Fructokinases (FRKs) are key regulators in carbohydrate metabolism and plant development. However, their specific functions in crop photosynthesis and sugar metabolism remain unclear. In this study, we identified three rice FRKs (OsFRK1, OsFRK2, and OsFRK3), investigating their catalytic activities, expression pattern, and subcellular localization. OsFRK1 and OsFRK2 localized to the cytosol, whereas OsFRK3 localized to chloroplasts, indicating spatially distinct functions. Using CRISPR/Cas9, we generated single mutants (osfrk1, osfrk2, osfrk3) and a double mutant osfrk1×osfrk2 deficient in both cytosolic OsFRKs. All mutants showed significantly reduced plant height, biomass, and grain yield under field conditions. At the physiological level, OsFRK mutants displayed markedly reduced OsFRK enzyme activity, accompanied by impaired photosynthetic efficiency, excessive starch and fructose accumulation in leaves, and elevated sucrose and fructose levels in grains. Loss function of OsFRKs also triggered metabolic compensation in source leaves, including elevated activities of sucrose-degradation enzymes and hexokinase. Additionally, haplotype analysis identified elite alleles of OsFRKs: FRK1^C (higher panicle number), FRK2^C (greater 1000-grain weight), and FRK3^A (higher panicle number). Cultivars carrying the combined haplotypes (FRK1^C–FRK2^C–FRK3^A) exhibited higher grain yields than other genotype combinations. Together, these findings revealed cytosolic and chloroplastic OsFRKs in regulating rice photosynthesis, sugar allocation, and yield formation, and highlighted the elite OsFRK haplotypes as valuable genetic resources for future rice improvement.

In rainfed areas of northwestern China, maize production is constrained mainly by low temperature during early growth and water limitation during the entire growth period. Plastic film mulching is commonly used to increase maize yield in this area, because it increases topsoil temperature and moisture content as well as water use efficiency. However, the physiological and anatomical bases of maize yield improvement with plastic film mulching are not well understood. The effects of plastic film mulching and planting density on maize yield, photosynthetic characteristics, respiration, leaf anatomy, and root growth were studied in a two-year field experiment conducted on the Loess Plateau of China in 2017 and 2018. The experiment used a split-split plot design with two mulching treatments (plastic film mulching and no mulching), two planting densities (7.5 × 10⁴ and 10.5 × 10⁴ plants ha⁻¹), and two maize cultivars, Zhengdan 958 and Xianyu 335. Compared with no mulching, plastic film mulching increased maize yields by 31.1%–46.4% in 2017 and 3.6%–34.7% in 2018. Compared with low planting density, high planting density significantly increased and slightly reduced yields of both cultivars in the dry year 2017 and the rainy year 2018, respectively. Plastic film mulching increased photosynthesis and respiration as well as leaf stomatal density and aperture. Photosynthetic rate, dark respiration, and stomatal conductance and aperture were lower at high planting than at low planting density. Maize yield was positively correlated with photosynthesis, dark respiration, and stomatal aperture. Mulching increased root dry weight and length in the 0–20 cm soil layer and root activity at maturity. Overall, the changes in root growth and leaf anatomy resulted in increased photosynthesis and dark respiration, and the increased photosynthesis contributed to the increase in grain yield and biomass production under plastic film mulching conditions. Our results increase understanding of the physiological mechanisms by which plastic film mulching increases maize yield in water- and temperature-limited areas.