Functional characterization of TONSOKU in Cyathula officinalis reveals its role in DNA damage and root development

Cyathula officinalis Kuan. (C. officinalis), a perennial medicinal herb endemic to Sichuan, holds significant pharmacological value in traditional medicine, yet its key functional genes governing physiological traits remain unexplored.

CoTSK encodes a nuclear protein containing conserved tetratricopeptide repeat (TPR) and leucine-rich repeat (LRR) domains that phylogenetically clusters with Amaranthaceae homologs. Subcellular localization confirmed its nuclear distribution, consistent with a role in genome maintenance. Functional assays demonstrated that CoTSK expression conferred a 2.5-fold survival advantage under 0.02% methyl methanesulfonate (MMS) stress in E. coli, while showing no tolerance to hydroxyurea (HU), indicating specific protection against alkylation-induced DNA damage. Tissue-specific expression profiling revealed distinct stem-predominant expression in C. officinalis, diverging from the leaf-biased pattern observed in C. capitata (CcTSK). Overexpression of CoTSK partially rescued root developmental defects in Arabidopsis AtTSK mutants, restoring root length to 30-42% of wild-type levels, though stem flattening and rosette proliferation phenotypes remained unrescued.

These findings establish that nuclear-localized CoTSK maintains conserved functions in root development and DNA damage repair while exhibiting distinct stem-predominant expression patterns divergent from its paralog CcTSK. This functional elucidation identifies CoTSK as a molecular target for genetic enhancement of medicinal biomass, particularly through modulation of stem-root developmental coordination, and provides evolutionary insights into TSK family differentiation in Amaranthaceae species.