ZmNF-YA1 Contributes to Maize Thermotolerance by Regulating Heat Shock Response.

Zea mays (maize) is a staple food, feed, and industrial crop. Heat stress is one of the major stresses affecting maize production and is usually accompanied by other stresses, such as drought. Our previous study identified a heterotrimer complex, ZmNF-YA1-YB16-YC17, in maize. ZmNF-YA1 and ZmNF-YB16 were positive regulators of the drought stress response and were involved in maize root development. In this study, we investigated whether ZmNF-YA1 confers heat stress tolerance in maize. The nf-ya1 mutant and overexpression lines were used to test the role of ZmNF-YA1 in maize thermotolerance. The nf-ya1 mutant was more temperature-sensitive than the wild-type (WT), while the ZmNF-YA1 overexpression lines showed a thermotolerant phenotype. Higher malondialdehyde (MDA) content and reactive oxygen species (ROS) accumulation were observed in the mutant, followed by WT and overexpression lines after heat stress treatment, while an opposite trend was observed for chlorophyll content. RNA-seq was used to analyze transcriptome changes in nf-ya1 and its wild-type control W22 in response to heat stress. Based on their expression profiles, the heat stress response-related differentially expressed genes (DEGs) in nf-ya1 compared to WT were grouped into seven clusters via k-means clustering. Gene Ontology (GO) enrichment analysis of the DEGs in different clades was performed to elucidate the roles of ZmNF-YA1-mediated transcriptional regulation and their contribution to maize thermotolerance. The loss function of ZmNF-YA1 led to the failure induction of DEGs in GO terms of protein refolding, protein stabilization, and GO terms for various stress responses. Thus, the contribution of ZmNF-YA1 to protein stabilization, refolding, and regulation of abscisic acid (ABA), ROS, and heat/temperature signaling may be the major reason why ZmNF-YA1 overexpression enhanced heat tolerance, and the mutant showed a heat-sensitive phenotype.

Transcription factors ZmNF-YA1 and ZmNF-YB16 regulate plant growth and drought tolerance in maize.

The identification of drought stress regulatory genes is crucial for the genetic improvement of maize (Zea mays L.) yield. Nuclear factors Y (NF-Ys) are important transcription factors, but their roles in the drought stress tolerance of plants and underlying molecular mechanisms are largely unknown. In this work, we used yeast two-hybrid screening to identify potential interactors of ZmNF-YB16 and confirmed the interaction between ZmNF-YA1 and ZmNF-YB16-YC17 and between ZmNF-YA7 and ZmNF-YB16-YC17. ZmNF-YB16 interacted with ZmNF-YC17 via its histone fold domain to form a heterodimer in the cytoplasm and then entered the nucleus to form a heterotrimer with ZmNF-YA1 or ZmNF-YA7 under osmotic stress. Overexpression of ZmNF-YA1 improved drought and salt stress tolerance and root development of maize, whereas zmnf-ya1 mutants exhibited drought and salt stress sensitivity. ZmNF-YA1-mediated transcriptional regulation, especially in JA signaling, histone modification, and chromatin remodeling, could underlie the altered stress tolerance of zmnf-ya1 mutant plants. ZmNF-YA1 bound to promoter CCAAT motifs and directly regulated the expression of multiple genes that play important roles in stress responses and plant development. Comparison of ZmNF-YB16- and ZmNF-YA1-regulated genes showed that ZmNF-YA1 and ZmNF-YB16 have similar biological functions in stress responses but varied functions in other biological processes. Taken together, ZmNF-YA1 is a positive regulator of plant drought and salt stress responses and is involved in the root development of maize, and ZmNF-Y complexes with different subunits may have discrepant functions.

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.

TsHD1 and TsNAC1 cooperatively play roles in plant growth and abiotic stress resistance of Thellungiella halophile.

