Cereal crops are a primary energy source for humans. Grain size and weight affect both evolutionary fitness and grain yield of cereals. Although studies on gene mining and molecular mechanisms controlling grain size and weight are constantly emerging in cereal crops, only a few systematic reviews on the underlying molecular mechanisms and their breeding applications are available so far. This review provides a general state-of-the-art overview of molecular mechanisms and targeted strategies for improving grain size and weight of cereals as well as insights for future yield-improving biotechnology-assisted breeding. In this review, the evolution of research on grain size and weight over the last 20 years is traced based on a bibliometric analysis of 1158 publications and the main signaling pathways and transcriptional factors involved are summarized. In addition, the roles of post-transcriptional regulation and photosynthetic product accumulation affecting grain size and weight in maize and rice are outlined. State-of-the-art strategies for discovering novel genes related to grain size and weight in maize and other cereal crops as well as advanced breeding biotechnology strategies being used for improving yield including marker-assisted selection, genomic selection, transgenic breeding, and genome editing are also discussed.

Grain yield is the most critical and complex quantitative trait in maize. Kernel length (KL), kernel width (KW), kernel thickness (KT) and hundred-kernel weight (HKW) associated with kernel size are essential components of yield-related traits in maize. With the extensive use of quantitative trait locus (QTL) mapping and genome-wide association study (GWAS) analyses, thousands of QTLs and quantitative trait nucleotides (QTNs) have been discovered for controlling these traits. However, only some of them have been cloned and successfully utilized in breeding programs. In this study, we exhaustively collected reported genes, QTLs and QTNs associated with the four traits, performed cluster identification of QTLs and QTNs, then combined QTL and QTN clusters to detect consensus hotspot regions. In total, 31 hotspots were identified for kernel size-related traits. Their candidate genes were predicted to be related to well-known pathways regulating the kernel developmental process. The identified hotspots can be further explored for fine mapping and candidate gene validation. Finally, we provided a strategy for high yield and quality maize. This study will not only facilitate causal genes cloning, but also guide the breeding practice for maize.

Flax lignans are abundant plant secondary metabolites in flaxseed, with secoisolariciresinol diglucoside (SDG) content reaching 0.61–1.33% of seed dry weight—substantially higher than levels reported for sesame seeds (0.01–0.03%), cereals (<0.01%), and most legumes (<0.005%). These levels make them natural bioactive compounds with considerable application potential. This review summarizes the biosynthetic pathways, key enzymes, and regulatory mechanisms of flax lignans; describes their major biological activities, including antioxidant, anti-inflammatory, anticancer, cardiovascular protective, and metabolic regulatory effects and possible mechanisms of action; and analyzes current progress in extraction, purification, analytical detection, and application. Key limitations in industrial application include complex extraction procedures, high production costs, lack of unified quality standards, and insufficient clinical evidence. Advanced strategies such as synthetic biology approaches for heterologous production, molecular breeding for high-lignan varieties, and green extraction technologies are discussed as promising solutions. This review is intended to serve as a conceptual reference for subsequent mechanistic studies, product development, and industrial translation of flax lignans in food, pharmaceutical, and cosmetic applications.