are strongly expressed during fruit development and correlate with melatonin abundance.
- Tissue-specific expression patterns suggest roles in organ development and stress responses.

## Abstract

Serotonin N-acetyltransferase (SNAT) is a key enzyme catalyzing a critical step in phytomelatonin biosynthesis, which plays important roles in plant growth and stress responses. However, the SNAT gene family has not been systematically characterized in Pyrus bretschneideri, an economically important pear species. This study aims to fill this gap by conducting a comprehensive analysis of the PbSNAT gene family and exploring its functional implications.

A genome-wide identification of PbSNAT genes was performed in P. bretschneideri. Phylogenetic analysis was used to classify PbSNAT proteins into distinct clades. Physicochemical properties, motif compositions, and gene structures of PbSNATs were analyzed to evaluate their conservation. Promoter and Gene Ontology (GO) analyses were conducted to predict their regulatory mechanisms and functional roles. Expression profiling of PbSNAT genes was carried out across different tissues and fruit developmental stages of five pear cultivars to investigate their expression patterns. Additionally, the correlation between SNAT expression, melatonin (MT) abundance, and fruit development was analyzed.

A total of 51 PbSNAT genes (PbSNAT1–51) were identified from the pear genome. Phylogenetic analysis grouped these PbSNAT proteins into six clades. Most PbSNATs are hydrophobic and localized in chloroplasts. Motif and gene structure analyses revealed high conservation within each clade, supporting the phylogenetic classification. Promoter and GO analyses indicated that PbSNAT genes are responsive to stress and involved in chloroplast development and indole acetic acid metabolism. Expression profiling showed tissue-specific expression patterns of PbSNAT genes, suggesting their roles in organ development. Furthermore, PbSNAT genes are widely expressed across five pear cultivars at different fruit developmental stages. PbSNAT1 was strongly expressed during fruit development, implying its role in fruit setting and ripening. High abundances of SNAT and MT were detected in pericarp and pulp tissues, and their levels were correlated with PbSNAT46 expression.

This study provides the first comprehensive characterization of the PbSNAT gene family in P. bretschneideri. The conservation of sequence, structure, and expression patterns of PbSNATs suggests their conserved and divergent functional roles. The tissue-specific and fruit development-associated expression of PbSNAT genes, along with their correlation with MT abundance, indicates that they play crucial roles in pear growth and fruit development. Particularly, PbSNAT1 and PbSNAT46 may be key regulators of fruit setting, ripening, and MT biosynthesis in pear. These findings establish a valuable foundation for future functional studies and molecular breeding of pear.