T. HALOPHILA HOMEOBOX PROTEIN 1(TsHD1) cloned from the halophyte Thellungiella halophila is a homeodomain (HD) transcription factor gene and functions as a collaborator of TsNAC1. TsHD1 can form heterodimers with TsNAC1 via the interaction between its zinc finger (ZF) domain and the A subdomain of TsNAC1. The overexpression of TsHD1 improved the heat stress resistance of T. halophila and retarded its vegetative growth slightly. The co-overexpression of TsHD1 and TsNAC1 highly improved heat and drought stress resistance by increasing the accumulation of heat shock proteins and enhancing the expression levels of drought stress response genes, such as MYB DOMAIN PROTEIN 77 and MYB DOMAIN PROTEIN 96 (MYB77and MYB96) and SALT TOLERANCE ZINC FINGER 10 and SALT TOLERANCE ZINC FINGER 18 (ZAT10 and ZAT18), but seriously retarded the vegetative growth of T. halophila by restraining cell expansion. The heterodimer of TsHD1 and TsNAC1 has higher transcriptional activation activity and higher stability compared with the homodimer of TsHD1 or TsNAC1. The binding sites of the TsHD1 and TsNAC1 heterodimers were found to exist in the promoters of most upregulated genes in Cauliflower mosaic virus 35S promoter (P35S)::TsHD1 and P35S::TsNAC1 transgene lines compared with the wild type using RNA-seq and genomic data analyses. Moreover, the binding sites in the promoter region of the most downregulated genes were located in the vicinity of the TATA-box. This study reveals that TsNAC1 and TsHD1 play roles in plant growth and abiotic stress resistance synergistically, and the effects depend on the heterodimer binding to the specific target sites in the promoter region.

Effects of maize organ-specific drought stress response on yields from transcriptome analysis.

BACKGROUND: Drought is a serious causal factor of reduced crop yields than any other abiotic stresses. As one of the most widely distributed crops, maize plants frequently suffer from drought stress, which causes great losses in the final kernel yield. Drought stress response in plants showed tissue- and developmental stage-specific characteristics. RESULTS: In this study, the ears at the V9 stage, kernels and ear leaf at the 5DAP (days after pollination) stage of maize were used for morphological, physiological and comparative transcriptomics analysis to understand the different features of "sink" or "source" organs and the effects on kernel yield under drought stress conditions. The ABA-, NAC-mediate signaling pathway, osmotic protective substance synthesis and protein folding response were identified as common drought stress response in the three organs. Tissue-specific drought stress responses and the regulators were identified, they were highly correlated with growth, physiological adaptation and yield loss under drought stress. For ears, drought stress inhibited ear elongation, led to the abnormal differentiation of the paired spikelet, and auxin signaling involved in the regulation of cell division and growth and primordium development changes. In the kernels, reduced kernel size caused by drought stress was observed, and the obvious differences of auxin, BR and cytokine signaling transduction appeared, which indicated the modification in carbohydrate metabolism, cell differentiation and growth retardation. For the ear leaf, dramatically and synergistically reduced the expression of photosynthesis genes were observed when suffered from drought stress, the ABA- and NAC- mediate signaling pathway played important roles in the regulation of photosynthesis. CONCLUSIONS: Transcriptomic changes caused by drought were highly correlated with developmental and physiological adaptation, which was closely related to the final yield of maize, and a sketch of tissue- and developmental stage-specific responses to drought stress in maize was drafted.

TsNAC1 Is a Key Transcription Factor in Abiotic Stress Resistance and Growth.

NAC proteins constitute one of the largest families of plant-specific transcription factors, and a number of these proteins participate in the regulation of plant development and responses to abiotic stress. T. HALOPHILA STRESS RELATED NAC1 (TsNAC1), cloned from the halophyte Thellungiella halophila, is a NAC transcription factor gene, and its overexpression can improve abiotic stress resistance, especially in salt stress tolerance, in both T. halophila and Arabidopsis (Arabidopsis thaliana) and retard the growth of these plants. In this study, the transcriptional activation activity of TsNAC1 and RD26 from Arabidopsis was compared with the target genes' promoter regions of TsNAC1 from T. halophila, and the results showed that the transcriptional activation activity of TsNAC1 was higher in tobacco (Nicotiana tabacum) and yeast. The target sequence of the promoter from the target genes also was identified, and TsNAC1 was shown to target the positive regulators of ion transportation, such as T. HALOPHILA H+-PPASE1, and the transcription factors MYB HYPOCOTYL ELONGATION-RELATED and HOMEOBOX12 In addition, TsNAC1 negatively regulates the expansion of cells, inhibits LIGHT-DEPENDENT SHORT HYPOCOTYLS1 and UDP-XYLOSYLTRANSFERASE2, and directly controls the expression of MULTICOPY SUPPRESSOR OF IRA14 Based on these results, we propose that TsNAC1 functions as an important upstream regulator of plant abiotic stress responses and vegetative growth.

