Transcriptome analysis of fiber development under high-temperature stress in flax (Linum usitatissimum L.)

In recent years, frequent extreme climates (including high temperatures) have increasingly threatened the production of crops. Flax is a crop suitable for growing in a cool environment, and its fiber formation is greatly affected by temperature. However, the understanding of the regulatory effect of high-temperature (HT) stress on fiber development at the RNA level is limited. In this study, we selected three developmental stages of flax fiber (fiber elongation stage, fiber cell thickening stage, and fiber maturity stage), combined with second-generation and 3rd-generation transcriptome sequencing, to explore how HT (30 ℃) stress affects the development of flax fiber at the molecular level. The number of differentially expressed genes (DEGs) of the bast in the fiber elongation stage, fiber cell thickening stage, and fiber maturity stage were 2889, 3131, and 5244, respectively. In these three stages, HT had different effects on the development of fiber cells. Through Weight gene co-expression network analysis (WGCNA) and gene co-expression network analysis, hub gene Lus10007349 (XTH) involved in the process of fiber cell expansion and cell wall thickening, and it was sensitive to HT stress and serves as a candidate gene for subsequent research. In addition, we found that under HT stress, the number of fiber cells, cell wall thickness, phloem thickness, and fiber cell area decreased. Determined the chemical composition of the final harvested fiber under HT stress, in which the content of cellulose and acid-soluble lignin was reduced, and the content of pectin was increased. The results of a large number of DEGs sequencing will broaden our understanding of the complex molecular and cellular events in the development of flax phloem fibers affected by HT stress, and lay the foundation for the improvement of flax fibers in the future.