ABSTRACT
Three proteins containing a midasin homologue 1 (MDN1) domain from the yeast Solanum chacoense and Arabidopsis thaliana have important functions in yeast survival, seed development, and female gametogenesis. In this study, a novel protein containing the MDN1 domain from Arabidopsis negatively regulated abscisic acid (ABA) signalling during seed germination. Seeds of a T-DNA insertion line of this gene exhibited increased sensitivity to ABA during seed germination and seedling development (named sag). By contrast, seeds with overexpressed AtSAG (OX2) were less sensitive to ABA. The seeds of the sag mutant showed similar sensitivity to high concentrations of mannitol and NaCl during these stages. AtSAG was also highly expressed in germinating seeds. However, ABA-induced AtSAG expression remained almost unchanged. ABA-responsive marker genes, including ABI3, ABI5, Em1, Em6, RD29A, and RAB18, were upregulated in sag mutants but were downregulated in OX2. Genetic analyses indicated that the function of AtSAG in ABA signalling depended on ABI3 and ABI5. The expression of some target genes of ABI3 and ABI5, such as seed storage protein and oleosin genes, was induced higher by ABA in sag mutants than in wild-type germinated seeds, even higher than in abi5 mutants. This finding indicated that other regulators similar to ABI3 or ABI5 played a role during these stages. Taken together, these results indicate that AtSAG is an important negative regulator of ABA signalling during seed germination and seedling development.
Subject(s)
Abscisic Acid/pharmacology , Arabidopsis Proteins/genetics , Arabidopsis/genetics , Gene Expression Regulation, Plant , Plant Growth Regulators/pharmacology , Signal Transduction , Arabidopsis/growth & development , Arabidopsis/physiology , Arabidopsis Proteins/metabolism , Basic-Leucine Zipper Transcription Factors/genetics , Basic-Leucine Zipper Transcription Factors/metabolism , Down-Regulation , Gene Expression , Germination , Mannitol/pharmacology , Mutagenesis, Insertional , Plants, Genetically Modified , Protein Structure, Tertiary , Seedlings/genetics , Seedlings/growth & development , Seedlings/physiology , Seeds/genetics , Seeds/growth & development , Seeds/physiology , Sodium Chloride/pharmacology , Transcription Factors/genetics , Transcription Factors/metabolism , Up-RegulationABSTRACT
To characterize the microRNAs that contribute to the development of brace root, Solexa high-throughput sequencing of three libraries derived from tissues of node (N), nodes with just-emerged brace roots (NR), and nodes with just-emerged brace roots after IAA treatment (NRI) was performed. Total 650,793, 957,303 and 1,082,948 genome-matched unique reads were obtained in N, NR and NRI libraries, respectively. Further analysis confirmed the authenticity of 137 known miRNAs and the discovery of 159 novel miRNAs in maize. 14 conserved and 16 novel miRNAs differentially expressed in brace root, as well as 15 target genes, were identified and validated by qRT-PCR during maize brace root development. Moreover, we identified 9 miRNA precursor-matched novel sRNAs that may form miRNA clusters, as well as 24 nt siRNAs in the three libraries. In addition, we suggest that auxin represent a regulator in brace root development and can be regulated at the posttranscriptional level by miRNAs.