ZmbZIP4 Contributes to Stress Resistance in Maize by Regulating ABA Synthesis and Root Development.

In plants, bZIP (basic leucine zipper) transcription factors regulate diverse processes such as development and stress responses. However, few of these transcription factors have been functionally characterized in maize (Zea mays). In this study, we characterized the bZIP transcription factor gene ZmbZIP4 from maize. ZmbZIP4 was differentially expressed in various organs of maize and was induced by high salinity, drought, heat, cold, and abscisic acid treatment in seedlings. A transactivation assay in yeast demonstrated that ZmbZIP4 functioned as a transcriptional activator. A genome-wide screen for ZmbZIP4 targets by immunoprecipitation sequencing revealed that ZmbZIP4 could positively regulate a number of stress response genes, such as ZmLEA2, ZmRD20, ZmRD21, ZmRab18, ZmNHX3, ZmGEA6, and ZmERD, and some abscisic acid synthesis-related genes, including NCED, ABA1, AAO3, and LOS5 In addition, ZmbZIP4 targets some root development-related genes, including ZmLRP1, ZmSCR, ZmIAA8, ZmIAA14, ZmARF2, and ZmARF3, and overexpression of ZmbZIP4 resulted in an increased number of lateral roots, longer primary roots, and an improved root system. Increased abscisic acid synthesis by overexpression of ZmbZIP4 also can increase the plant's ability to resist abiotic stress. Thus, ZmbZIP4 is a positive regulator of plant abiotic stress responses and is involved in root development in maize.

The bHLH family member ZmPTF1 regulates drought tolerance in maize by promoting root development and abscisic acid synthesis.

Drought stress is the most important environmental stress limiting maize production. ZmPTF1, a phosphate starvation-induced basic helix-loop-helix (bHLH) transcription factor, contributes to root development and low-phosphate tolerance in maize. Here, ZmPTF1 expression, drought tolerance, and the underlying mechanisms were studied by using maize ZmPTF1 overexpression lines and mutants. ZmPTF1 was found to be a positive regulator of root development, ABA synthesis, signalling pathways, and drought tolerance. ZmPTF1 was also found to bind to the G-box element within the promoter of 9-cis-epoxycarotenoid dioxygenase (NCED), C-repeat-binding factor (CBF4), ATAF2/NAC081, NAC30, and other transcription factors, and to act as a positive regulator of the expression of those genes. The dramatically upregulated NCEDs led to increased abscisic acid (ABA) synthesis and activation of the ABA signalling pathway. The up-regulated transcription factors hierarchically regulate the expression of genes involved in root development, stress responses, and modifications of transcriptional regulation. The improved root system, increased ABA content, and activated ABA-, CBF4-, ATAF2-, and NAC30-mediated stress responses increased the drought tolerance of the ZmPTF1 overexpression lines, while the mutants showed opposite trends. This study describes a useful gene for transgenic breeding and helps us understand the role of a bHLH protein in plant root development and stress responses.

Over-expression of mutated ZmDA1 or ZmDAR1 gene improves maize kernel yield by enhancing starch synthesis.

Grain weight and grain number are important crop yield determinants. DA1 and DAR1 are the ubiquitin receptors that function as the negative regulators of cell proliferation during development in Arabidopsis. An arginine to lysine mutant at amino acid site 358 could lead to the da1-1 phenotype, which results in an increased organ size and larger seeds. In this study, the mutated ZmDA1 (Zmda1) and mutated ZmDAR1 (Zmdar1) driven by the maize ubiquitin promoter were separately introduced into maize elite inbred line DH4866. The grain yield of the transgenic plants was 15% greater than that of the wild-type in 3 years of field trials due to improvements in the grain number, weight and starch content. Interestingly, the over-expression of Zmda1 and Zmdar1 promoted kernel development, resulting in a more developed basal endosperm transfer cell layer (BETL) than WT and enhanced expression of starch synthase genes. This study suggests that the over-expression of the mutated ZmDA1 or ZmDAR1 genes improves the sugar imports into the sink organ and starch synthesis in maize kernels.

