Red and far-red light contrastingly influence storage root development and gene expression profile in radish (Raphanus sativus L.)
摘要
The storage root is a specialized underground organ of biennial and perennial plants. In most root crops, the modification of roots for nutrient storage has a strictly defined seasonality and is regulated by environmental cues such as photoperiod and light quality. Here, we show that red light (660 nm, R660) and far-red light (730 nm, FR730) have opposite effects on storage root formation, flowering and gene expression profiles in radish (Raphanus sativus L.). The R660 caused taproot thickening and the formation of a storage root, attenuating the flowering, while FR730 negatively affected the development of the storage root, stimulating flowering. Taproots of radish plants grown under R660 demonstrated extensive proliferation in the cambium and xylem parenchyma cells, while in the taproots of plants grown on FR730 xylem parenchyma was largely transformed into sclerenchyma. Radish plants cultivated under R660 light accumulated more water-soluble sugar and starch in their taproots than those under FR730. Transcriptome analysis allowed to identify new genes involved in light quality-dependent regulation of taproot development. R660 caused downregulation of key ‘flowering genes’ such as CONSTANS-LIKE, FT, SOC1, etc. in both leaves and roots of radish. At the same time, several key regulators of root development, such as WOX11, WOX5, LBD3 and SCR, were specifically upregulated in the taproots on R660. Numerous genes involved in sucrose metabolism and phytohormonal balance also demonstrated contrasting expression patterns under R660 and FR730. Changes in the expression of these genes may underlie the transition to storage root formation or flowering in response to R660 and FR730, correspondingly. Our results suggest a molecular basis for the red light-dependent stimulation of storage root growth.