Effect of photoperiod on the formation of cherry radish root

Radish root formation under short photoperiod is a common sense, however, cherry radish is a kind of four-season radish and the relation of photoperiod and cherry radish root formation is not clear until now. Effect of different photoperiods (8 h/16 h, 12 h/12 h, and 16 h/8 h) on the development and antioxidant ability of cherry radish as well as expression of relative genes was investigated in this study. Surprisingly, the most robust radish plant and largest biomass were found at the long photoperiod regime (16h/8 h), even though both the polyphenol content and antioxidant ability in terms of DPPH and FRAP were lower than those in 12/12 h photoperiod. Moreover, under 16h/8h photoperiod it can form the radish product organs in 30 d but not for the others. Gene expression analysis showed that eight non-coding miRNAs and coding RNAs were both involved in the regulation of radish root formation. MiR160, miR165, and miR396 were up-regulated by 16h/8 h photoperiod treatment while miR156 and miR157 were down-regulated. The up-regulation of miR160 and the opposite expression trend of ARF16 indicated that miR160 may mediate the light-respond root formation by targeting ARF16. An auxin response factor ARF6 and a cell wall structure related WRKY2 were also significantly up-regulated by the longer illumination treatment compared with the control. Thus, unlike other radish roots that form in short-day condition, the cherry radish roots grow fastest in long photoperiod and miR160-ARF16 are involved in the quick formation of cherry radish root.