Enhancing auxin accumulation in maize root tips improves root growth and dwarfs plant height.

Maize is a globally important food, feed crop and raw material for the food and energy industry. Plant architecture optimization plays important roles in maize yield improvement. PIN-FORMED (PIN) proteins are important for regulating auxin spatiotemporal asymmetric distribution in multiple plant developmental processes. In this study, ZmPIN1a overexpression in maize increased the number of lateral roots and inhibited their elongation, forming a developed root system with longer seminal roots and denser lateral roots. ZmPIN1a overexpression reduced plant height, internode length and ear height. This modification of the maize phenotype increased the yield under high-density cultivation conditions, and the developed root system improved plant resistance to drought, lodging and a low-phosphate environment. IAA concentration, transport capacity determination and application of external IAA indicated that ZmPIN1a overexpression led to increased IAA transport from shoot to root. The increase in auxin in the root enabled the plant to allocate more carbohydrates to the roots, enhanced the growth of the root and improved plant resistance to environmental stress. These findings demonstrate that maize plant architecture can be improved by root breeding to create an ideal phenotype for further yield increases.

Structural, expression and evolutionary analysis of the non-specific phospholipase C gene family in Gossypium hirsutum.

BACKGROUND: Nonspecific phospholipase C (NPC), which belongs to a phospholipase C subtype, is a class of phospholipases that hydrolyzes the primary membrane phospholipids, such as phosphatidylcholine, to yield sn-1, 2-diacylglycerol and a phosphorylated head-group. NPC plays multiple physiological roles in lipid metabolism and signaling in plants. To fully understand the putative roles of NPC genes in upland cotton, we cloned NPC genes from Gossypium hirsutum and carried out structural, expression and evolutionary analysis. RESULTS: Eleven NPC genes were cloned from G. hirsutum, which were found on chromosomes scaffold269.1, D03, A07, D07, A08, D11, and scaffold3511_A13. All GhNPCs had typical phosphoesterase domains and have hydrolase activity that acts on ester bonds. GhNPCs were annotated as phospholipase C, which was involved in glycerophospholipid metabolism, ether lipid metabolism, and biosynthesis of secondary metabolites. These GhNPCs showed differential expression patterns in distinct plant tissues and in response to various types of stress (low-phosphate, salt, drought, and abscisic acid). They also had different types and numbers of cis-element. GhNPCs could be classified into four subfamilies. Four pairs of GhNPCs were generated by whole-genome duplication and they underwent purifying selection. CONCLUSIONS: Our results suggested that GhNPCs are involved in regulating key abiotic stress responses and ABA signaling transduction, and they may have various functional roles for different members under complex abiotic stress conditions. Functional divergence may be the evolutionary driving force for the retention of four pairs of duplicate NPCs. Our analysis provides a solid foundation for the further functional characterization of the GhNPC gene family, and leads to potential applications in the genetic improvement of cotton cultivars.

Physiological and comparative proteome analyses reveal low-phosphate tolerance and enhanced photosynthesis in a maize mutant owing to reinforced inorganic phosphate recycling.

BACKGROUND: The low-phosphate-tolerant maize mutant Qi319-96 was obtained from Qi319 through cellular engineering. To elucidate the molecular mechanisms underlying the low-phosphate tolerance of this mutant, we performed comparative proteome analyses of the leaves of Qi319-96 and Qi319 under inorganic phosphate (Pi)-sufficient and Pi-deficient conditions. RESULTS: Low-phosphorus levels limit plant growth and metabolism. Although the overall phosphorus contents of shoots were not significantly different between Qi319 and Qi319-96, the Pi level of Qi319-96 was 52.94 % higher than that of Qi319. Under low phosphorus conditions, Qi319-96 had increased chlorophyll levels and enhanced photosynthesis. The changes in starch and sucrose contents under these conditions also differed between genotypes. The proteomic changes included 29 (Pi-sufficient) and 71 (Pi-deficient) differentially expressed proteins involved in numerous metabolic processes. Proteome and physiological analyses revealed that Qi319-96 could better remodel the lipid composition of membranes and had higher V-ATPase activity levels than Qi319 under low-phosphate starvation, which enhanced the recycling of intracellular Pi, as reflected by its increased Pi levels. Chlorophyll biosynthesis was improved and the levels, and activities, of several Calvin cycle and "CO2 pump" enzymes were greater in Qi319-96 than in Qi319, which led to a higher rate of photosynthesis under low-phosphate stress in this line compared with in Qi319. CONCLUSIONS: Our results suggest that the increased tolerance of the maize mutant Qi319-96 to low-phosphate levels is owing to its ability to increase Pi availability. Additionally, inbred lines of maize with low-P-tolerant traits could be obtained effectively through cellular engineering.

