A Carbonic Anhydrase, ZmCA4, Contributes to Photosynthetic Efficiency and Modulates CO2 Signaling Gene Expression by Interacting with Aquaporin ZmPIP2;6 in Maize.

Carbonic anhydrase (CA) catalyzes the reversible CO2 hydration reaction that produces bicarbonate for phosphoenolpyruvate carboxylase (PEPC). This is the initial step for transmitting the CO2 signal in C4 photosynthesis. However, it remains unknown whether the maize (Zea mays L.) CA gene, ZmCA4, plays a role in the maize photosynthesis process. In our study, we found that ZmCA4 was relatively highly expressed in leaves and localized in the chloroplast and the plasma membrane of mesophyll protoplasts. Knock-out of ZmCA4 reduced CA activity, while overexpression of ZmCA4 increased rubisco activity, as well as the quantum yield and relative electron transport rate in photosystem II. Overexpression of ZmCA4 enhanced maize yield-related traits. Moreover, ZmCA4 interacted with aquaporin ZmPIP2;6 in bimolecular fluorescence complementation and co-immunoprecipitation experiments. The double-knock-out mutant for ZmPIP2;6 and ZmCA4 genes showed reductions in its growth, CA and PEPC activities, assimilation rate and photosystem activity. RNA-Seq analysis revealed that the expression of other ZmCAs, ZmPIPs, as well as CO2 signaling pathway homologous genes, and photosynthetic-related genes was all altered in the double-knock-out mutant compared with the wild type. Altogether, our study's findings point to a critical role of ZmCA4 in determining photosynthetic capacity and modulating CO2 signaling regulation via its interaction with ZmPIP2;6, thus providing insight into the potential genetic value of ZmCA4 for maize yield improvement.

A new network containing MYB109-ZmCesA5 is involved in kernel development.

MYB genes regulate several different aspects of metabolism and development. However, few studies have reported the involvement of MYBs-CesAs network in the regulation of maize kernel development. In this study, yeast one-hybrid (Y1H) assays and dual-luciferase reporter assays showed that ZmMYB109 activated the expression of ZmCesA5 by directly binding to its promoter. Real-time quantitative PCR (RT-qPCR) and transcriptome analyses showed that ZmMYB109 expression increased in ZmCesA5-OE kernels and decreased in ZmCesA5-KO kernels. Overexpression of ZmCesA5 produced heavier kernels, whereas loss of function of ZmCesA5 affected starch and sucrose metabolism, resulting in weight reduction of the maize kernels. Collectively, these findings suggest that a new network containing MYB109-ZmCesA5 is involved in kernel development.

Maize transcription factor ZmNF-YC13 regulates plant architecture.

Leaf angle and leaf orientation value (LOV) are critical agronomic traits for maize plant architecture. The functions of NUCLEAR FACTOR Y (NF-Y) members in regulating plant architecture have not been reported yet. Here, we identified a regulator of maize plant architecture, NF-Y subunit C13 (ZmNF-YC13). ZmNF-YC13 was highly expressed in the leaf base zone of maize plants. ZmNF-YC13 overexpressing plants showed upright leaves with narrow leaf angle and larger LOV, while ZmNF-YC13 knockout plants had larger leaf angle and smaller LOV compared with wild-type plants. The changes in plant architecture were due to the changes in the expression of cytochrome P450 family members. ZmNF-YC13 interacts with two NF-Y subunit B members (ZmNF-YB9 and ZmNF-YB10) of the LEAFY COTYLEDON1 sub-family, and further recruits NF-Y subunit A (ZmNF-YA3) to form two NF-Y complexes. The two complexes can both activate the promoters of transcriptional repressors (ZmWRKY76 and ZmBT2), and the promoters of PLASTOCHRON group genes can be repressed by ZmWRKY76 and ZmBT2 in maize protoplasts. We propose that ZmNF-YC13 functions as a transcriptional regulator and, together with ZmNF-YBs and ZmNF-YA3, affects plant architecture by regulating the expression of ZmWRKY76 and ZmBT2, which repress the expression of cytochrome P450 family members in PLASTOCHRON branch.

Identification of Building Damage from UAV-Based Photogrammetric Point Clouds Using Supervoxel Segmentation and Latent Dirichlet Allocation Model.

