Lignocellulosic fibers in leaves and stems of Brassica juncea: Natural variation, functional differentiation and allocation mechanisms

Lignocellulosic fibers, comprising cellulose, hemicellulose, and lignin, are the predominant structural carbohydrates found in the cell wall and secondary cell wall of plants. These fibers play a crucial role in maintaining the cell wall stability, providing mechanical strength and rigidity to plant organs, and serving as alternative energy sources. However, the natural variation, functional differentiation, and allocation mechanisms of lignocellulosic fibers in Brassica juncea remain unclear. This research investigated the levels of cellulose, hemicellulose, lignin and lignocellulosic fibers in the leaves and stems of 200 Brassica juncea germplasm lines at two distinct locations. The significant variation in lignocellulosic contents enabled the identification of two lines suitable for energy source crops and five lines suitable for vegetable and animal feed purposes. Moreover, the lignocellulosic contents exhibited a positive correlation with lodging resistance, vascular density, and Sclerotinia sclerotiorum resistance. Discrepancies in the composition and quantities of lignocellulosic fibres were noted between leaves and stems. To study the mechanism underling the differential allocation of lignocellulosic contents between stems and leaves, despite sharing the same synthesis pathway, four lines were selected for RNA-Sequencing analysis. By integrating differentially expressed gene (DEG), weighted correlation network analysis (WGCNA), and functional analysis, eleven hub genes were identified. Among these candidate genes, the function of BjuA043659 was analyzed. The study provides valuable insights into understanding the mechanism of lignocellulose differential allocation and tissue function differentiation between leaves and stems, as well as for genetic improvement specifically for leaves and stems of B. juncea . The lignocellulose content in stems is significantly higher than that in leaves in B. juncea . As the lignocellulose content increases in both stems and leaves, the resistance to Sclerotinia sclerotiorum also increases. Additionally, the increase in lignocellulose content in stems enhances lodging resistance. • Brassica juncea has a potential as an energy crop. • Eleven hub genes for the differential distribution of lignocellulose between leaves and stems were identified. • The lignocellulose content correlates positively with lodging and Sclerotinia sclerotiorum resistance.