An efficient method for tissue-specific protoplast isolation suitable for single-cell RNA sequencing and transient gene expression analysis in saffron (Crocus sativus L.).

Abstract

Background: Protoplasts have been widely utilized in tissue culture, single-cell RNA sequencing, and transient gene expression analyses. However, the primary challenge in their preparation lies in the efficient removal of rigid cell walls to obtain high-quality plant cells. The aim of this study is to establish an effective method for protoplast isolation from saffron (Crocus sativus L.), thereby accelerating advances in molecular biology research in this species.

Result: Tissue-specific protoplasts were successfully isolated from apical buds, petals, leaves, and roots of saffron, with yields of approximately 8.81 × 10⁶, 1.36 × 10⁷, 7.84 × 10⁵, and 5.69 × 10⁵/g FW, and viabilities of ~ 95%, ~ 94%, ~ 96%, and ~ 61%, respectively. The optimal enzymatic digestion conditions varied by tissue type: apical buds (0.6 M D-mannitol, 1.5% cellulase, 0.5% macerozyme, 28 °C, 3 h); roots (0.7 M D-mannitol, 2.0% cellulase, 0.5% macerozyme, 0.5% pectinase, 28 °C, 4 h); petals (0.7 M D-mannitol, 1.5% cellulase, 0.5% macerozyme, 28 °C, 3.5 h); and mesophyll (0.7 M D-mannitol, 1.5% cellulase, 0.5% macerozyme, 28 °C, 4 h). The quality of the protoplasts was affected by developmental stages and sampling locations. Furthermore, two high-quality single-cell libraries were constructed using protoplasts from non-flowering and flowering apical buds, respectively. We successfully visualized the subcellular localization of GFP in the mesophyll protoplasts.

Conclusion: This study presents the first detailed report on protoplast isolation, evaluation, and application in saffron. By overcoming the technical challenges of tissue-specific protoplast isolation from diverse organs, we established a highly efficient method that enables both the development of novel germplasm and mechanistic insights into saffron organogenesis, growth, and development.