Accurate assessment of building damage is very important for disaster response and rescue. Traditional damage detection techniques using 2D features at a single observing angle cannot objectively and accurately reflect the structural damage conditions. With the development of unmanned aerial vehicle photogrammetric techniques and 3D point processing, automatic and accurate damage detection for building roof and facade has become a research hotspot in recent work. In this paper, we propose a building damage detection framework based on the boundary refined supervoxel segmentation and random forest-latent Dirichlet allocation classification. First, the traditional supervoxel segmentation method is improved to segment the point clouds into good boundary refined supervoxels. Then, non-building points such as ground and vegetation are removed from the generated supervoxels. Next, latent Dirichlet allocation (LDA) model is used to construct the high-level feature representation for each building supervoxel based on the selected 2D image and 3D point features. Finally, LDA model and random forest algorithm are employed to identify the damaged building regions. This method is applied to oblique photogrammetric point clouds collected from the Beichuan Country Earthquake Site. The research achieves the 3D damage assessment for building facade and roof. The result demonstrates that the proposed framework is capable of achieving around 94% accuracy for building point extraction and around 90% accuracy for damage identification. Moreover, both of the precision and recall for building damage detection reached around 89%. Concluded from comparison analysis, the proposed method improved the damage detection accuracy and the highest improvement ratio is over 8%.

Identification and epistasis analysis of quantitative trait loci for zeaxanthin concentration in maize kernel across different generations and environments.

Zeaxanthin, a natural fat-soluble pigment, not only increases plant resistance, but also has vital significance for human health. However, quantitative trait loci (QTL) and the epistatic effects of zeaxanthin concentration in maize kernel have not been well studied. To identify QTLs and analyse the epistatic effects of zeaxanthin concentration in maize kernel, two sets of segregating generations derived from the cross between HuangC (a high zeaxanthin concentration inbred line) and Rezi1 (a low zeaxanthin concentration inbred line) were evaluated in three different environments. One major-effect QTL, qZea6a, explains 41.4-71.4% of the phenotypic variation and two QTLs, qZea4a and qZea3a, show LOD > 3 for zeaxanthin concentration detected over two generations and three different environments. Four of the ten QTL pairs show epistatic effects, explaining 7.34-14.3% of the phenotypic variance. Furthermore, additivity was the major allelic action at zeaxanthin concentration QTLs located in F2 and F2:3 populations and plants with homozygous HuangC alleles have a strong genetic ability in enhancing zeaxanthin concentration in maize kernel. These results will contribute to understanding these complex loci better and provide awareness about zeaxanthin concentration to maize breeders and scientists involved in maize research.

Comparative investigation on thermal decomposition of powdered and pelletized biomasses: Thermal conversion characteristics and apparent kinetics.

In this work, the thermal degradation behaviors of two kinds of biomasses (pinewood and rice husk) with powder and pellet under three oxygen concentrations were investigated by a self-designed macro-thermogravimetric analyzer. An obvious hysteresis of thermal degradation of biomass pellets was observed under three conditions. The maximum activation energy of biomass pellets was significantly greater than that of biomass powders, while their average activation energies were almost equal based on distributed activation energy model. For the oxygen-rich combustion, the comprehensive combustion character index of powdered and pelletized biomasses ranged from 3.92 × 10-7 to 5.16 × 10-7%2·min-2·°C-3 and from 1.82 × 10-7 to 1.91 × 10-7%2·min-2·°C-3, respectively. Furthermore, the derived biochar of powdered biomass has a higher caloricity than that of pelletized biomass during combustion by TG-DSC analysis. The performances of thermal degradation observed by macro-thermogravimetric analyzer could factually reveal the influence of mass and heat transfer on the thermochemical conversion of powdered and pelletized biomasses.

Overexpression of the maize transcription factor ZmVQ52 accelerates leaf senescence in Arabidopsis.

Leaf senescence plays an important role in the improvement of maize kernel yields. However, the underlying regulatory mechanisms of leaf senescence in maize are largely unknown. We isolated ZmVQ52 and studied the function of ZmVQ52 which encoded, a VQ family transcription factor. ZmVQ52 is constitutively expressed in maize tissues, and mainly expressed in the leaf; it is located in the nucleus of maize protoplasts. Four WRKY family proteins-ZmWRKY20, ZmWRKY36, ZmWRKY50, and ZmWRKY71-were identified as interacting with ZmVQ52. The overexpression of ZmVQ52 in Arabidopsis accelerated premature leaf senescence. The leaf of the ZmVQ52-overexpression line showed a lower chlorophyll content and higher senescence rate than the WT. A number of leaf senescence regulating genes were up-regulated in the ZmVQ52-overexpression line. Additionally, hormone treatments revealed that the leaf of the ZmVQ52-overexpressed line was more sensitive to salicylic acid (SA) and jasmonic acid (JA), and had an enhanced tolerance to abscisic acid (ABA). Moreover, a transcriptome analysis of the ZmVQ52-overexpression line revealed that ZmVQ52 is mainly involved in the circadian pathway and photosynthetic pathways.