Reduced expression of starch branching enzyme IIa and IIb in maize endosperm by RNAi constructs greatly increases the amylose content in kernel with nearly normal morphology.

MAIN CONCLUSION: RNAi technology was applied to suppress the expression of starch branching enzyme IIa and IIb and to increase amylose content in maize endosperm, and stably inherited high-amylose maize lines were obtained. Amylose is an important material for industries and in the human diet. Maize varieties with endosperm amylose content (AC) of greater than 50 % are termed amylomaize, and possess high industrial application value. The high-amylose trait is controlled by multi-enzyme reaction and intricate gene-environment interaction. Starch branching enzymes are key factors for regulating the branching profiles of starches. In this paper, we report the successful application of RNAi technology for improving amylose content in maize endosperm through the suppression of the ZmSBEIIa and ZmSBEIIb genes by hairpin SBEIIRNAi constructs. These SBEIIRNAi transgenes led to the down-regulation of ZmSBEII expression and SBE activity to various degrees and altered the morphology of starch granules. Transgenic maize lines with AC of up to 55.89 % were produced, which avoided the significant decreases in starch content and grain yield that occur in high-amylose ae mutant. Novel maize lines with high AC offer potential benefits for high-amylose maize breeding. A comparison of gene silencing efficiency among transgenic lines containing different hpSBEIIRNA constructs demonstrated that (1) it was more efficient to use both ZmSBEIIa and ZmSBEIIb specific regions than to use the conserved domain as the inverted repeat arms; (2) the endosperm-specific promoter of the 27-kDa γ-zein provided more efficient inhibition than the CaMV 35S promoter; and (3) inclusion of the catalase intron in the hpSBEIIRNA constructs provided a better silencing effect than the chalcone synthase intron in the hpRNA construct design for suppression of the SBEII subfamily in endosperm.

Overexpression of the phosphatidylinositol synthase gene (ZmPIS) conferring drought stress tolerance by altering membrane lipid composition and increasing ABA synthesis in maize.

Phosphatidylinositol (PtdIns) synthase is a key enzyme in the phospholipid pathway and catalyses the formation of PtdIns. PtdIns is not only a structural component of cell membranes, but also the precursor of the phospholipid signal molecules that regulate plant response to environment stresses. Here, we obtained transgenic maize constitutively overexpressing or underexpressing PIS from maize (ZmPIS) under the control of a maize ubiquitin promoter. Transgenic plants were confirmed by PCR, Southern blotting analysis and real-time RT-PCR assay. The electrospray ionization tandem mass spectrometry (ESI-MS/MS)-based lipid profiling analysis showed that, under drought stress conditions, the overexpression of ZmPIS in maize resulted in significantly elevated levels of most phospholipids and galactolipids in leaves compared with those in wild type (WT). At the same time, the expression of some genes involved in the phospholipid metabolism pathway and the abscisic acid (ABA) biosynthesis pathway including ZmPLC, ZmPLD, ZmDGK1, ZmDGK3, ZmPIP5K9, ZmABA1, ZmNCED, ZmAAO1, ZmAAO2 and ZmSCA1 was markedly up-regulated in the overexpression lines after drought stress. Consistent with these results, the drought stress tolerance of the ZmPIS sense transgenic plants was enhanced significantly at the pre-flowering stages compared with WT maize plants. These results imply that ZmPIS regulates the plant response to drought stress through altering membrane lipid composition and increasing ABA synthesis in maize.

