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Splicing of plant organellar group II introns from precursor-RNA transcripts requires the assistance of nuclear-encoded splicing factors. Maturase (nMAT) is one such factor, as its three homologs (nMAT1, 2 and 4) have been identified as being required for the splicing of various mitochondrial introns in Arabidopsis. However, the function of nMAT in maize (Zea mays L.) is unknown. In this study, we identified a seed development mutant, empty pericarp 2441 (emp2441) from maize, which showed severely arrested embryogenesis and endosperm development. Positional cloning and transgenic complementation assays revealed that Emp2441 encodes a maturase-related protein, ZmnMAT3. ZmnMAT3 is highly expressed during seed development and its protein locates to the mitochondria. The loss of function of ZmnMAT3 resulted in the reduced splicing efficiency of various mitochondrial group II introns, particularly of the trans -splicing of nad1 introns 1, 3 and 4, which consequently abolished the transcript of nad1 and severely impaired the assembly and activity of mitochondrial complex I. Moreover, the Zmnmat3 mutant showed defective mitochondrial structure and exhibited expression and activity of alternative oxidases. These results indicate that ZmnMAT3 is essential for mitochondrial complex I assembly during kernel development in maize. [ABSTRACT FROM AUTHOR]

The popularity of genomic selection (GS) has increased owing to its prospects in commercial breeding. It is necessary to enhance GS to increase its efficiency. In this study, a maize BC1F3:4 population, consisting of 481 families, was evaluated for days to anthesis in four environments, and genotyped with DNA chips including 55,000 single nucleotide polymorphisms (SNPs). This population was used to investigate whether GS could be enhanced by borrowing information from the genetic basis and genotype-by-environment (G × E) interaction. The results showed that: 1) fitting the top four large-effect SNPs as fixed effects could increase prediction accuracy, including three minor-effect SNPs explaining less than 10% phenotypic variance; 2) the increase of prediction accuracy when fitting large-effect SNPs as fixed effects was related to the decrease of genetic variance; 3) generally, the GS model fitting large-effect SNPs as fixed effects and G × E component enhanced GS. Therefore, we propose fitting large-effect markers as fixed effects and G × E effect for crop breeding projects in order to obtain accurately predicted phenotypic data and conduct efficient selection of desired plants. [ABSTRACT FROM AUTHOR]

Quantitative trait locus (QTL) mapping for seed longevity is essential for breeding modern cultivars with resistance to deterioration during postharvest storage. The inbred lines X178 and I178 showed large differences in seed vigour after artificial aging treatment, while they had similar performances in terms of most agronomic traits. An F2:3 population and a recombinant inbred line (RIL) population were generated to map QTL after 5 days under artificial aging conditions. Positive correlations were observed among all investigated traits including the aging germination rate, relative aging germination rate, aging simple vigour index, aging primary root length, aging shoot length and aging total length. Thirteen QTL were identified to locate on five chromosome regions: Chr.1:297 Mb (chromosome 1 region 297 Mb), Chr.3:205 Mb, Chr.4:240 Mb, Chr.5:205 Mb and Chr.7:155 Mb, with 2 to 4 QTL co‐located on a region. In each region, 3–8 previously identified aging‐related QTL were located, confirming the importance of these regions for controlling seed longevity in different maize populations. Taken together, the results of this work provide a foundation for further QTL fine mapping and the molecular‐assisted breeding of aging tolerant maize. [ABSTRACT FROM AUTHOR]

High-affinity ammonium uptake in maize roots is mainly mediated by AMT1-type ammonium transporters ZmAMT1;1a and ZmAMT1;3, but whether the increased expression of ZmAMTs genes is able to enhance ammonium uptake capacity and subsequently improves overall nitrogen use efficiency remains to be elucidated. In this work, ZmAMT1;1a-overexpression transgenic maize plants were generated with the elevated levels of transcripts and proteins, and phenotypically analyzed together with wild-type plants grown in nutrient solution under two regimes of ammonium supply. Under low ammonium nutrition (0.04 mM), in relative to wild-type plants, the maize transgenic lines showed an approximately 17% increases in the high-affinity ammonium uptake capacity of roots as revealed by 15N-labeled ammonium influx assay and further contributed to about 7% increases in the total nitrogen uptake at the whole plant level. By contrast, when ammonium was supplied in high amounts (1 mM), wild-type plants expressed higher levels of ZmAMT1;1a, but exhibited a lower ammonium uptake capacity in roots. Furthermore, the transgenic maize line accumulated more amounts of ZmAMT1;1a protein, but did not translate into an enhanced ammonium acquisition, suggesting a possible post-translational down-regulation of ZmAMT1;1a by high ammonium. This study proved the possibility to enhance ammonium acquisition by elevating ZmAMTs expression in maize roots and provided an effective transgenic approach on developing high nitrogen use efficient maize cultivars. [ABSTRACT FROM AUTHOR]

Maize ( Zea mays L.) root morphology exhibits a high degree of phenotypic plasticity to nitrogen (N) deficiency, but the underlying genetic architecture remains to be investigated. Using an advanced BC4F3 population, we investigated the root growth plasticity under two contrasted N levels and identified the quantitative trait loci (QTLs) with QTL-environment (Q × E) interaction effects. Principal components analysis (PCA) on changes of root traits to N deficiency (ΔLN-HN) showed that root length and biomass contributed for 45.8% in the same magnitude and direction on the first PC, while root traits scattered highly on PC2 and PC3. Hierarchical cluster analysis on traits for ΔLN-HN further assigned the BC4F3 lines into six groups, in which the special phenotypic responses to N deficiency was presented. These results revealed the complicated root plasticity of maize in response to N deficiency that can be caused by genotype-environment (G × E) interactions. Furthermore, QTL mapping using a multi-environment analysis identified 35 QTLs for root traits. Nine of these QTLs exhibited significant Q × E interaction effects. Taken together, our findings contribute to understanding the phenotypic and genotypic pattern of root plasticity to N deficiency, which will be useful for developing maize tolerance cultivars to N deficiency. [ABSTRACT FROM AUTHOR]