Sugar beet (Beta vulgaris) is the world’s second-most important crop for sugar production, trailing only behind sugarcane. While significant advances in breeding have increased sugar content from 4% to 20% over the past century, further progress has been hindered by genetic and environmental limitations. The current bottleneck in sugar beet production underscores the urgent need for a deeper understanding of the genetic mechanisms that govern key agronomic traits such as biomass and sugar content. With global sugar demand on the rise, researchers are now more focused than ever on unraveling the genetic foundation of sugar beet productivity to develop high-yield varieties.

A team of researchers from the Inner Mongolia Academy of Science and Technology recently published a study (DOI: 10.1093/hr/uhae230) in Horticulture Research on August 12, 2024, that investigates the genetic factors underlying crucial agronomic traits in sugar beet. By leveraging genome-wide association studies (GWAS) and RNA sequencing, the study aims to pinpoint the genes responsible for improving sugar beet yields and sugar content.

The research involved an extensive collection of 269 sugar beet accessions from around the world. Researchers measured 12 phenotypic traits, including biomass and soluble sugar content, and re-sequenced the genomes of 207 accessions, uncovering over 14 million SNPs and nearly 3 million indels. This revealed a remarkable genetic diversity among the various accessions. Through GWAS and RNA sequencing, the team identified several key genes linked to phenotypic variations in sugar beet. Notably, they discovered UDP-glucose 4-epimerase, a dual-role gene that regulates both sugar accumulation and cell wall synthesis. This gene demonstrated distinct expression patterns at different stages of development, suggesting it plays a pivotal role in managing sugar distribution within the plant. Furthermore, the study revealed significant genetic differences between Chinese and non-Chinese sugar beet accessions, offering valuable insights into breeding history and genetic divergence. These findings lay the groundwork for molecular breeding in sugar beet, providing tools to improve yields and sugar content in future varieties.

Proposed model of UDP-glucose 4-epimerase regulating sugar distribution

Genes in red font are upregulated genes in high sugar accessions identified from RNA-seq. The gene in green font is the upregulated one in high biomass accessions identified from GWAS and validated by qRT–PCR. During the early growth stage of sugar beet, UDP-glucose 4-epimerase (transcript 104892324) showed high expression, resulting in increased glucose production. Concurrently, high fructose hydrolase expression generated higher fructose levels, which, together with glucose, promoted sucrose synthesis. At the late developmental stage, the transcript (ID 104892143) showed high expression and facilitated the conversion of UDP-glucose into UDP-galactose, providing raw materials for cell wall polysaccharide synthesis. These two enzymes work as switches that dynamically regulate sugar distribution.

Dr. Zhimin Yang, one of the corresponding authors of the study, commented, “Our findings provide a solid foundation for molecular breeding in sugar beet. By pinpointing key genes like UDP-glucose 4-epimerase, we now have the ability to target specific genetic markers to develop sugar beet varieties with higher yields and enhanced sugar content.”

The implications of this study are far-reaching for the sugar beet industry. By identifying genes that regulate key traits such as biomass and sugar accumulation, breeders now have the potential to develop new varieties that offer both improved yields and higher sugar content. This research not only deepens our understanding of sugar beet genetics but also provides practical tools for molecular breeding, potentially leading to more efficient, sustainable, and productive sugar production in the future.

Source – Newswise