Zinc deficiency-induced defensin-like proteins are involved in the regulation of root growth in Arabidopsis.

The depletion of cellular zinc (Zn) adversely affects plant growth. Plants have adaptation mechanisms to Zn-deficient conditions by using regulators, including transcription factors and metal transporters. We previously identified three defensin-like (DEFL) proteins (DEFL203, DEFL206, and DEFL208) that were induced in Arabidopsis thaliana roots under Zn-depleted conditions. DEFLs are small cysteine-rich peptides involved in defense responses, development, and excess metal stress in plants. However, the functions of DEFL in the Zn-deficiency response are largely unknown. Here, phylogenetic tree analysis revealed that seven DEFLs (DEFL202-208) were categorized into one subgroup. Among the seven DEFLs, the transcripts of five (except for DEFL204 and DEFL205) were upregulated by Zn deficiency, consistent with the presence of cis-elements for the basic-region leucine-zipper 19 (bZIP19)/bZIP23 in their promoter regions. Microscopic observation of GFP-tagged DEFL203 showed that DEFL203-sGFP was localized to the apoplast and plasma membrane. While a single mutation of the DEFL202 or DEFL203 gene only slightly affected root growth, defl202 defl203 double mutants showed enhanced root growth under all growth conditions. We also showed that the size of the root meristem was increased in the double mutants compared to the wild type. Our results suggest that DEFL202 and DEFL203 are redundantly involved in the negative regulation of root growth under Zn deficient conditions through a reduction in the length and cell number of the root meristem.