Phosphate starvation of maize inhibits lateral root formation and alters gene expression in the lateral root primordium zone.

BACKGROUND: Phosphorus (P) is an essential macronutrient for all living organisms. Maize (Zea mays) is an important human food, animal feed and energy crop throughout the world, and enormous quantities of phosphate fertilizer are required for maize cultivation. Thus, it is important to improve the efficiency of the use of phosphate fertilizer for maize. RESULTS: In this study, we analyzed the maize root response to phosphate starvation and performed a transcriptomic analysis of the 1.0-1.5 cm lateral root primordium zone. In the growth of plants, the root-to-shoot ratio (R/L) was reduced in both low-phosphate (LP) and sufficient-phosphate (SP) solutions, but the ratio (R/L) exhibited by the plants in the LP solution was higher than that of the SP plants. The growth of primary roots was slightly promoted after 6 days of phosphate starvation, whereas the numbers of lateral roots and lateral root primordia were significantly reduced, and these differences were increased when associated with the stress caused by phosphate starvation. Among the results of a transcriptomic analysis of the maize lateral root primordium zone, there were two highlights: 1) auxin signaling participated in the response and the modification of root morphology under low-phosphate conditions, which may occur via local concentration changes due to the biosynthesis and transport of auxin, and LOB domain proteins may be an intermediary between auxin signaling and root morphology; and 2) the observed retardation of lateral root development was the result of co-regulation of DNA replication, transcription, protein synthesis and degradation and cell growth. CONCLUSIONS: These results indicated that maize roots show a different growth pattern than Arabidopsis under low-phosphate conditions, as the latter species has been observed to halt primary root growth when the root tip comes into contact with low-phosphate media. Moreover, our findings enrich our understanding of plant responses to phosphate deficits and of root morphogenesis in maize.

Overexpression of the phosphatidylinositol synthase gene from Zea mays in tobacco plants alters the membrane lipids composition and improves drought stress tolerance.

Phosphatidylinositol (PtdIns) is an important lipid because it serves as a key membrane constituent and is the precursor of the inositol-containing lipids that are found in all plants and animals. It is synthesized from cytidine-diphosphodiacylglycerol (CDP-DG) and myo-inositol by PtdIns synthase (PIS). We have previously reported that two putative PIS genes from maize (Zea mays L.), ZmPIS and ZmPIS2, are transcriptionally up-regulated in response to drought (Sui et al., Gene, 426:47-56, 2008). In this work, we report on the characterization of ZmPIS in vitro and in vivo. The ZmPIS gene successfully complemented the yeast pis mutant BY4743, and the determination of PIS activity in the yeast strain further confirmed the enzymatic function of ZmPIS. An ESI-MS/MS-based lipid profiling approach was used to identify and quantify the lipid species in transgenic and wild-type tobacco plants before and after drought treatment. The results show that the overexpression of ZmPIS significantly increases lipid levels in tobacco leaves under drought stress compared to those of wild-type tobacco, which correlated well with the increased drought tolerance of the transgenic plants. Further analysis showed that, under drought stress conditions, ZmPIS overexpressors were found to exhibit increased membrane integrity, thereby enabling the retention of more solutes and water compared with the wild-type and the vector control transgenic lines. Our findings give us new insights into the role of the ZmPIS gene in the response of maize to drought/osmotic stress and the mechanisms by which plants adapt to drought stress.

Mapping quantitative trait loci conferring resistance to rice black-streaked virus in maize (Zea mays L.).

Maize rough dwarf disease (MRDD) is one of the most serious virus diseases of maize worldwide, and it causes great reduction of maize production. In China, the pathogen was shown to be rice black-streaked virus (RBSDV). Currently, MRDD has spread broadly and leads to significant loss in China. However, there has been little research devoted to this disease. Our aims were to identify the markers and loci underlying resistance to this virus disease. In this study, segregation populations were constructed from two maize elite lines '90110', which is highly resistant to MRDD and 'Ye478', which is highly susceptible to MRDD. The F(2) and BC(1) populations were used for bulk sergeant analysis (BSA) to identify resistance-related markers. One hundred and twenty F(7:9) RILs were used for quantitative trait loci (QTL) mapping through the experiment of multiple environments over 3 years. Natural occurrence and artificial inoculation were both used and combined to determine the phenotype of plants. Five QTL, qMRD2, qMRD6, qMRD7, qMRD8 and qMRD10 were measured in the experiments. The qMRD8 on chromosome 8 was proved to be one major QTL conferring resistance to RBSDV disease in almost all traits and environments, which explained 12.0-28.9 % of the phenotypic variance for disease severity in this present study.

