Cloning and Functional Analysis of BraTSD2 Associated with Root Swelling in Turnip (Brassica rapa L.)

Turnip, a subspecies of Brassica rapa, is one of the important root vegetable crops in China. Its roots, as significant product organs, possess values for consumption, feed, and medicinal purposes. A previous study localized a gene associated with root swelling traits. In this study, we cloned the turnip root swelling-related gene BraTSD2 (TUMOROUS SHOOT DEVELOPMENT 2) and performed a preliminary functional analysis. The bioinformatics analysis of BraTSD2 indicated that the protein is likely to possess a transmembrane feature. Additionally, predictions of its secondary and tertiary structures suggested that BraTSD2 shares similarities with the structure of a pectin methyltransferase. Temporal and spatial expression analysis of BraTSD2 using qPCR techniques indicated that the BraTSD2 gene had the highest expression levels in roots and hypocotyls during the swelling stage. Analysis of the promoter cis-acting elements of the BraTSD2 gene revealed that the promoter is regulated by signals associated with light response, abscisic acid, stress, salicylic acid, and MYBHI. The promoter of the turnip BraTSD2 gene was expressed throughout the whole plant in Arabidopsis thaliana. Phenotypic observation and analysis of A. thaliana overexpression BraTSD2 transgenic lines showed that plants overexpressing BraTSD2 had fewer primary and lateral roots compared to the wild type, with lighter leaf color, and delayed development and flowering. A previously reported protein CGR3, associated with pectin methyltransferase function, interacts with protein BraTSD2. When the BraTSD2 gene is overexpressed in A. thaliana, it can affect root morphology, which may be the basic structural condition for the generation of turnip root swelling traits.