Systematic analysis of the Rboh gene family in seven gramineous plants and its roles in response to arbuscular mycorrhizal fungi in maize.

BACKGROUND: Plant respiratory burst oxidase homolog (Rboh) gene family produces reactive oxygen species (ROS), and it plays key roles in plant-microbe interaction. Most Rboh gene family-related studies mainly focused on dicotyledonous plants; however, little is known about the roles of Rboh genes in gramineae. RESULTS: A total of 106 Rboh genes were identified in seven gramineae species, including Zea mays, Sorghum bicolor, Brachypodium distachyon, Oryza sativa, Setaria italica, Hordeum vulgare, and Triticum aestivum. The Rboh protein sequences showed high similarities, suggesting that they may have conserved functions across different species. Duplication mode analysis detected whole-genome/segmental duplication (WGD)/(SD) and dispersed in the seven species. Interestingly, two local duplication (LD, including tandem and proximal duplication) modes were found in Z. mays, S. italica and H. vulgare, while four LD were detected in T. aestivum, indicating that these genes may have similar functions. Collinearity analysis indicated that Rboh genes are at a stable evolution state in all the seven species. Besides, Rboh genes from Z. mays were closely related to those from S. bicolor, consistent with the current understanding of plant evolutionary history. Phylogenetic analysis showed that the genes in the subgroups I and II may participate in plant-AM fungus symbiosis. Cis-element analysis showed that different numbers of elements are related to fungal induction in the promoter region. Expression profiles of Rboh genes in Z. mays suggested that Rboh genes had distinct spatial expression patterns. By inoculation with AM fungi, our transcriptome analysis showed that the expression of Rboh genes varies upon AM fungal inoculation. In particularly, ZmRbohF was significantly upregulated after inoculation with AM fungi. pZmRbohF::GUS expression analyses indicated that ZmRbohF was induced by arbuscular mycorrhizal fungi in maize. By comparing WT and ZmRbohF mutant, we found ZmRbohF had limited impact on the establishment of maize-AM fungi symbiosis, but play critical roles in regulating the proper development of arbuscules. CONCLUSIONS: This study provides a comprehensive analysis of the evolution relationship of Rboh genes in seven gramineae species. Results showed that several Rboh genes regulate maize-AM fungal symbiosis process. This study provides valuable information for further studies of Rboh genes in gramineae.

A maize heat shock factor ZmHsf11 negatively regulates heat stress tolerance in transgenic plants.

BACKGROUND: Heat shock transcription factors (Hsfs) are highly conserved among eukaryote and always play vital role in plant stress responses. Whereas, function and mechanism of Hsfs in maize are limited. RESULTS: In this study, an HSF gene ZmHsf11, a member of class B Hsfs, was cloned from maize, and it was up-regulated under heat treatment. ZmHsf11 was a nuclear protein with no transcriptional autoactivation activity in yeast. Overexpression of ZmHsf11 gene in Arabidopsis and rice significantly reduced the survival rate under heat shock treatment and decreased ABA sensitivity of transgenic plants. Under heat stress, transgenic rice accumulated more H2O2, increased cell death, and decreased proline content compared with wild type. In addition, RT-qPCR analysis revealed that ZmHsf11 negatively regulated some oxidative stress-related genes APX2, DREB2A, HsfA2e, NTL3, GR and HSP17 under heat stress treatment. CONCLUSIONS: Our results indicate that ZmHsf11 decreases plant tolerance to heat stress by negatively regulating the expression of oxidative stress-related genes, increasing ROS levels and decreasing proline content. It is a negative regulator involved in high temperature stress response.

Characterization and phylogenetic analysis of multiple C2 domain and transmembrane region proteins in maize.