Effects of Raised Ambient Temperature on the Local and Systemic Adaptions of Maize.

Maize is a staple food, feed, and industrial crop. One of the major stresses on maize production is heat stress, which is usually accompanied by other stresses, such as drought or salinity. In this review, we compared the effects of high temperatures on maize production in China. Heat stress disturbs cellular homeostasis and impedes growth and development in plants. Plants have evolved a variety of responses to minimize the damage related to high temperatures. This review summarized the responses in different cell organelles at elevated temperatures, including transcriptional regulation control in the nuclei, unfolded protein response and endoplasmic reticulum-associated protein quality control in the endoplasmic reticulum (ER), photosynthesis in the chloroplast, and other cell activities. Cells coordinate their activities to mediate the collective stresses of unfavorable environments. Accordingly, we evaluated heat stress at the local and systemic levels in in maize. We discussed the physiological and morphological changes in sensing tissues in response to heat stress in maize and the existing knowledge on systemically acquired acclimation in plants. Finally, we discussed the challenges and prospects of promoting corn thermotolerance by breeding and genetic manipulation.

Over-expression of AGPase genes enhances seed weight and starch content in transgenic maize.

Cereal crops accumulate starch in the seed endosperm as an energy reserve. ADP-glucose pyrophosphorylase (AGPase) plays a key role in regulating starch biosynthesis in cereal seeds. The AGPase in the maize endosperm is a heterotetramer of two small subunits, encoded by Brittle2 (Bt2) gene, and two large subunits, encoded by the Shrunken2 (Sh2) gene. The two genes (Bt2, Sh2) from maize were introduced into two elite maize inbred lines, solely and in tandem, and under the control of endosperm-specific promoters for over-expression. PCR, Southern blotting, and real-time RT-PCR analysis indicated that the transgenes were integrated into the genome of transgenic plants and were over-expressed in their progeny. The over-expression of either gene enhanced AGPase activity, seed weight and starch content compared with the WT, but the amounts were lower than plants with over-expression of both Bt2 and Sh2. Developing seeds from co-expression transgenic maize plants had higher cytoplasmic AGPase activity: the 100-grain weight increased 15% over the wild type (WT), and the starch content increased to over 74% compared with the WT of 65%. These results indicate that over-expression of the genes in transgenic maize plants could improve kernel traits. This report provides a feasible approach for increasing starch content and seed weight in maize.

Overexpression of transcription factor ZmPTF1 improves low phosphate tolerance of maize by regulating carbon metabolism and root growth.

A bHLH (basic helix-loop-helix domain) transcription factor involved in tolerance to Pi starvation was cloned from Zea mays with an RT-PCR coupled RACE approach and named ZmPTF1. ZmPTF1 encoded a putative protein of 481 amino acids that had identity with OsPTF1 in basic region. Real-time RT-PCR revealed that ZmPTF1 was quickly and significantly up-regulated in the root under phosphate starvation conditions. Overexpression of ZmPTF1 in maize improved root development, enhanced biomass both in hydroponic cultures and sand pots, and the plants developed more tassel branches and larger kernels when they were grown in low phosphate soil. Compared with wild type, overexpressing ZmPTF1 altered the concentrations of soluble sugars in transgenic plants, in which soluble sugars levels were lower in the leaves and higher in the roots. Overexpression of ZmPTF1 enhanced the expression of fructose-1,6-bisphosphatase and sucrose phosphate synthase1 participated in sucrose synthesis in the leaves but decreased them in the root, and reduced the expression of genes involved in sucrose catabolism in the roots. The modifications on the physiology and root morphology of the plants enhanced low phosphate tolerance and increased the yield under low phosphate conditions. This research provides a useful gene for transgenic breeding of maize that is tolerant to phosphate deficiency and is helpful for exploring the relationship between sugar signaling and phosphate concentrations in cells.