Dongwei Guo

Transcriptome Dynamics during Maize Endosperm Development.

The endosperm is a major organ of the seed that plays vital roles in determining seed weight and quality. However, genome-wide transcriptome patterns throughout maize endosperm development have not been comprehensively investigated to date. Accordingly, we performed a high-throughput RNA sequencing (RNA-seq) analysis of the maize endosperm transcriptome at 5, 10, 15 and 20 days after pollination (DAP). We found that more than 11,000 protein-coding genes underwent alternative splicing (AS) events during the four developmental stages studied. These genes were mainly involved in intracellular protein transport, signal transmission, cellular carbohydrate metabolism, cellular lipid metabolism, lipid biosynthesis, protein modification, histone modification, cellular amino acid metabolism, and DNA repair. Additionally, 7,633 genes, including 473 transcription factors (TFs), were differentially expressed among the four developmental stages. The differentially expressed TFs were from 50 families, including the bZIP, WRKY, GeBP and ARF families. Further analysis of the stage-specific TFs showed that binding, nucleus and ligand-dependent nuclear receptor activities might be important at 5 DAP, that immune responses, signalling, binding and lumen development are involved at 10 DAP, that protein metabolic processes and the cytoplasm might be important at 15 DAP, and that the responses to various stimuli are different at 20 DAP compared with the other developmental stages. This RNA-seq analysis provides novel, comprehensive insights into the transcriptome dynamics during early endosperm development in maize.

Identification of favorable alleles in the non-yellow coloring 1 gene by association mapping in maize

Association mapping was conducted to explore favorable alleles of the chlorophyll-related non-yellow coloring 1 (NYC1) gene under light and dark using an association panel of 146 maize inbred lines. A total of 14 polymorphic sites were identified to be significantly associated with at least one of the chlorophyll-related traits at the seedling stage. Four single nucleotide polymorphisms (SNPs) (S320, S2951, S3901, and S3355) from the NYC1 gene were respectively strongly associated with chlorophyll b (chlb), the ratio of chlorophyll a to chlorophyll b (chl_ratio), chlorophyll a degradation (chla_deg), and total chlorophyll degradation (total_chl_deg). SNPs S320 (C/A) in exon 1, and S2951 (A/G) in intron 8 was related to chlb, with 6.01 and 8.89% of phenotypic variation under light treatment, respectively. Under dark treatment, SNP S3901 (C/T), located in 3′ untranslated region (3′UTR), was associated with chl_ratio, explaining 7.01% of the observed phenotypic variation, whereas SNP S3355 (C/G) in intron 9 explained 6.48 and 5.18% of phenotypic variations in chla_deg and total_chl_deg, respectively. Taken together, these results indicated that the NYC1 gene plays an important role in chlorophyll content and other related traits, and different sites act on chlorophyll metabolism under different light intensities in maize seedlings. Furthermore, these findings improve our understanding of the genetic basis of chlorophyll metabolism under different light conditions.

Evolutionary, structural and expression analysis of core genes involved in starch synthesis

Starch is the main storage carbohydrate in plants and an important natural resource for food, feed and industrial raw materials. However, the details regarding the pathway for starch biosynthesis and the diversity of biosynthetic enzymes involved in this process are poorly understood. This study uses a comprehensive phylogenetic analysis of 74 sequenced plant genomes to revisit the evolutionary history of the genes encoding ADP-glucose pyrophosphorylase (AGPase), starch synthase (SS), starch branching enzyme (SBE) and starch de-branching enzyme (DBE). Additionally, the protein structures and expression patterns of these four core genes in starch biosynthesis were studied to determine their functional differences. The results showed that AGPase, SS, SBE and DBE have undergone complicated evolutionary processes in plants and that gene/genome duplications are responsible for the observed differences in isoform numbers. A structure analysis of these proteins suggested that the deletion/mutation of amino acids in some active sites resulted in not only structural variation but also sub-functionalization or neo-functionalization. Expression profiling indicated that AGPase-, SS-, SBE- and DBE-encoding genes exhibit spatio-temporally divergent expression patterns related to the composition of functional complexes in starch biosynthesis. This study provides a comprehensive atlas of the starch biosynthetic pathway, and these data should support future studies aimed at increasing understanding of starch biosynthesis and the functional evolutionary divergence of AGPase, SS, SBE, and DBE in plants.

ZmSMR4, a novel cyclin-dependent kinase inhibitor (CKI) gene in maize (Zea mays L.), functions as a key player in plant growth, development and tolerance to abiotic stress