Correction: Overexpression of a maize plasma membrane intrinsic protein ZmPIP1;1 confers drought and salt tolerance in Arabidopsis.

[This corrects the article DOI: 10.1371/journal.pone.0198639.].

Arabinose biosynthesis is critical for salt stress tolerance in Arabidopsis.

The capability to maintain cell wall integrity is critical for plants to adapt to unfavourable conditions. l-Arabinose (Ara) is a constituent of several cell wall polysaccharides and many cell wall-localised glycoproteins, but so far the contribution of Ara metabolism to abiotic stress tolerance is still poorly understood. Here, we report that mutations in the MUR4 (also known as HSR8) gene, which is required for the biosynthesis of UDP-Arap in Arabidopsis, led to reduced root elongation under high concentrations of NaCl, KCl, NaNO3 , or KNO3 . The short root phenotype of the mur4/hsr8 mutants under high salinity is rescued by exogenous Ara or gum arabic, a commercial product of arabinogalactan proteins (AGPs) from Acacia senegal. Mutation of the MUR4 gene led to abnormal cell-cell adhesion under salt stress. MUR4 forms either a homodimer or heterodimers with its isoforms. Analysis of the higher order mutants of MUR4 with its three paralogues, MURL, DUR, MEE25, reveals that the paralogues of MUR4 also contribute to the biosynthesis of UDP-Ara and are critical for root elongation. Taken together, our work revealed the importance of the Ara metabolism in salt stress tolerance and also provides new insights into the enzymes involved in the UDP-Ara biosynthesis in plants.

ZmAPRG, an uncharacterized gene, enhances acid phosphatase activity and Pi concentration in maize leaf during phosphate starvation.

KEY MESSAGE: An uncharacterized gene, ZmAPRG, isolated by map-based cloning, enhances acid phosphatase activity and phosphate concentration in maize leaf during phosphate starvation. Acid phosphatase (APase) plays important roles in the absorption and utilization of phosphate (Pi) during maize growth. The information on genes regulating the acid phosphatase activity (APA) in maize leaves remains obscured. In a previous study, we delimited the quantitative trait locus, QTL-AP9 for APA to a region of about 546 kb. Here, we demonstrate that the GRMZM2G041022 located in the 546 kb region is a novel acid phosphatase-regulating gene (ZmAPRG). Its overexpression significantly increased the APA and Pi concentration in maize and rice leaves. Subcellular localization of ZmAPRG showed that it was anchored on the plasma and nuclear membrane. The transcriptome analysis of maize ZmAPRG overexpressing lines (ZmAPRG OE) revealed 1287 up-regulated and 392 down-regulated genes. Among these, we found APase, protein phosphatase, and phosphate transporter genes, which are known to be implicated in the metabolism and utilization of Pi. We inferred the ZmAPRG functions as an upstream regulation node, directly or indirectly regulating APases, protein phosphatases, and phosphate transporter genes involved in Pi metabolism and utilization in maize. These findings will pave the way for elucidating the mechanism of APase regulation, absorption and utilization of Pi, and would facilitate maize breeding for efficient use of fertilizers.

Overexpression of a maize plasma membrane intrinsic protein ZmPIP1;1 confers drought and salt tolerance in Arabidopsis.

Drought and salt stress are major abiotic stress that inhibit plants growth and development, here we report a plasma membrane intrinsic protein ZmPIP1;1 from maize and identified its function in drought and salt tolerance in Arabidopsis. ZmPIP1;1 was localized to the plasma membrane and endoplasmic reticulum in maize protoplasts. Treatment with PEG or NaCl resulted in induced expression of ZmPIP1;1 in root and leaves. Constitutive overexpression of ZmPIP1;1 in transgenic Arabidopsis plants resulted in enhanced drought and salt stress tolerance compared to wild type. A number of stress responsive genes involved in cellular osmoprotection in ZmPIP1;1 overexpression plants were up-regulated under drought or salt condition. ZmPIP1;1 overexpression plants showed higher activities of reactive oxygen species (ROS) scavenging enzymes such as catalase and superoxide dismutase, lower contents of stress-induced ROS such as superoxide, hydrogen peroxide and malondialdehyde, and higher levels of proline under drought and salt stress than did wild type. ZmPIP1;1 may play a role in drought and salt stress tolerance by inducing of stress responsive genes and increasing of ROS scavenging enzymes activities, and could provide a valuable gene for further plant breeding.