BACKGROUND: Multiple C2 domain and transmembrane region proteins (MCTPs) are evolutionarily conserved and important signaling molecules. However, the MCTP gene family has not been comprehensively analyzed in maize. RESULTS: In this study, 385 MCTP genes were identified in all surveyed 38 species. Moreover, gene duplication mode exploration showed that whole genome duplication (WGD) mainly contributed to the expansion of MCTP genes in angiosperms. Phylogeny reconstruction with all surveyed species by the maximum-likelihood (ML) method showed five clades of MCTPs, Clades I to V. Each clade of MCTPs had conservative structures and motifs. Focusing on maize, 17 MCTPs were identified, and a neighborjoining (NJ) phylogenetic tree with only ZmMCTPs was also constructed. As expected, 17 MCTPs showed similar phylogenetic relationships in the neighbor-joining (NJ) tree with those in the maximum-likelihood (ML) tree and could also be divided into five subclades. Moreover, ZmMCTP members in different clades showed specific gene structure, conserved motif, and domain structure compositions. Intriguingly, most ZmMCTP genes were intronless. Analyses of isoelectric points (pIs) and grand averages of hydropathicity (GRAVYs) indicated that the N-terminus was more dispersive than the C-terminus. Further tissue-specific expression analysis indicated that duplicated ZmMCTP pairs involved in whole genome duplication (WGD) had similar expression trends. Finally, ZmMCTPs were transcriptionally altered under diverse abiotic stresses and hormone treatments. CONCLUSIONS: Our results contribute to deciphering the evolutionary history of MCTPs in maize and other plants, facilitating further functional analysis of these factors, and provide a basis for further clarification of the molecular mechanism of stress responses.

ZmGLP1, a Germin-like Protein from Maize, Plays an Important Role in the Regulation of Pathogen Resistance.

A gene encoding a protein similar to germin-like proteins (GLPs) was obtained from maize (Zea mays) and designated as ZmGLP1. Based on the ZmGLP1 conserved domain and phylogenetic status, ZmGLP1 was grouped into GLP subfamily b and has high similarity to OsGLP8-14 from Oryza sativa. ZmGLP1 is expressed in different maize tissues during different growth stages and is mainly expressed in the stems and leaves. The induced expression patterns confirmed that ZmGLP1 is differentially expressed under abiotic and hormone stress; it had an early response to jasmonic acid (JA) and ethephon (ET) but a late response to salicylic acid (SA) and was significantly upregulated under Bipolaris maydis infection. The overexpression of ZmGLP1 in Arabidopsis improved the resistance to biotrophic Pseudomonas syringae pv. tomato DC3000 (PstDC3000) and necrotrophic Sclerotinia sclerotiorum by inducing the expression of JA signaling-related genes. Moreover, the hydrogen peroxide (H2O2) content increased due to the overexpression of ZmGLP1 in Arabidopsis after pathogen infection. Compared to the wild-type control, the H2O2 content of ZmGLP1-overexpressing Arabidopsis infected by PstDC3000 increased significantly but was lower in transgenic plants infected with S. sclerotiorum. Furthermore, high-performance liquid chromatography-tandem mass (HPLC-MS/MS) spectrometry showed that the JA contents of ZmGLP1-overexpressing Arabidopsis markedly increased after pathogen infection. However, the improved resistance of ZmGLP1-overexpressing Arabidopsis pretreated with the JA biosynthetic inhibitor, sodium diethyldithiocarbamate trihydrate (DIECA), was suppressed. Based on these findings, we speculate that ZmGLP1 plays an important role in the regulation of Arabidopsis resistance to biotrophic PstDC3000 and necrotrophic S. sclerotiorum; the regulatory effects are achieved by inducing plant oxidative burst activity and activation of the JA signaling pathway.

Identification and Analysis of Stress-Associated Proteins (SAPs) Protein Family and Drought Tolerance of ZmSAP8 in Transgenic Arabidopsis.

Stress-associated proteins (SAPs), a class of A20/AN1 zinc finger proteins, play vital roles in plant stress response. However, investigation of SAPs in maize has been very limited. Herein, to better trace the evolutionary history of SAPs in maize and plants, 415 SAPs were identified in 33 plant species and four species of other kingdoms. Moreover, gene duplication mode exploration showed whole genome duplication contributed largely to SAP gene expansion in angiosperms. Phylogeny reconstruction was performed with all identified SAPs by the maximum likelihood (ML) method and the SAPs were divided into five clades. SAPs within the same clades showed conserved domain composition. Focusing on maize, nine ZmSAPs were identified. Further promoter cis-elements and stress-induced expression pattern analysis of ZmSAPs indicated that ZmSAP8 was a promising candidate in response to drought stress, which was the only AN1-AN1-C2H2-C2H2 type SAP in maize and belonged to clade I. Additionally, ZmSAP8 was located in the nucleus and had no transactivation activity in yeast. Overexpressing ZmSAP8 enhanced the tolerance to drought stress in Arabidopsis thaliana, with higher seed germination and longer root length. Our results should benefit the further functional characterization of ZmSAPs.

