RESUMO
Plants remember what they have experienced and are thereby able to confront repeated stresses more promptly and strongly. A subset of the drought responsive genes, called stress memory genes, displayed greatly elevated levels under recurrent drought conditions. To screen for a set of drought stress memory genes in soybean (Glycine max L.), we designed a 180K DNA chip comprising 60-bp probes synthesized in situ to examine 55,589 loci. Through microarray analysis using the DNA chip, we identified 2,162 and 2,385 genes with more than fourfold increases or decreases in transcript levels, respectively, under initial (first) drought stress conditions, when compared with the non-treated control. The transcript levels of the drought-responsive genes returned to basal levels during recovery (watered) states, and 392 and 613 genes displayed more than fourfold elevated or reduced levels, respectively, under subsequent (second) drought conditions, when compared to those observed under the first drought stress conditions. Gene Ontology and MapMan analyses classified the drought-induced memory genes exhibiting elevated levels of transcripts into several functional categories, including those involved in tolerance responses to abiotic stresses, which encode transcription factors, protein phosphatase 2Cs, and late embryogenesis abundant proteins. The drought-repressed memory genes exhibiting reduced levels of transcripts were classified into categories including photosynthesis and primary metabolism. Co-expression network analysis revealed that the soybean drought-induced and -repressed memory genes were equivalent to 172 and 311 Arabidopsis genes, respectively. The soybean drought stress memory genes include genes involved in the dehydration memory responses of Arabidopsis.
RESUMO
AtMYB44 is a member of the R2R3 MYB subgroup 22 transcription factors and regulates diverse cellular responses in Arabidopsis thaliana. We performed quadruple 9-merbased protein binding microarray (PBM) analysis, which revealed that full-size AtMYB44 recognized and bound to the consensus sequence AACnG, where n represents A, G, C or T. The consensus sequence was confirmed by electrophoretic mobility shift assay (EMSA) with a truncated AtMYB44 protein containing the N-terminal side R2R3 domain. This result indicates that the R2R3 domain alone is sufficient to exhibit AtMYB44 binding specificity. The sequence AACnG is the type I binding site for MYB transcription factors, including all members of the subgroup 22. EMSA showed that the R2R3 domain protein binds in vitro to promoters of randomly selected Arabidopsis genes that contain the consensus binding sequence. This implies that AtMYB44 binds to any promoter region that contains the consensus sequence, without determining their functional activity or specificity. The C-terminal side transcriptional activation domain of AtMYB44 contains an asparagine-rich fragment, NINNTTSSRHNHNN (aa 215-228), which, among the members of subgroup 22, is unique to AtMYB44. A transcriptional activation assay in yeast showed that this fragment is included in a region (aa 200-240) critical for the ability of AtMYB44 to function as a transcriptional activator. We hypothesize that the C-terminal side of the protein, but not the N-terminal side of the R2R3 domain, contributes to the functional activity and specificity of AtMYB44 through interactions with other regulators generated by each of a variety of stimuli.
