# The Root Development Genes (RDGs) Network in Brassica napus and the Role of BnaSHR-6 in Response to Low Nitrogen

## TL;DR

This study identifies root development genes in Brassica napus and shows how BnaSHR-6 helps the plant adapt to low nitrogen conditions.

## Contribution

The study introduces a comprehensive network of root development genes in B. napus and highlights the role of BnaSHR-6 in low nitrogen response.

## Key findings

- 218 root development genes (RDGs) were identified in Brassica napus through homology-based retrieval.
- BnaSHR-6 regulates primary and lateral root growth under low nitrogen conditions and enhances resistance.
- Low nitrogen induced significant changes in RDG expression, with over 50% of genes differentially expressed.

## Abstract

The root system is vital for Brassica napus water/nutrient uptake and anchorage, highlighting the importance of identifying root development genes (RDGs). In this study, we identified 218 RDGs in B. napus through homology-based retrieval. Phylogenetic analysis of 22 representative species revealed that the RDGs are widely present in plants ranging from aquatic algae to angiosperms. RDGs in B. napus expanded through whole-genome duplication (WGD) events between Brassica rapa and Brassica oleracea ancestors and smaller duplications specific to B. napus. Promoter analysis identified 115 cis-elements, mainly abiotic stress-related and light-responsive. Transcription factor networks showed regulation by BBR-BPC, MIKC_MADS, AP2, and GRAS families. Transcriptome analysis under multiple stresses revealed that low nitrogen (LN) induced the most pronounced changes, with >50% (109/218) of RDGs differentially expressed in roots. Furthermore, we screened the BnaSHR-6 gene, which is co-localized in both primary roots (PR) and lateral roots (LR), and responds strongly to LN. Phenotypic analysis revealed that the BnaSHR-6 gene regulates the growth and development of both PR and LR under LN conditions, and confers a degree of resistance. These findings advance our understanding of RDGs in B. napus and provide valuable gene resources for subsequent molecular breeding.