Summary Recent studies have revealed that microRNAs (miRNAs) regulate plant adaptive responses to nutrient deprivation. However, the functional significance of miRNAs in adaptive responses to nitrogen (N) limitation remains to be explored. The Arabidopsis miR169 was strongly down-regulated, whereas its targets, NFYA (Nuclear Factor Y, subunit A) family members, were strongly induced by nitrogen N starvation. Analysis of the expression of miR169 precursors showed that MIR169a was substantially down-regulated in both roots and shoots by N starvation. Accumulation of the NFYA family members was suppressed in transgenic Arabidopsis with constitutive expression of MIR169a. Transgenic Arabidopsis plants overexpressing MIR169a accumulated less N and were more sensitive to N stress than the wild type. N sensitivity of 35S::MIR169a might be attributable to impaired uptake systems. These results provide evidence that miRNAs have functional roles in helping plants to cope with fluctuations in N availability in the soil.

SummaryAlthough proteins in the basic helix-loop-helix (bHLH) family are universal transcription factors in eukaryotes, the biological roles of most bHLH family members are not well understood in plants.The Arabidopsis thaliana bHLH122 transcripts were strongly induced by drought, NaCl and osmotic stresses, but not by ABA treatment. Promoter::GUS analysis showed that bHLH122 was highly expressed in vascular tissues and guard cells. Compared with wild-type (WT) plants, transgenic plants overexpressing bHLH122 displayed greater resistance to drought, NaCl and osmotic stresses. In contrast, the bhlh122 loss-of-function mutant was more sensitive to NaCl and osmotic stresses than were WT plants.Microarray analysis indicated that bHLH122 was important for the expression of a number of abiotic stress-responsive genes. In electrophoretic mobility shift assay and chromatin immunoprecipitation assays, bHLH122 could bind directly to the G-box/E-box cis-elements in the CYP707A3 promoter, and repress its expression. Further, up-regulation of bHLH122 substantially increased cellular ABA levels.These results suggest that bHLH122 functions as a positive regulator of drought, NaCl and osmotic signaling.

Summary Histone methyltransferases (HMTases), as chromatin modifiers, regulate the transcriptomic landscape in normal development as well in diseases such as cancer. Here, we molecularly order two HMTases, EZH2 and MMSET that have established genetic links to oncogenesis. EZH2, which mediates histone H3K27 trimethylation and is associated with gene silencing, was shown to be coordinately expressed and function upstream of MMSET, which mediates H3K36 dimethylation and is associated with active transcription. We found that the EZH2-MMSET HMTase axis is coordinated by a microRNA network and that the oncogenic functions of EZH2 require MMSET activity. Together, these results suggest that the EZH2-MMSET HMTase axis coordinately functions as a master regulator of transcriptional repression, activation, and oncogenesis and may represent an attractive therapeutic target in cancer.