A Novel Heat Shock Transcription Factor (ZmHsf08) Negatively Regulates Salt and Drought Stress Responses in Maize.

Heat shock transcription factors (HSFs) play important roles in plant growth, development, and stress responses. However, the function of these transcription factors in abiotic stress responses in maize (Zea mays) remains largely unknown. In this study, we characterized a novel HSF transcription factor gene, ZmHsf08, from maize. ZmHsf08 was highly homologous to SbHsfB1, BdHsfB1, and OsHsfB1, and has no transcriptional activation activity. The expression profiles demonstrated that ZmHsf08 was differentially expressed in various organs of maize and was induced by salt, drought, and abscisic acid (ABA) treatment. Moreover, the overexpression of ZmHsf08 in maize resulted in enhanced sensitivity to salt and drought stresses, displaying lower survival rates, higher reactive oxygen species (ROS) levels, and increased malondialdehyde (MDA) contents compared with wild-type (WT) plants. Furthermore, RT-qPCR analyses revealed that ZmHsf08 negatively regulates a number of stress/ABA-responsive genes under salt and drought stress conditions. Collectively, these results indicate that ZmHsf08 plays a negative role in response to salt and drought stresses in maize.

Expression of Maize MADS Transcription Factor ZmES22 Negatively Modulates Starch Accumulation in Rice Endosperm.

As major component in cereals grains, starch has been one of the most important carbohydrate consumed by a majority of world's population. However, the molecular mechanism for regulation of biosynthesis of starch remains elusive. In the present study, ZmES22, encoding a MADS-type transcription factor, was modestly characterized from maize inbred line B73. ZmES22 exhibited high expression level in endosperm at 10 days after pollination (DAP) and peaked in endosperm at 20 DAP, indicating that ZmES22 was preferentially expressed in maize endosperm during active starch synthesis. Transient expression of ZmES22 in tobacco leaf revealed that ZmES22 protein located in nucleus. No transactivation activity could be detected for ZmES22 protein via yeast one-hybrid assay. Transformation of overexpressing plasmid 35S::ZmES22 into rice remarkedly reduced 1000-grain weight as well as the total starch content, while the soluble sugar was significantly higher in transgenic rice lines. Moreover, overexpressing ZmES22 reduced fractions of long branched starch. Scanning electron microscopy images of transverse sections of rice grains revealed that altered expression of ZmES22 also changed the morphology of starch granule from densely packed, polyhedral starch granules into loosely packed, spherical granules with larger spaces. Furthermore, RNA-seq results indicated that overexpressing ZmES22 could significantly influence mRNA expression levels of numerous key regulatory genes in starch synthesis pathway. Y1H assay illustrated that ZmES22 protein could bind to the promoter region of OsGIF1 and downregulate its mRNA expression during rice grain filling stages. These findings suggest that ZmES22 was a novel regulator during starch synthesis process in rice endosperm.

Whole-Genome and Transposed Duplication Contributes to the Expansion and Diversification of TLC Genes in Maize.

TLC (TRAM/LAG/CRN8) proteins play important roles in ceramide metabolism and mycotoxin resistance. Herein a comparative genomics analysis of TLCs was performed in 31 plant and 3 species from other kingdoms, with an emphasis mainly on maize. TLCs were conserved across kingdoms and expanded in angiosperms, largely due to whole-genome/segmental duplication (WGD/SD) under purifying selection. Phylogeny reconstruction by maximum-likelihood method uncovered five TLC clades, subsequently named as TRAM/LAG, CLN8, PS-TLC, TM136 and TLCD clades. Each clade of TLCs shared specific transmembrane regions and motif composition. Divisions of conserved motifs to subunits may have occurred in TM136-type TLCs. Focusing on maize, five WGD and two DNA-mediated transposed duplication (TD) pairs were discovered, accounting for 61.11% ZmTLCs. Combined with further expression analysis, significant divergence was found in expression patterns between most maize WGD pairs, indicating subfunctionalization or/and neofunctionalization. Moreover, ZmTLC5, a deduced parental copy in a TD pair, was highly induced under FB1 and fungus pathogen injection and exhibited potential capacity to respond to environmental stimuli. Additionally, population genetics analysis showed that ZmTLC10 in the CLN8-clade may have experienced significant positive selection and differentiated between wild and inbred maize populations. Overall, our results help to decipher the evolutionary history of TLCs in maize and plants, facilitating further functional analysis of them.

