Characterization of Rice Group 3 LEA Genes in Developmental Stages and Under Abiotic Stress

We performed a BLAST search of the rice database and screened four group 3 late embryogenesis abundant genes (OsG3LEA-47.3, OsG3LEA-41.9, OsG3LEA-20.5, and OsG3LEA-24.5) that shared characteristics of canonical G3LEAs such as multiple copies of consensus motif, hydrophilic, structural intrinsic disorder, thermostability, abscisic acid (ABA)-responsiveness, and high G and C content in gene sequence. Under nonstress conditions, OsG3LEA-20.5 and OsG3LEA-24.5 were constitutively expressed, whereas OsG3LEA-47.3 and OsG3LEA-41.9 were expressed in a stage- or tissue-specific manner. Transcripts of OsG3LEA-20.5 and OsG3LEA-24.5 accumulated under salt, ABA, and cold stress treatment. By contrast, OsG3LEA-47.3 and OsG3LEA-41.9 showed less responsiveness to stress in tillering and heading stages, respectively. All genes showed enhanced transcript levels after pollination and embryo development. To investigate the functions, we overexpressed OsG3LEA-47.3, OsG3LEA-41.9, OsG3LEA-20.5, and OsG3LEA-24.5 in Arabidopsis (47.3-ox, 41.9-ox, 20.5-ox, and 24.5-ox). Analysis of tolerance to drought stress revealed higher recovery after 14 days of dehydration treatment for 47.3-ox or 41.9-ox than the wild type (WT), 20.5-ox, or 24.5-ox. In addition, 47.3-ox and 24.5-ox plants showed higher survival than WT, 41.9-ox, and 20.5-ox plants under heat treatment, which induced similar expression patterns of heat shock protein genes in WT, 47.3-ox, 41.9-ox, 20.5-ox, and 24.5-ox plants. In vitro chaperone activity with the model substrate citrate synthase was comparable between OsG3LEA-47.3 and OsHSP16.9A, a rice molecular chaperone providing thermoprotection in vivo and in vitro. These results suggest that rice G3LEAs share many physical and biological features but function in contrasting ways.