CFD-Guided Evaluation of Spark-Assisted Gasoline Compression Ignition for Cold Idle Operation

A closed-cycle, three-dimensional (3D) computational fluid dynamics (CFD) analysis campaign was conducted to evaluate the performance of using spark plugs to assist gasoline compression ignition (GCI) combustion during cold idle operations. A conventional spark plug using single-sided J-strap design was put at a location on the cylinder head to facilitate spray-guided spark assistance. Ignition was modeled with an L-type energy distribution to depict the breakdown and the arc-to-glow phases during the energy discharge process. Several key design parameters were investigated, including injector clocking, number of nozzle holes, spray inclusion angle, number of fuel injections, fuel split ratio, and fuel injection timings. The study emphasized the region around the spark gap, focusing on flame kernel formation and development and local equivalence ratio distribution. Flame kernel development and the ignition process were found to correlate strongly with the fuel stratification and the flow velocity near the spark gap. The analysis results showed that the flame kernel development followed the direction of the local flow field. In addition, the local fuel stratification notably influenced early-stage flame kernel development due to varying injection spray patterns and the fuel injection strategies. Among these design parameters, the number of nozzle holes and fuel injection timing had the most significant effects on the engine combustion performance.

Trihelix Transcription Factor ZmThx20 Is Required for Kernel Development in Maize

Maize kernels are the harvested portion of the plant and are related to the yield and quality of maize. The endosperm of maize is a large storage organ that constitutes 80–90% of the dry weight of mature kernels. Maize kernels have long been the study of cereal grain development to increase yield. In this study, a natural mutation that causes abnormal kernel development, and displays a shrunken kernel phenotype, was identified and named “shrunken 2008 (sh2008)”. The starch grains in sh2008 are loose and have a less proteinaceous matrix surrounding them. The total storage protein and the major storage protein zeins are ~70% of that in the wild-type control (WT); in particular, the 19 kDa and 22 kDa α-zeins. Map-based cloning revealed that sh2008 encodes a GT-2 trihelix transcription factor, ZmThx20. Using CRISPR/Cas9, two other alleles with mutated ZmThx20 were found to have the same abnormal kernel. Shrunken kernels can be rescued by overexpressing normal ZmThx20. Comparative transcriptome analysis of the kernels from sh2008 and WT showed that the GO terms of translation, ribosome, and nutrient reservoir activity were enriched in the down-regulated genes (sh2008/WT). In short, these changes can lead to defects in endosperm development and storage reserve filling in seeds.

Proteomics reveals the effects of drought stress on the kernel development and starch formation of waxy maize

Background Kernel development and starch formation are the primary determinants of maize yield and quality, which are considerably influenced by drought stress. To clarify the response of maize kernel to drought stress, we established well-watered (WW) and water-stressed (WS) conditions at 1–30 days after pollination (dap) on waxy maize (Zea mays L. sinensis Kulesh). Results Kernel development, starch accumulation, and activities of starch biosynthetic enzymes were significantly reduced by drought stress. The morphology of starch granules changed, whereas the grain filling rate was accelerated. A comparative proteomics approach was applied to analyze the proteome change in kernels under two treatments at 10 dap and 25 dap. Under the WS conditions, 487 and 465 differentially accumulated proteins (DAPs) were identified at 10 dap and 25 dap, respectively. Drought induced the downregulation of proteins involved in the oxidation–reduction process and oxidoreductase, peroxidase, catalase, glutamine synthetase, abscisic acid stress ripening 1, and lipoxygenase, which might be an important reason for the effect of drought stress on kernel development. Notably, several proteins involved in waxy maize endosperm and starch biosynthesis were upregulated at early-kernel stage under WS conditions, which might have accelerated endosperm development and starch synthesis. Additionally, 17 and 11 common DAPs were sustained in the upregulated and downregulated DAP groups, respectively, at 10 dap and 25 dap. Among these 28 proteins, four maize homologs (i.e., A0A1D6H543, B4FTP0, B6SLJ0, and A0A1D6H5J5) were considered as candidate proteins that affected kernel development and drought stress response by comparing with the rice genome. Conclusions The proteomic changes caused by drought were highly correlated with kernel development and starch accumulation, which were closely related to the final yield and quality of waxy maize. Our results provided a foundation for the enhanced understanding of kernel development and starch formation in response to drought stress in waxy maize.

PPR-DYW Protein EMP17 Is Required for Mitochondrial RNA Editing, Complex III Biogenesis, and Seed Development in Maize

The conversion of cytidines to uridines (C-to-U) at specific sites in mitochondrial and plastid transcripts is a post-transcriptional processing event that is important to the expression of organellar genes. Pentatricopeptide repeat (PPR) proteins are involved in this process. In this study, we report the function of a previously uncharacterized PPR-DYW protein, Empty pericarp17 (EMP17), in the C-to-U editing and kernel development in maize. EMP17 is targeted to mitochondria. The loss-function of EMP17 arrests maize kernel development, abolishes the editing at ccmFC-799 and nad2-677 sites, and reduces the editing at ccmFC-906 and -966 sites. The absence of editing causes amino acid residue changes in CcmFC-267 (Ser to Pro) and Nad2-226 (Phe to Ser), respectively. As CcmFC functions in cytochrome c (Cytc) maturation, the amount of Cytc and Cytc1 protein is drastically reduced in emp17, suggesting that the CcmFC-267 (Ser to Pro) change impairs the CcmFC function. As a result, the assembly of complex III is strikingly decreased in emp17. In contrast, the assembly of complex I appears less affected, suggesting that the Nad2-226 (Phe to Ser) change may have less impact on Nad2 function. Together, these results indicate that EMP17 is required for the C-to-U editing at several sites in mitochondrial transcripts, complex III biogenesis, and seed development in maize.

Genome-wide Identification and Expression Analysis of NAC Transcription Factor Family Genes during Fruit and Kernel Development in Siberian Apricot

The NAC (NAM, ATAF1/2, and CUC2) family is a group of plant-specific transcription factors that have vital roles in the growth and development of plants, and especially in fruit and kernel development. This study aimed to identify members of the NAC gene (PsNACs) family and investigate their functions in siberian apricot (Prunus sibirica). A total of 102 predicted PsNAC proteins (PsNACs) were divided into 14 clades and the genes were mapped to the eight chromosomes in siberian apricot. The PsNACs of the same clade had similar structures. A synteny analysis showed that the PsNACs had close relationships with the NAC genes of japanese apricot (Prunus mume). An expression pattern analysis of the PsNACs revealed many differences in various tissues and at different stages of fruit and kernel development. All eight PsNACs in clade XI have crucial roles in fruit and kernel development. Seven PsNACs (PsNACs 18, 64, 23, 33, 9, 4, and 50) in clades I, III, VI, VII, and XIII are related to fruit development. Eight PsNACs (PsNACs 6, 13, 46, 51, 41, 67, 37, and 59) in clades I, II, V, VIII, and XIII are involved in fruit ripening. Five PsNACs (PsNACs 6, 94, 41, 32, and 17) in clades I, IV, V, VII, and XI regulated the rapid growth of the kernel. Four PsNACs (PsNACs 50, 4, 67, and 84) in clades I, III, V, and XIII affected the hardening of the kernel. Four PsNACs (PsNACs 17, 82, 13, and 51) in clades II, XI, and IX acted on kernel maturation. We have characterized the NAC genes in siberian apricot during this study. Our results will provide resources for future research of the biological roles of PsNACs in fruit and kernel development in siberian apricot.