Selective sweep with significant positive selection serves as the driving force for the differentiation of japonica and indica rice cultivars.

BACKGROUND: Asian cultivated rice (Oryza sativa L.), including japonica and indica, is unarguable the most important crop in Asia as well as worldwide. However, a decisive conclusion of its origination and domestication processes are still lacking. Nowadays, the ever-increasing high-throughput sequencing data of numerous rice samples have provided us new opportunities to get close to the answer of these questions. RESULTS: By compiling 296 whole-genome sequenced rice cultivars and 39 diverse wild rice, two types of domesticated regions (DR-I and DR-II) with strong selective sweep signals between different groups were detected. DR-I regions included 28 blocks which significantly differentiated between japonica and indica subspecies, while DR-II regions were consisted of another 28 blocks which significantly differentiated between wild and cultivated rice, each covered 890 kb and 640 kb, respectively. In-depth analysis suggested that both DR-Is and DR-IIs could have originated from Indo-China Peninsula to southern China, and DR-IIs might be introgressed from indica to japonica. Functional bias with significant positive selection has also been detected in the genes of DR-I, suggesting important role of the selective sweep in differentiation of japonica and indica. CONCLUSIONS: This research promoted a new possible model of the origin of the cultivated rice that DR-Is in japonica and indica maybe independently originated from the divergent wild rice in the Indo-China Peninsula to southern China, and then followed by frequent introgression. Genes with significant positive selection and biased functions were also detected which could play important roles in rice domestication and differentiation processes.

Dissimilar Manifestation of Heterosis in Superhybrid Rice at Early-Tillering Stage under Nutrient-Deficient and Nutrient-Sufficient Condition.

Heterosis has long been exploited for crop breeding; however, the genetic mechanisms, particularly the initial establishment of heterosis during the early vegetative growth phase, remain elusive. The biggest challenge for that is to exclude noise genes from the identified heterosis-related candidates. Herein, we use nutrient-deficient hybrid with no measurable growth heterosis as control. After filtering these irrelevant genes, only 336 differentially expressed genes (DEGs), which is significantly lower than in previous reports, were identified as heterosis-related genes in a superhybrid rice of Liang-You-Pei-Jiu (LYP9) at early-tillering stage. Among the DEGs that could be mapped to quantitative trait loci (QTL), approximately 72.8% could be covered by yield or growth vigor-related QTL, thereby suggesting that our DEGs were reliable and may have potential value to rice breeding. Among the 336 DEGs identified, a majority showed intermediate expression relative to that of its parental lines (i.e. additive effects), particularly, expression was frequently more similar to the paternal line rather than the maternal line (44.1% versus 32.7%); the remaining 27.1% were exclusively up- or down-regulated between the hybrid and either parent. Interestingly, up-regulated genes encoded various enzymes, whereas down-regulated genes were enriched in responses to stress, indicating that hybrids may benefit from both activating metabolism-related pathways and alleviating fitness cost through allelic interactions. Furthermore, a significantly larger proportion of divergent genes and higher nonsynonymous substitutions rates were detected in these DEGs, suggesting a potential contribution to the establishment of heterosis in superhybrid rice LYP9.

Evolutionary analysis of RB/Rpi-blb1 locus in the Solanaceae family.

Late blight caused by the oomycete Phytophthora infestans is one of the most severe threats to potato production worldwide. Numerous studies suggest that the most effective protective strategy against the disease would be to provide potato cultivars with durable resistance (R) genes. However, little is known about the origin and evolutional history of these durable R-genes in potato. Addressing this might foster better understanding of the dynamics of these genes in nature and provide clues for identifying potential candidate R-genes. Here, a systematic survey was executed at RB/Rpi-blb1 locus, an exclusive broad-spectrum R-gene locus in potato. As indicated by synteny analysis, RB/Rpi-blb1 homologs were identified in all tested genomes, including potato, tomato, pepper, and Nicotiana, suggesting that the RB/Rpi-blb1 locus has an ancient origin. Two evolutionary patterns, similar to those reported on RGC2 in Lactuca, and Pi2/9 in rice, were detected at this locus. Type I RB/Rpi-blb1 homologs have frequent copy number variations and sequence exchanges, obscured orthologous relationships, considerable nucleotide divergence, and high non-synonymous to synonymous substitutions (Ka/Ks) between or within species, suggesting rapid diversification and balancing selection in response to rapid changes in the oomycete pathogen genomes. These characteristics may serve as signatures for cloning of late blight resistance genes.

