ZmRFP1, the putative ortholog of SDIR1, encodes a RING-H2 E3 ubiquitin ligase and responds to drought stress in an ABA-dependent manner in maize

Abstract

Drought is one of the most important limiting factors in crop production. To identify genes required for the drought stress response in the cereal crop maize, a gene coding for RING-finger protein (ZmRFP1), which is highly responsive to PEG-induced drought stress, was isolated by mRNA differential display and rapid amplification of cDNA ends. The ZmRFP1 encodes a protein of 280 amino acids and contains a single C(3)H(2)C(3)-type RING motif in its C-terminal region. ZmRFP1 is an ortholog of Arabidopsis SDIR1 (salt- and drought-induced RING finger 1) (66% identity to AtSDIR1).The recombinant ZmRFP1 protein purified from Escherichia coli exhibited an in vitro E3 ubiquitin ligase activity. Real-time PCR analysis indicates that the transcript levels of ZmRFP1 were higher in aerial tissues including stems, leaves, tassels and immature ears, and were markedly up-regulated by drought stress, and exogenous ABA, but not by salt, heat and cold stresses. Transient expression of the green fluorescent protein (GFP)-ZmRFP1 fusion protein in onion cells revealed a plasma membrane localization of the protein. Further analysis of ZmRFP1 transcripts between an ABA-deficient transposon mutant viviparous14 (vp14) and its isogenic wild-type line W22 showed that ZmRFP1 transcript levels were induced significantly in the wild-type line under drought stress, but not in the mutant line VP14. These results indicate that ZmRFP1 responds to drought stress in an ABA-dependent way and is likely to function in the ubiquitin conjunction pathway. The ZmRFP1 might serve as a candidate gene in genetic improvement for drought tolerance engineering in cereal crop plants.