# Regulatory Mechanisms of Total Soluble Solids in Tomato: From QTL Mapping to Gene Editing

## TL;DR

This paper reviews how genetic and environmental factors regulate tomato fruit quality, focusing on total soluble solids and strategies to improve them.

## Contribution

The paper integrates recent advances in genomics and gene editing to propose new strategies for improving tomato fruit quality.

## Key findings

- QTLs like Lin5 and SlALMT9 have been identified as key regulators of tomato TSS.
- CRISPR/Cas9 has enabled functional characterization of genes affecting sugars and acids in tomatoes.
- Environmental factors significantly influence TSS, requiring optimized cultivation practices.

## Abstract

Total Soluble Solids (TSS) in tomatoes is a core indicator for evaluating fruit quality and processing characteristics. Its composition mainly consists of soluble sugars (such as fructose and glucose) and organic acids (such as citric acid and malic acid). The contents of sugars and acids and their ratio directly affect the flavor and nutritional value. Cultivated tomatoes have a TSS of 4–6%, compared with 10–15% in wild varieties. In recent years, with the advancement of molecular biology and genomics technologies, significant progress has been made in the research on the regulatory mechanisms of tomato fruit TSS and major sugars and acids, including the identification of major quantitative trait locus (QTLs) (Lin5, SlALMT9), functional characterization via CRISPR/Cas9 and elucidation of the transporter network. Breaking the negative correlation between TSS and yield remains a major bottleneck in breeding. Analyzing the mechanism by which environmental factors regulate the TSS and optimizing cultivation measures are crucial for increasing the TSS content in tomatoes. The deep integration of cutting-edge technologies (such as Genome-wide association studies (GWAS), metabolome-wide association studies (mGWAS), Genomic selection (GS), genome editing, and crop modeling) with design breeding is expected to accelerate the development of high-TSS tomato varieties. This paper reviews the current research status from the following four aspects: QTL mapping related to tomato TSS and mining of major genes, metabolic and transport mechanisms of major sugars and acids and key genes, the influence of environmental factors on TSS, and application of genetic improvement strategies and technologies.