Isolation and Characterization of a Novel Drought Responsive Gene Encoding a Glycine-rich RNA-binding Protein in Malus prunifolia (Willd.) Borkh.

Drought is one of the most severe environmental factors that impair plant growth and agricultural production. To investigate how Malus prunifolia, an excellent apple rootstock with strong drought tolerance, adapts to stress and to identify genes for improving this important trait, we constructed a suppression subtractive hybridization cDNA library from seedling leaves under water stress. The cDNA for a drought-inducible glycine-rich RNA-binding protein (GR-RBP) was isolated, and the gene was characterized for its role in the response of Malus seedlings to drought stress. cDNA clone MpGR-RBP1 has 781 nucleotides, with an open reading frame of 516 nucleotides. The deduced 171 amino acids contain an amino-terminal RNA recognition motif and a carboxyl-terminal glycine-rich domain, with structural similarity to a class of stress-induced GR-RBP proteins found in other plants. Phylogenetic analysis confirmed that the MpGR-RBP1 protein belongs to the plant GR-RBP family, members of which play important roles in posttranscriptional regulation of gene expression under various stress conditions. The expression profile of MpGR-RBP1 transcripts was detected by quantitative real-time polymerase chain reaction (PCR) and semiquantitative reverse transcriptase PCR. MpGR-RBP1 was expressed in both roots and leaves, with expression being higher in the latter. This is the first report of this class of protein in Malus plants, and the putative role of MpGR-RBP1 is discussed.