Cell wall composition and transcriptomics in stem tissues of stinging nettle (Urtica dioica L.): Spotlight on a neglected fibre crop

Stinging nettle (Urtica dioica L.) produces silky cellulosic fibres, as well as bioactive molecules. To improve the knowledge on nettle and enhance its opportunities of exploitation, a draft transcriptome of the "clone 13" (a fibre clone) is here presented. The transcriptome of whole internodes sampled at the top and middle of the stem is then compared with the core and cortical tissues sampled at the bottom. Young internodes show an enrichment in genes involved in the biosynthesis of phytohormones (auxins and jasmonic acid) and secondary metabolites (flavonoids). The core of internodes collected at the bottom of the stem is enriched in genes partaking in different aspects of secondary cell wall formation (cellulose, hemicellulose, lignin biosynthesis), while the cortical tissues reveal the presence of a C starvation signal probably due to the UDP-glucose demand necessary for the thickening phase of bast fibres. Cell wall analysis indicates a difference in rhamnogalacturonan structure/composition of mature bast fibres, as evidenced by the higher levels of galactose measured, as well as the occurrence of more water-soluble pectins in elongating internodes. The targeted quantification of phenolics shows that the middle internode and the cortical tissues at the bottom have higher contents than top internodes. Ultrastructural analyses reveal the presence of a gelatinous layer in bast fibres with a lamellar structure. The data presented will be an important resource and reference for future molecular studies on a neglected fibre crop.