Brassica rapa orphan genes largely affect soluble sugar metabolism

Abstract

Orphan genes (OGs), which are genes unique to a specific taxon, play a vital role in primary metabolism. However, little is known about the functional significance of Brassica rapa OGs (BrOGs) that were identified in our previous study. To study their biological functions, we developed a BrOG overexpression (BrOGOE) mutant library of 43 genes in Arabidopsis thaliana and assessed the phenotypic variation of the plants. We found that 19 of the 43 BrOGOE mutants displayed a mutant phenotype and 42 showed a variable soluble sugar content. One mutant, BrOG1OE, with significantly elevated fructose, glucose, and total sugar contents but a reduced sucrose content, was selected for in-depth analysis. BrOG1OE showed reduced expression and activity of the Arabidopsis sucrose synthase gene (AtSUS); however, the activity of invertase was unchanged. In contrast, silencing of two copies of BrOG1 in B. rapa, BraA08002322 (BrOG1A) and BraSca000221 (BrOG1B), by the use of an efficient CRISPR/Cas9 system of Chinese cabbage (B. rapa ssp. campestris) resulted in decreased fructose, glucose, and total soluble sugar contents because of the upregulation of BrSUS1b, BrSUS3, and, specifically, the BrSUS5 gene in the edited BrOG1 transgenic line. In addition, we observed increased sucrose content and SUS activity in the BrOG1 mutants, with the activity of invertase remaining unchanged. Thus, BrOG1 probably affected soluble sugar metabolism in a SUS-dependent manner. This is the first report investigating the function of BrOGs with respect to soluble sugar metabolism and reinforced the idea that OGs are a valuable resource for nutrient metabolism.

Comparative Metabolic Study of Two Contrasting Chinese Cabbage Genotypes under Mild and Severe Drought Stress

“…Soluble sugars mainly include sucrose and its products glucose and fructose [ 34 ]. It was found that drought increased the amount of soluble sugar in Chinese cabbage [ 35 ].…”

Taxonomically Restricted Genes are Associated with Responses to Biotic and Abiotic Stresses in Sugarcane (Saccharum spp.)

“…The QQS gene, an Arabidopsis gene involved in carbon and nitrogen allocation, was introduced into the soybean genome and increased starch and protein levels in the leaves (Li and Wurtele, 2015; Li et al, 2015; O’Conner et al, 2018). OGs were also validated via gene editing as vital for soluble sugar metabolism in brassicas (Jiang et al, 2020).…”

“…In Arabidopsis, the well-studied OG QQS ( Qua-Quine Starch ) is involved in the regulation of nitrogen allocation, and when QQS is transferred and expressed in other species, it affects important traits such as protein content, consequently increasing crop yields (O’Conner et al, 2018). Previous works also reported that OGs play a vital role in soluble sugar metabolism in Brassica rapa based on an in-depth analysis of orphan genes by establishing a gene editing system and phenotypic validation (Jiang et al, 2020).…”

CRISPR/Cas9-Mediated Gene Editing Revolutionizes the Improvement of Horticulture Food Crops

“…The knockout of ORs led to reduced fructose and glucose contents. 86 The carrot Flavanone-3-hydroxylase (F3H) gene acted as a reporter for blockage of the anthocyanin biosynthesis in a model purple-colored callus. Knocking out F3H through CRISPR/Cas9 led to the discoloration of calli, validating its role in carrot anthocyanin synthesis.…”

“…Two orphan genes, OR1A and OR1B , were identified as regulators in soluble sugar metabolism. The knockout of ORs led to reduced fructose and glucose contents . The carrot Flavanone-3-hydroxylase ( F3H ) gene acted as a reporter for blockage of the anthocyanin biosynthesis in a model purple-colored callus.…”