Regulation of root expansion by cytokinin via RsRR11 of cherry radish

• Stele is the main enlarged part of the fleshy root. • Cytokinin regulates the expansion of fleshy roots. • RsRR11 negatively regulates fleshy root expansion. Radish is one of the important cultivated crops in the world, and fleshy root expansion is a critical stage in the growth and development of radish, but its regulatory mechanism is not clear. In the present study, the cortex and stele of cherry radish roots were sectioned and observed, and 12 d, 16 d, and 20 d were identified as the critical periods for stele expansion. The determination of endogenous cytokinin content revealed that stele expansion was positively correlated with changes in endogenous cytokinin content. Analysis of the expression pattern of genes related to cytokinin signaling pathway showed that RsRR11s were specifically expressed in the stele and changed with the root expansion. Upon exogenous 6-BA treatment, the expansion rate of the stele of cherry radish increased while the expression of RsRR11–1 / 11–2 was suppressed. Further analysis of rsrr11–1 and rsrr11–2 mutant plants revealed that mutation of RsRR11 promoted the expansion of fleshy root, indicating that RsRR11 negatively regulates fleshy root expansion in cherry radish. In conclusion, we have demonstrated that the stele is the main enlarged part of radish and RsRR11 in cytokinin pathway negelatively regulated the enlargement of radish stele, which lay foundation for the regualtion of fleshy root.