Dynamic evolution of NBS-LRR genes in bread wheat and its progenitors.

Extensive studies have focused on the largest class of disease resistance genes (nucleotide binding site-leucine-rich repeat, NBS-LRR) in various plants. However, no research on the dynamic evolution of these genes in domesticated species and their progenitors has been reported. Recently published genome sequences of bread wheat and its two ancestors provide a good opportunity for comparing NBS-encoding genes between ancestors and their progeny. Over 2000 NBS-encoding genes have been identified in bread wheat, which is the largest number having been reported so far. Compared with other grass species, its two progenitors also contained more NBS-encoding genes, indicating that there was an expansion of these genes in their common ancestor. Interestingly, the inherited relationships of NBS-LRR genes among the bread wheat and its two progenitors were ambiguous and only 3 % single-copy orthologues retained gene order in three-way genome comparisons of the three genomes. Lots of NBS-encoding genes present in the either ancestor could not be found in the bread wheat. These results indicated that NBS-LRR genes in bread wheat might have evolved rapidly through a rapid loss of ancestor genes.

Widely distributed hot and cold spots in meiotic recombination as shown by the sequencing of rice F2 plants.

Numerous studies have argued that environmental variations may contribute to evolution through the generation of novel heritable variations via meiotic recombination, which plays a crucial role in crop domestication and improvement. Rice is one of the most important staple crops, but no direct estimate of recombination events has yet been made at a fine scale. Here, we address this limitation by sequencing 41 rice individuals with high sequencing coverage and c. 900 000 accurate markers. An average of 33.9 crossover (c. 4.53 cM Mb(-1) ) and 2.47 non-crossover events were detected per F2 plant, which is similar to the values in Arabidopsis. Although not all samples in the stress treatment group showed an increased number of crossover events, environmental stress increased the recombination rate in c. 28.5% of samples. Interestingly, the crossovers showed a highly uneven distribution among and along chromosomes, with c. 13.9% of the entire genome devoid of crossovers, including 11 of the 12 centromere regions, and c. 0.72% of the genome containing large numbers of crossovers (> 50 cM Mb(-1) ). The gene ontology (GO) categories showed that genes clustered within the recombination hot spot regions primarily tended to be involved in responses to environmental stimuli, suggesting that recombination plays an important role for adaptive evolution in rapidly changing environments.

Rapid evolution of avirulence genes in rice blast fungus Magnaporthe oryzae.

BACKGROUND: Rice blast fungus Magnaporthe oryzae is one of the most devastating pathogens in rice. Avirulence genes in this fungus share a gene-for-gene relationship with the resistance genes in its host rice. Although numerous studies have shown that rice blast R-genes are extremely diverse and evolve rapidly in their host populations, little is known about the evolutionary patterns of the Avr-genes in the pathogens. RESULTS: Here, six well-characterized Avr-genes and seven randomly selected non-Avr control genes were used to investigate the genetic variations in 62 rice blast strains from different parts of China. Frequent presence/absence polymorphisms, high levels of nucleotide variation (~10-fold higher than non-Avr genes), high non-synonymous to synonymous substitution ratios, and frequent shared non-synonymous substitution were observed in the Avr-genes of these diversified blast strains. In addition, most Avr-genes are closely associated with diverse repeated sequences, which may partially explain the frequent presence/absence polymorphisms in Avr-genes. CONCLUSION: The frequent deletion and gain of Avr-genes and rapid non-synonymous variations might be the primary mechanisms underlying rapid adaptive evolution of pathogens toward virulence to their host plants, and these features can be used as the indicators for identifying additional Avr-genes. The high number of nucleotide polymorphisms among Avr-gene alleles could also be used to distinguish genetic groups among different strains.

