Ren-He Zhang

Photosynthetic performance of maize hybrids to drought stress

Maintaining photosynthetic activities is a critical function that allows crops to adapt to drought stress. We evaluated drought-induced changes in photosynthetic performance via gas exchange as well as photosynthetic electron transport and carbon assimilation process in two maize (Zea mays L.) cvs. Shaandan 609 (SD609) and Zhengdan 958 (ZD958). Plants were subjected to different intensity of drought stress inside of rain shelter. In both cultivars, moderate and severe drought stress caused a decrease in photosynthetic rate and stomatal conductance, but an increase in the intercellular CO2 concentration. Moreover, chlorophyll a fluorescence transients showed that drought stress significantly increased the positive Land K-band, revealing decreased function of oxygen-evolving complex, and decreased the fluorescence parameters reflecting electron flow from the intersystem carriers to the final reduction of PSI end electron acceptors. Also, moderate and severe drought stresses reduced both total activity and Rubisco activity. These parameters were more affected in ZD958 by drought stress compared to SD609. Based on our results, damaged PSII, reduced electron transport, and inactivation of Rubisco were main non-stomatal limitation of photosynthesis inhibition in both cultivars under moderate and severe drought stress. Photosynthetic apparatus of SD609 was more resistant to drought stress than that of ZD958.

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.

Effects of Different Cultivation Patterns on Photosynthetic Characteristics and Water Use Efficiency in Dryland Spring Maize

Under water-limited conditions,increasing water use efficiency(WUE) is essential for successful maize production.This study aimed at increasing grain yield and WUE through improving crop management.A maize cultivar Zhengdan 958 was planted at Changwu of Shaanxi Province in 2010 and 2011 with four treatments including local farmers practice(CK),high-yielding and high efficiency cultivation(HHC),super high yielding cultivation(SHC),and super high yielding and high efficiency cultivation(SHEC).The photosynthetic characteristics and WUE under the different cultivation patterns were analyzed.The results showed that the average yield for CK,HHC,SHC,and SHEC was 7.7,9.2,11.7,and 10.6 t ha~(-1),respectively,and 20.1%,52.9%,and 37.7% higher than that of control.WUE was increased by 27.8%,60.9%,and 45.1% under HHC,SHC,and SHEC,when compared with local farmers practice.Compared with the control,HHC,SHC and SHEC also significantly increased net photosynthetic rate(P_n),transpiration rate(T_r),leaf water use efficiency(WUE_L),electron transport rate(ETR),quantum yield(Φ_(PSII)),photochemical quenching(q_P) of photo-system II in leaf,delayed the mean decreasing rate of leaf senescence and leaf senescence duration.In addition,the post-anthesis dry matter accumulations were 29.0%,82.3%,and 56.1% higher in HHC,SHC,and SHEC than in the control.The results indicated that grain yield and WUE could be increased through integrating and optimizing cultivation techniques in maize production,which attributed to the higher photosynthetic rate,delayed leaf senescence at latter growth stages and higher post-anthesis dry matter accumulation and transportation to grains.

Effects of Abiotic Stress on Yield Traits of Maize Hybrids and Their Parental Inbred Lines

The field experiments were conducted to study the changes of grain yield and concerned physiological traits in stress-tolerant maize variety Zhengdan 958 and its parental inbred lines(Zheng 58 and Chang 7-2),as well as stress-sensitive maize variety Shaandan 902 and its parental inbred lines(K22 and K12) under different treatments of density(45 000 and 75 000 plants ha?1),nitrogen application(112.5 and 337.5 kg ha?1),and irrigation(normal irrigation and controlling water at prophase).The results showed that there were little differences in yield,mean leaf area index after anthesis,mean SPAD after anthesis,post-anthesis dry matter accumulation and harvest index between Zhengdan 958 and Shaandan 902 under resource-replete condi-tions(low density,high nitrogen and normal irrigation).But there were great differences in all traits(besides harvest index) be-tween Zhengdan 958 and Shaandan 902 under abiotic stress(high density,low nitrogen and drought stress),with much higher values in Zhengdan 958 than in Shaandan 902.Compared with Shaandan 902,mid-parent values of leaf area index,SPAD,post-anthesis dry matter accumulation and grain yield of Zhengdan 958 under abiotic stress(high density,low nitrogen and drought stress) increased by 45%,36%,51%,and 45%,respectively,and heterosis of Zhengdan 958 increased by 18%,9%,28%,and 22%,respectively.The mid-parent value of yield was much higher than heterosis of yield and both of them were higher in Zhengdan 958 than in Shaandan 902.So the maize variety Zhengdan 958 showed greater tolerance to abiotic stress which was mainly inherited from its parental inbred lines.Higher SPAD and LAI after anthesis contributed to post-anthesis dry matter accu-mulation,resulting in higher yield and higher stress tolerance.

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.