Wheat is one of the most important food crops globally, and understanding the regulation of grain size is crucial for wheat breeding to achieve a higher grain yield. MicroRNAs (miRNAs) play vital roles in plant growth and development. However, the miRNA-mediated mechanism underlying grain size regulation remains largely elusive in wheat. Here, we report the characterization and functional validation of a miRNA, TamiR397a, associated with grain size regulation in wheat. The function of three TaMIR397 homoeologs was determined through histochemical β-glucuronidase-dependent assay. MiRNA expression was detected using quantitative reverse transcription polymerase chain reaction (qRT-PCR), and the function of TamiR397a was validated through its transgenic overexpression and repression in wheat. It was found that TaMIR397-6A and TaMIR397-6B encode active TamiR397a. The expression profiling indicated that TamiR397a was differentially expressed in various tissues and gradually up-regulated during grain filling. The inhibition of TamiR397a perturbed grain development, leading to a decrease in grain size and weight. Conversely, the overexpression of TamiR397a resulted in increased grain size and weight by accelerating the grain filling process. Transcriptome analysis revealed that TamiR397a regulates a set of genes involved in hormone response, desiccation tolerance, regulation of cellular senescence, seed dormancy, and seed maturation biological processes, which are important for grain development. Among the down-regulated genes in the grains of the TamiR397a-overexpressing transgenic plants, 11 putative targets of the miRNA were identified. Taken together, our results demonstrate that TamiR397a is a positive regulator of grain size and weight, offering potential targets for breeding wheat with an increased grain yield.

Background/Objectives: Kernel dehydration is an important agronomic trait influencing mechanical harvesting efficiency, post-harvest drying costs, and grain storage quality in maize (Zea mays L.). Although the genetic and molecular basis of whole-kernel dehydration has been increasingly investigated, tissue-specific physiological and molecular patterns, particularly those associated with the embryo, remain insufficiently characterized. In this study, four maize inbred lines with contrasting dehydration capacities were selected to characterize tissue-specific dehydration dynamics and associated molecular patterns. Methods: Moisture content and dehydration rates of kernels, endosperms, and embryos were monitored from 10 to 55 days after pollination (DAP), followed by correlation analyses with kernel- and ear-related agronomic traits. Transcriptome sequencing, weighted gene co-expression network analysis (WGCNA), and untargeted metabolomics were integrated to characterize molecular processes associated with contrasting embryo dehydration phenotypes. Results: Embryo dehydration closely paralleled whole-kernel dehydration, and embryo dehydration rate was strongly associated with kernel dehydration rate. Transcriptomic and WGCNA analyses revealed developmental- and genotype-dependent expression changes, particularly during late maturation, and identified dehydration-associated modules enriched in lipid metabolism, glycolysis, hormone signaling, and stress-responsive processes, including fatty acid metabolism, ABA- and ethylene-related signaling, and MAPK-related genes. FDR-controlled metabolomics further revealed genotype- and developmental-stage-dependent metabolite differences associated with organic acid metabolism, amino acid metabolism, transport-associated processes, and secondary metabolism. Pathway-level integration highlighted ABA- and ethylene-associated candidate processes associated with variation in embryo dehydration. Conclusions: Collectively, these findings provide an embryo-focused characterization of physiological and multi-omics variation associated with maize kernel dehydration and identify candidate molecular processes for further functional investigation. Further validation across broader germplasm panels, environmental conditions, and experimental systems will be required to determine the causal roles and potential breeding relevance of these candidate processes.