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Summary: Seed vigour, including rapid, uniform germination and robust seedling establishment under various field conditions, is becoming an increasingly essential agronomic trait for achieving high yield in crops. However, little is known about this important seed quality trait. In this study, we performed a genome‐wide association study to identify a key transcription factor ZmRap2.7, which regulates seed vigour through transcriptionally repressing expressions of three ABA signalling genes ZmPYL3, ZmPP2C and ZmABI5 and two phosphatidylethanolamine‐binding genes ZCN9 and ZCN10. In addition, ZCN9 and ZCN10 proteins could interact with ZmPYL3, ZmPP2C and ZmABI5 proteins, and loss‐of‐function of ZmRap2.7 and overexpression of ZCN9 and ZCN10 reduced ABA sensitivity and seed vigour, suggesting a complex regulatory network for regulation of ABA signalling mediated seed vigour. Finally, we showed that four SNPs in ZmRap2.7 coding region influenced its transcriptionally binding activity to the downstream gene promoters. Together with previously identified functional variants within and surrounding ZmRap2.7, we concluded that the distinct allelic variations of ZmRap2.7 were obtained independently during maize domestication and improvement, and responded separately for the diversities of seed vigour, flowering time and brace root development. These results provide novel genes, a new regulatory network and an evolutional mechanism for understanding the molecular mechanism of seed vigour. [ABSTRACT FROM AUTHOR]

Summary: Nitrate (NO3−) is crucial for optimal plant growth and development and often limits crop productivity under low availability. In comparison with model plant Arabidopsis, the molecular mechanisms underlying NO3− acquisition and utilization remain largely unclear in maize. In particular, only a few genes have been exploited to improve nitrogen use efficiency (NUE). Here, we demonstrated that NO3−‐inducible ZmNRT1.1B (ZmNPF6.6) positively regulated NO3−‐dependent growth and NUE in maize. We showed that the tandem duplicated proteoform ZmNRT1.1C is irrelevant to maize seedling growth under NO3− supply; however, the loss of function of ZmNRT1.1B significantly weakened plant growth under adequate NO3− supply under both hydroponic and field conditions. The 15N‐labelled NO3− absorption assay indicated that ZmNRT1.1B mediated the high‐affinity NO3−‐transport and root‐to‐shoot NO3− translocation. Transcriptome analysis further showed, upon NO3− supply, ZmNRT1.1B promotes cytoplasmic‐to‐nuclear shuttling of ZmNLP3.1 (ZmNLP8), which co‐regulates the expression of genes involved in NO3− response, cytokinin biosynthesis and carbon metabolism. Remarkably, overexpression of ZmNRT1.1B in modern maize hybrids improved grain yield under N‐limiting fields. Taken together, our study revealed a crucial role of ZmNRT1.1B in high‐affinity NO3− transport and signalling and offers valuable genetic resource for breeding N use efficient high‐yield cultivars. [ABSTRACT FROM AUTHOR]

High planting density is essential to increasing maize grain yield. However, single plants suffer from insufficient light under high planting density. Ammonium (NH4+) assimilation consumes less energy converted from radiation than nitrate (NO3−). It is hypothesized that a mixed NO3−/NH4+ supply is more important to improving plant growth and population productivity under high vs. low planting density. Maize plants were grown under hydroponic conditions at two planting densities (low density: 208 plants m−2 and high density: 667 plants m−2) and three nitrogen forms (nitrate only, 75/25NO3−/NH4+ and ammonium only). A significant interaction effect was found between planting density and N form on plant biomass. Compared to nitrate only, 75/25NO3−/NH4+ increased per-plant biomass by 44% under low density, but by 81% under high density. Treatment with 75/25NO3−/NH4+ increased plant ATP, photosynthetic rate, and carbon amount per plant by 31, 7, and 44% under low density, respectively, but by 51, 23, and 95% under high density. Accordingly, carbon level per plant under 75/25NO3−/NH4+ was improved, which increased leaf area, specific leaf weight and total root length, especially for high planting density, increased by 57, 17 and 63%, respectively. Furthermore, under low density, 75/25NO3−/NH4+ increased nitrogen uptake rate, while under high density, 75/25NO3−/NH4+ increased nitrogen, phosphorus, copper and iron uptake rates. By increasing energy use efficiency, an optimum NO3−/NH4+ ratio can improve plant growth and nutrient uptake efficiency, especially under high planting density. In summary, an appropriate supply of NH4+ in addition to nitrate can greatly improve plant growth and promote population productivity of maize under high planting density, and therefore a mixed N form is recommended for high-yielding maize management in the field.