Identification and characterization of paternal-preferentially expressed gene NF-YC8 in maize endosperm.

Gene imprinting describes an epigenetic phenomenon, whereby genetically identical alleles are differentially expressed dependent on parent-of-origin. Some imprinted genes belonged to NUCLEAR FACTOR Y (NF-Y) transcription factors, which were involved in many important metabolic processes in plant. The characterizations of imprinted genes are of great importance for their function exploration. In this paper, 15 non-redundant NF-YC genes were identified in the maize genome and the paternally expressed gene NF-YC8 was further analyzed. NF-YC8 primarily expressed in maize immature ear and tassel and phylogenetic analysis showed that NF-YC8 was highly homologous with Arabidopsis thaliana NF-YC2 genes which function in regulation of the flowering processes, ER stress response. Furthermore, NF-YC8 was a differential, gene-specific imprinted gene at 14 DAP and persistently imprinted throughout later endosperm development in the B73/Mo17 genetic background. Bisulfite sequencing for NF-YC8 in maize endosperm showed that the paternal alleles were higher methylated (CG, CHG and CHH contexts) than maternal alleles in the 5' upstream region, and the coding region was highly methylated in CG context. Additionally, TE (CG, CHG and CHH contexts) and repetitive region (CG and CHG contexts) were all highly methylated. These results are the first description of evolution and molecular characterization of maize NF-YC8 and will provide new references for maize NF-YC genetic analysis.

Characterization, fine mapping and expression profiling of Ragged leaves1 in maize.

The Ragged leaves1 (Rg1) maize mutant frequently develops lesions on leaves, leaf sheaths, and ear bracts. Lesion formation is independent of biotic stress. High-level accumulation of H(2)O(2) revealed by staining Rg1 leaves, with 3',3'-diaminobenzidine and trypan blue, suggested that lesion formation appeared to be due to cell death. Rg1 was initially mapped to an interval around 70.5 Mb in bin 3.04 on the short arm of chromosome 3. Utilizing 15 newly developed markers, Rg1 was delimitated to an interval around 17 kb using 16,356 individuals of a BC1 segregating population. There was only one gene, rp3, predicted in this region according to the B73 genome. Analysis of transcriptome data revealed that 441 genes significantly up-regulated in Rg1 leaves were functionally over-represented. Among those genes, several were involved in the production of reactive oxygen species (ROS). Our results suggested that lesions of Rg1 maize arose probably due to an aberrant rust resistance allele of Rp3, which elicited the accumulation of ROS independent of biotic stress.

Identification and fine mapping of rhm1 locus for resistance to Southern corn leaf blight in maize.

rhm1 is a major recessive disease resistance locus for Southern corn leaf blight (SCLB). To further narrow down its genetic position, F(2) population and BC(1) F(1) population derived from the cross between resistant (H95(rhm) ) and susceptible parents (H95) of maize (Zea mays) were constructed. Using newly developed markers, rhm1 was initially delimited within an interval of 2.5 Mb, and then finally mapped to a 8.56 kb interval between InDel marker IDP961-503 and simple sequence repeat (SSR) marker A194149-1. Three polymorphic markers IDP961-504, IDP B2-3 and A194149-2 were shown to be co-segregated with the rhm1 locus. Sequence analysis of the 8.56 kb DNA fragment revealed that it contained only one putative gene with a predicted amino acid sequence identical to lysine histidine transporter 1 (LHT1). Comparative sequence analysis indicated that the LHT1 in H95(rhm) harbors a 354 bp insertion in its third exon as compared with that of susceptible alleles in B73, H95 and Mo17. The 354 bp insertion resulted in a truncation of the predicted protein of candidate resistance allele (LHT1-H95(rhm) ). Our results strongly suggest LHT1 as the candidate gene for rhm1 against SCLB. The tightly linked molecular markers developed in this study can be directly used for molecular breeding of resistance to Southern corn leaf blight in maize.