Grain size determines grain weight and affects grain quality. Several major quantitative trait loci (QTLs) regulating grain size have been cloned; however, our understanding of the underlying mechanism that regulates the size of rice grains remains fragmentary. Here, we report the cloning and characterization of a dominant QTL, grain size on chromosome 2 (GS2), which encodes Growth-Regulating Factor 4 (OsGRF4), a transcriptional regulator. GS2 localizes to the nucleus and may act as a transcription activator. A rare mutation of GS2 affecting the binding site of a microRNA, OsmiR396c, causes elevated expression of GS2/OsGRF4. The increase in GS2 expression leads to larger cells and increased numbers of cells, which thus enhances grain weight and yield. The introduction of this rare allele of GS2/OsGRF4 into rice cultivars could significantly enhance grain weight and increase grain yield, with possible applications in breeding high-yield rice varieties.
Summary ATP ‐citrate lyases ( ACL ) play critical roles in tumour cell propagation, foetal development and growth, and histone acetylation in human and animals. Here, we report a novel function of ACL in cell death‐mediated pathogen defence responses in rice. Using ethyl methanesulphonate ( EMS ) mutagenesis and map‐based cloning, we identified an Oryza sativa ACL ‐A2 mutant allele, termed spotted leaf 30‐1 ( spl30‐1 ), in which an A‐to‐T transversion converts an Asn at position 343 to a Tyr (N343Y), causing a recessive mutation that led to a lesion mimic phenotype. Compared to wild‐type plants, spl30‐1 significantly reduces ACL enzymatic activity, accumulates high reactive oxygen species and increases degradation rate of nuclear deoxyribonucleic acids. CRISPR /Cas9‐mediated insertion/deletion mutation analysis and complementation assay confirmed that the phenotype of spl30‐1 resulted from the defective function of Os ACL ‐A2 protein. We further biochemically identified that the N343Y mutation caused a significant degradation of SPL 30 N343Y in a ubiquitin‐26S proteasome system ( UPS )‐dependent manner without alteration in transcripts of Os ACL ‐A2 in spl30‐1 . Transcriptome analysis identified a number of up‐regulated genes associated with pathogen defence responses in recessive mutants of Os ACL ‐A2, implying its role in innate immunity. Suppressor mutant screen suggested that Os SL , which encodes a P450 monooxygenase protein, acted as a downstream key regulator in spl30‐1 ‐mediated pathogen defence responses. Taken together, our study discovered a novel role of Os ACL ‐A2 in negatively regulating innate immune responses in rice.
Chemical studies on the constituents of Dracaena cochinchinensis led to the discovery of eight new flavonoid derivatives (1–8) along with 14 known compounds (9–22). The identification and structural elucidation of these isolates were based on spectral analyses. All isolates were tested for antibacterial activities against Helicobacter pylori (ATCC43504) and thrombin inhibitory effects. As a result, new flavonoid derivatives 6 and 7 and (2S)-4′,7-dihydroxy-8-methylflavan (11) were found to be most efficacious against H. pylori (ATCC43504) with MIC values of 29.5, 29.5, and 31.3 µM, respectively, and the seven new flavonoid derivatives (1–7) and one known biflavonoid (9) were observed to exhibit moderate thrombin inhibitory activity.
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