RsCLE22a Regulates the Taproot Growth through Auxin Signaling-related Pathway in Radish (Raphanus sativus L.).

CLAVATA3/EMBRYO SURROUNDING REGION-related (CLE) peptides are a class of small polypeptide molecules involved in plant growth and development. Although radish is an important root vegetable crop worldwide, the functions of CLE peptides in taproot formation remain elusive. Here, a total of 48 RsCLE genes were identified from the radish genome. RNA in situ hybridization showed that RsCLE22a gene was highly expressed in the vascular cambium. Overexpression of RsCLE22a inhibited root growth by impairing stem cell proliferation in Arabidopsis, and exogenous supplement of RsCLE22 peptide (CLE22p) was shown the similar phenotypes in radish. The vascular cambial activity was increased in RsCLE22a-silenced plants. Transcriptome analysis revealed that CLE22p altered the expression of several genes involved in meristem development and hormone signal transduction in radish. Immunolocalization results showed that CLE22p increased auxin accumulation in vascular cambium. Yeast one-hybrid (Y1H) and dual-luciferase assay (DLA) showed that the RsWOX4 (WUSCHEL-RELATED HOMEOBOX 4) gene binds to RsCLE22a promoter and activated its transcription. Meanwhile, the expression level of RsWOX4 was related to vascular cambial activity and regulated by auxin. Furthermore, a RsCLE22a-RsWOX4 module was proposed to regulate taproot vascular cambium activity through auxin signaling-related pathway in radish. These findings provided novel insight into the regulation of root growth in horticultural crops.