RNA-Seq reveals that sucrose-free medium improves the growth of potato (Solanum tuberosum L.) plantlets cultured in vitro

Abstract

In the present study, the differentially expressed genes (DEGs), morphological and physiological parameters, leaf anatomical structures and chloroplast ultrastructures of potato (Solanum tuberosum L.) plantlets cultured in vitro on medium with or without sucrose were analyzed. In total, 3814 DEGs (2037 upregulated and 1777 downregulated genes) were identified in potato plantlets cultured on sucrose-free medium (S0 treatment) in comparison to potato plantlets cultured on sucrose-added medium (S treatment, used as the control). Robust plantlets in the S0 treatment were observed, with an increase in biomass accumulation, stem diameter and health index. In addition, greater chlorophyll fluorescence indicators, photochemical quantum yield (φPSII), the ratio of variable fluorescence to the maximum fluorescence (Fv/Fm), apparent electron transfer rate (ETR) and photochemical quenching (qp), were also detected in the S0 treatment, which might be associated with the abundant expression of DEGs in the metabolic pathways “photosynthesis”, “photosynthesis-antenna proteins” and “carbon fixation in photosynthetic organisms”. Regularly arranged epidermis and spongy and palisade parenchyma were observed in the leaves of potato plantlets in the S0 treatment in conjunction with an increase in the expression of many DEGs involved in “leaf anatomical structure development” and “leaf anatomical structure arrangement”. Well-developed chloroplasts with complete inner membrane systems in potato plantlets in the S0 treatment were associated with the upregulation of most DEGs enriched in gene ontology (GO) terms involved in the development of chloroplast and chloroplast inner membrane systems. In conclusion, sucrose-free medium improved the growth, leaf anatomy formation and chloroplast ultrastructure development of potato plantlets cultured in vitro. Our results provide new insights into understanding the effects of sucrose-added and sucrose-free media on the growth and development of potato plantlets and may help to improve the micropropagation of potato plantlets cultured in vitro at the genetic level. The sucrose-free medium facilitated potato plantlets growth and might trigger better photosynthetic capability via strengthening “photosynthesis” metabolic pathway and increasing chlorophyll fluorescence Fv/Fm, φPSIIqp and ETR in potato plantlet.