Endoreduplication is a key cell cycle variant in the developing maize endosperm and has been associated with cell enlargement and dry matter accumulation. Therefore, identification of the key genes associated with endosperm development and endoreduplication would not only lay the groundwork for understanding the biological process of endoreduplication but also be important for maize breeding. Here, we identified 12 putative endoreduplication-related candidate genes as members of the Zea mays L. SIAMESE-RELATED (ZmSMR) gene family and denoted them ZmSMR1-ZmSMR12. Sequence analysis indicated that all the ZmSMR protein sequences exhibited modest sequence similarity to the SIAMESE gene from Arabidopsis. Further analyses suggested that most ZmSMR genes might be associated with the transition from mitosis to endoreduplication because the expression levels of most ZmSMR genes were upregulated in endosperm cells during the phase of switching to an endoreduplication cell cycle. Additionally, the ZmSMRs responded to various abiotic stresses at the transcriptional level. One member of the ZmSMR gene family, the ZmSMR4 (KY946768) gene, was isolated as the first maize endoreduplication-related gene and has been used to develop transgenic Arabidopsis plants. ZmSMR4 was localized to the nucleus and could interact with ZmCDKA and ZmCDKB. Moreover, ZmSMR4 was able to rescue the multicellular trichome phenotype of Arabidopsis sim mutants and enhanced the endoreduplication levels of transgenic Arabidopsis plants. Arabidopsis plants overexpressing ZmSMR4 not only displayed enhanced leaf margin serrations but also showed several interesting breeding phenotypes, such as early blossoming and fuller seeds. Taken together, our data suggest that the ZmSMR4 gene is plant-specific and functions as a key player in the signalling network that controls plant growth, development and responses to abiotic stress by regulating the transition between the mitotic cycle and endoreduplication.

Effects of Different Thermal Treatment Methods on Preparation and Physical Properties of High Amylose Maize Starch Based Films

Abstract Because of its biodegradable trait, starch has been widely used as the raw material for packaging. Effects of different thermal treatment methods (high temperature-high pressure heating (HH), microwave heating (MH) and alkali heating (AH) with and without glycerol on physical properties of high amylose maize starch films (HASFs) were investigated in this study. HASFs under HH had highest elongation at break (E%), and lowest tensile strength (TS), modulus of elasticity (EM) and opacity (OC). HASFs under MH had highest TS, water holding capacity (WHC) and OC, and lowest thickness (TN), E%, solubility in water (SW) and solubility in oil (SO), while HASFs under AH had highest TN, EM, SW and SO, and lowest WHC. Compared with water, plasticized HASFs with glycerol had higher TN，E%, WHC, SW and OC, and lower TS, EM and SO. XRD results revealed the V-type polymorph and the difference in intensity of diffraction peaks of HASFs under three methods. This study would be helpful to design and prepare HASFs.

Bivariate flow cytometric analysis and sorting of different types of maize starch grains

Particle‐size distribution, granular structure, and composition significantly affect the physicochemical properties, rheological properties, and nutritional function of starch. Flow cytometry and flow sorting are widely considered convenient and efficient ways of classifying and separating natural biological particles or other substances into subpopulations, respectively, based on the differential response of each component to stimulation by a light beam; the results allow for the correlation analysis of parameters. In this study, different types of starches isolated from waxy maize, sweet maize, high‐amylose maize, pop maize, and normal maize were initially classified into various subgroups by flow cytometer and then collected through flow sorting to observe their morphology and particle‐size distribution. The results showed that a 0.25% Gelzan solution served as an optimal reagent for keeping individual starch particles homogeneously dispersed in suspension for a relatively long time. The bivariate flow cytometric population distributions indicated that the starches of normal maize, sweet maize, and pop maize were divided into two subgroups, whereas high‐amylose maize starch had only one subgroup. Waxy maize starch, conversely, showed three subpopulations. The subgroups sorted by flow cytometer were determined and verified in terms of morphology and granule size by scanning electron microscopy and laser particle distribution analyzer. Results showed that flow cytometry can be regarded as a novel method for classifying and sorting starch granules.

Genetic characterization of inbred lines from Shaan A and B groups for identifying loci associated with maize grain yield

BackgroundIncreasing grain yield is a primary objective of maize breeding. Dissecting the genetic architecture of grain yield furthers genetic improvements to increase yield. Presented here is an association panel composed of 126 maize inbreds (AM126), which were genotyped by the genotyping-by-sequencing (tGBS) method. We performed genetic characterization and association analysis related to grain yield in the association panel.ResultsIn total, 46,046 SNPs with a minor allele frequency (MAF) ≥0.01 were used to assess genetic diversity and kinship in AM126. The results showed that the average MAF and polymorphism information content (PIC) were 0.164 and 0.198, respectively. The Shaan B group, with 11,284 unique SNPs, exhibited greater genetic diversity than did the Shaan A group, with 2644 SNPs. The 61.82% kinship coefficient in AM126 was equal to 0, and only 0.15% of that percentage was greater than 0.7. A total of 31,983 SNPs with MAF ≥0.05 were used to characterize population structure, LD decay and association mapping. Population structure analysis suggested that AM126 can be divided into 6 subgroups, which is consistent with breeding experience and pedigree information. The LD decay distance in AM126 was 150xa0kb. A total of 51 significant SNPs associated with grain yield were identified at Pu2009<u20091u2009×u200910−u20093 across two environments (Yangling and Yulin). Among those SNPs, two loci displayed overlapping regions in the two environments. Finally, 30 candidate genes were found to be associated with grain yield.ConclusionsThese results contribute to the genetic characterization of this breeding population, which serves as a reference for hybrid breeding and population improvement, and demonstrate the genetic architecture of maize grain yield, potentially facilitating genetic improvement.