Transcriptomic and weighted gene co-expression network analysis of tropic and temperate maize inbred lines recovering from heat stress.

Heat stress (HS) causes imbalance of cellular homeostasis, growth impairment and extensively yield loss in crop production. In the present study, the tropic maize inbred CIMBL55 showed more thermotolerance than the maize temperate inbred B73, with less leaf damage rate and ROS accumulation. Transcriptome profiling of CIMBL55 and B73 upon (exposing at 45 â„ƒ for 0, 1, and 6 h) and post (recovering at 28 â„ƒ for 1 and 6 h) HS were further assessed and a total of 20204 DEGs were identified. Functional annotation revealed that HS activated unfolded protein response in endoplasmic reticulum in both two inbreds. Moreover, in CIMBL55, far more primary and secondary metabolism pathways were transcriptional altered. Afterwards, weighted gene co-expression analysis grouped all expressed genes into eighteen co-expressed modules. Four HS responsive and four CIMBL55 recovery-related modules were subsequently identified. Highly connected genes (hub genes) in these modules were characterized as transcription factors, heat shock proteins, Ca2+ signaling related genes and various enzymes. Moreover, one hub gene, ZmHsftf13 was verified to positively regulate thermotolerance by heterologous expressing in Arabidopsis and its Mu insertion mutant. The present research provides promising genes related to HS response in maize and is of great significance for breeding.

Whole-Genome Duplication and Purifying Selection Contributes to the Functional Redundancy of Auxin Response Factor (ARF) Genes in Foxtail Millet (Setaria italica L.).

Auxin response factors (ARFs) play crucial roles in auxin-mediated response, whereas molecular genetics of ARF genes was seldom investigated in Setaria italica, an important crop and C4 model plant. In the present study, genome-wide evolutionary analysis of ARFs was performed in S. italica. Twenty-four SiARF genes were identified and unevenly distributed on eight of the nine chromosomes in S. italica. Duplication mode exploration implied that 13 SiARF proteins were originated from whole-genome duplication and suffered purifying selection. Phylogeny reconstruction of SiARFs by maximum likelihood and neighbor-joining trees revealed SiARFs could be divided into four clades. SiARFs clustered within the same clade shared similar gene structure and protein domain composition, implying functional redundancy. Moreover, amino acid composition of the middle regions was conserved in SiARFs belonged to the same clade. SiARFs were categorized into either activators or repressors according to the enrichment of specific amino acids. Intrinsic disorder was featured in the middle regions of ARF activators. Finally, expression profiles of SiARFs under hormone and abiotic stress treatment not only revealed their potential function in stress response but also indicate their functional redundancy. Overall, our results provide insights into evolutionary aspects of SiARFs and benefit for further functional characterization.

ZmmiR190 and its target regulate plant responses to drought stress through an ABA-dependent pathway.

MicroRNAs (miRNAs) are small, non-coding regulatory RNAs that regulate gene expression by facilitating target mRNA cleavage in plants. They are crucial for responses to diverse stresses. The novel drought-responsive miRNA ZmmiR190 was previously identified during an analysis of the maize transcriptome. In this study, we revealed that transgenic Arabidopsis thaliana overexpressing ZmmiR190 is more sensitive to drought than the wild-type control. The transcript of a nuclear-localized gene, ZmCRP04, was identified as a likely target of ZmmiR190. Moreover, ZmmiR190 and ZmCRP04 had the opposite expression profiles following drought and salt treatments. Additionally, 5' RACE and coexpression analyses in A. thaliana provided evidence of the in vivo targeting of the ZmCRP04 transcript by ZmmiR190. Furthermore, the overexpression of ZmCRP04 in A. thaliana and rice significantly enhanced drought tolerance, with lower malonaldehyde contents and relative electrolyte leakage in the transgenic A. thaliana and rice plants than in the wild-type control. Transgenic plants overexpressing ZmmiR190 or ZmCRP04 were hypersensitive to abscisic acid. These results suggest that the ZmCRP04 transcript is targeted by ZmmiR190 and may encode a protein that positively regulates drought stress tolerance via an abscisic acid-dependent pathway. These findings may be relevant for future molecular breeding aimed at improving crop drought tolerance.

Ectopic Overexpression of Maize Heat Stress Transcription Factor ZmHsf05 Confers Drought Tolerance in Transgenic Rice.

Drought is a key factor affecting plant growth and development. Heat shock transcription factors (Hsfs) have been reported to respond to diverse abiotic stresses, including drought stress. In the present study, functional characterization of maize heat shock transcription factor 05 (ZmHsf05) gene was conducted. Homologous analysis showed that ZmHsf05 belongs to Class A2 Hsfs. The mRNA expression level of ZmHsf05 can be affected by drought, high temperature, salt, and abscisic acid (ABA) treatment. Ectopic overexpression of ZmHsf05 in rice (Oryza sativa) could significantly enhance the drought tolerance. Faced with drought stress, transgenic rice exhibited better phenotypic performance, higher survival rate, higher proline content, and lower leaf water loss rate, compared with wild-type plant Zhonghua11. Additionally, we assessed the agronomic traits of seven transgenic rice lines overexpressing ZmHsf05 and found that ZmHsf05 altered agronomical traits in the field trials. Moreover, rice overexpressing ZmHsf05 was more sensitive to ABA and had either a lower germination rate or shorter shoot length under ABA treatment. The transcription level of key genes in the ABA synthesis and drought-related pathway were significantly improved in transgenic rice after drought stress. Collectively, our results showed that ZmHsf05 could improve drought tolerance in rice, likely in an ABA-dependent manner.

Maize factors ZmUBP15, ZmUBP16 and ZmUBP19 play important roles for plants to tolerance the cadmium stress and salt stress.

Ubiquitin-Specific Protease16 (UBP16) has been described involved in cadmium stress and salt stress in Arabidopsis, however nothing is known about the functions of its homologs in maize. In this study, we investigate the functions of ZmUBP15, ZmUBP16 and ZmUBP19, three Arabidopsis UBP16 homologs in maize. Our results indicate that ZmUBP15, ZmUBP16 and ZmUBP19 are ubiquitously expressed throughout plant development, and ZmUBP15, ZmUBP16 and ZmUBP19 proteins are mainly localized in plasma membrane. Complementation analyses show that over-expression of ZmUBP15 or ZmUBP16 can rescue the defective phenotype of ubp16-1 in cadmium stress. In addition, over-expression of ZmUBP15, ZmUBP16 or ZmUBP19 can increase the plant tolerance to cadmium stress. These results indicate that ZmUBP15, ZmUBP16 and ZmUBP19 are required for plant to tolerance the cadmium stress. Consistent with this point, cadmium-related genes are markedly up-regulated in seedlings over-expressing ZmUBP15, ZmUBP16 or ZmUBP19. Furthermore, our data indicate that ZmUBP15, ZmUBP16 and ZmUBP19 partially rescue the salt-stress phenotype of ubp16-1. Thus, our research uncover the functions of three novel maize proteins, ZmUBP15, ZmUBP16 and ZmUBP19, which are required for plants in response to cadmium stress and salt stress.

Genome-Wide Investigation and Expression Profiling of HD-Zip Transcription Factors in Foxtail Millet (Setaria italica L.).

HD-Zip proteins represent the major transcription factors in higher plants, playing essential roles in plant development and stress responses. Foxtail millet is a crop to investigate the systems biology of millet and biofuel grasses and the HD-Zip gene family has not been studied in foxtail millet. For further investigation of the expression profile of the HD-Zip gene family in foxtail millet, a comprehensive genome-wide expression analysis was conducted in this study. We found 47 protein-encoding genes in foxtail millet using BLAST search tools; the putative proteins were classified into four subfamilies, namely, subfamilies I, II, III, and IV. Gene structure and motif analysis indicate that the genes in one subfamily were conserved. Promotor analysis showed that HD-Zip gene was involved in abiotic stress. Duplication analysis revealed that 8 (~17%) hdz genes were tandemly duplicated and 28 (58%) were segmentally duplicated; purifying duplication plays important roles in gene expansion. Microsynteny analysis revealed the maximum relationship in foxtail millet-sorghum and foxtail millet-rice. Expression profiling upon the abiotic stresses of drought and high salinity and the biotic stress of ABA revealed that some genes regulated responses to drought and salinity stresses via an ABA-dependent process, especially sihdz29 and sihdz45. Our study provides new insight into evolutionary and functional analyses of HD-Zip genes involved in environmental stress responses in foxtail millet.