The procambium specification gene Oshox1 promotes polar auxin transport capacity and reduces its sensitivity toward inhibition

A novel OsHB5-OsAPL-OsMADS27/OsWRKY102 regulatory module regulates grain size in rice

Grain size, a crucial trait that determines rice yield and quality, is typically regulated by multiple genes. Although numerous genes controlling grain size have been identified, the precise and dynamic regulatory network governing grain size is still not fully understood. In this study, we unveiled a novel regulatory module composed of OsHB5, OsAPL and OsMADS27/OsWRKY102, which plays a crucial role in modulating grain size in rice. As a positive regulator of grain size, OsAPL has been found to interact with OsHB5 both in vitro and in vivo. Through chromatin immunoprecipitation-sequencing, we successfully mapped two potential targets of OsAPL, namely OsMADS27, a positive regulator in grain size and OsWRKY102, a negative regulator in lignification that is also associated with grain size control. Further evidence from EMSA and chromatin immunoprecipitation-quantitative PCR experiments has shown that OsAPL acts as an upstream transcription factor that directly binds to the promoters of OsMADS27 and OsWRKY102. Moreover, EMSA and dual-luciferase reporter assays have indicated that the interaction between OsAPL and OsHB5 enhances the repressive effect of OsAPL on OsMADS27 and OsWRKY102. Collectively, our findings discovered a novel regulatory module, OsHB5-OsAPL-OsMADS27/OsWRKY102, which plays a significant role in controlling grain size in rice. These discoveries provide potential targets for breeding high-yield and high-quality rice varieties.

Developmental regulation of leaf venation patterns: monocot versus eudicots and the role of auxin

Organisation and patterning of the vascular network in land plants varies in different taxonomic, developmental and environmental contexts. In leaves, the degree of vascular strand connectivity influences both light and CO₂ harvesting capabilities as well as hydraulic capacity. As such, developmental mechanisms that regulate leaf venation patterning have a direct impact on physiological performance. Development of the leaf venation network requires the specification of procambial cells within the ground meristem of the primordium and subsequent proliferation and differentiation of the procambial lineage to form vascular strands. An understanding of how diverse venation patterns are manifest therefore requires mechanistic insight into how procambium is dynamically specified in a growing leaf. A role for auxin in this process was identified many years ago, but questions remain. In this review we first provide an overview of the diverse venation patterns that exist in land plants, providing an evolutionary perspective. We then focus on the developmental regulation of leaf venation patterns in angiosperms, comparing patterning in eudicots and monocots, and the role of auxin in each case. Although common themes emerge, we conclude that the developmental mechanisms elucidated in eudicots are unlikely to fully explain how parallel venation patterns in monocot leaves are elaborated.

The role of HD-Zip class I transcription factors in plant response to abiotic stresses

Abiotic stresses usually affect plant growth and development, indirectly or directly causing crop production reduction and even plant death. To survive, plants utilize different mechanisms to adapt themselves to continuously changing surrounding environmental stresses. Homeodomain-leucine zipper (HD-Zip) transcription factors are unique to the plant kingdom and divided into four different subfamilies (HD-Zip I∼IV). Many HD-Zip I members have been shown to play critical roles in the regulation of plant developmental processes, signaling networks and responses to environmental stresses. This review focuses on the role of HD-Zip I transcription factors in plant responses to various abiotic stresses, including abscisic acid-mediated stress, drought and cold stress, oxidative stress, helping to identify the potential regulatory mechanisms that alleviate abiotic stress in plants.

Small Grain and Dwarf 2, encoding an HD-Zip II family transcription factor, regulates plant development by modulating gibberellin biosynthesis in rice

Homeodomain leucine zipper (HD-Zip) proteins are transcription factors that regulate plant development. Bioactive gibberellin (GA) is a key endogenous hormone that participates in plant growth. However, the relationship between HD-Zip genes and modulation of GA biosynthesis in rice remains elusive. Here, we identified a rice mutant, designated as small grain and dwarf 2 (sgd2), which had reduced height and grain size compared with the wild type. Cytological observations indicated that the defective phenotype was mainly due to decreased cell length. Map-based cloning and complementation tests demonstrated that a 9 bp deletion in a homeodomain leucine zipper (HD-Zip) II family transcription factor was responsible for the sgd2 mutant phenotype. Expression of SGD2 was pronounced in developing panicles, and its protein was localized in nucleus. Luciferase reporter system and transactivation assays in yeast suggested that SGD2 functioned as a transcriptional repressor. High performance liquid chromatography assays showed that the endogenous GA₁ level in the sgd2 mutant was dramatically decreased, and exogenous GA₃ recovered the second leaf sheath to normal length. Results of qRT-PCR showed that the expression levels of genes positively regulating GA-biosynthesis were mostly down-regulated in the mutant. Our data identified the role of an HD-Zip transcription factor that affects rice plant development by modulating gibberellin biosynthesis.

Understanding the Genetic Basis of C4 Kranz Anatomy with a View to Engineering C3 Crops

One of the most remarkable examples of convergent evolution is the transition from C₃ to C₄ photosynthesis, an event that occurred on over 60 independent occasions. The evolution of C₄ is particularly noteworthy because of the complexity of the developmental and metabolic changes that took place. In most cases, compartmentalized metabolic reactions were facilitated by the development of a distinct leaf anatomy known as Kranz. C₄ Kranz anatomy differs from ancestral C₃ anatomy with respect to vein spacing patterns across the leaf, cell-type specification around veins, and cell-specific organelle function. Here we review our current understanding of how Kranz anatomy evolved and how it develops, with a focus on studies that are dissecting the underlying genetic mechanisms. This research field has gained prominence in recent years because understanding the genetic regulation of Kranz may enable the C₃-to-C₄ transition to be engineered, an endeavor that would significantly enhance crop productivity.

Molecular cloning and characterization of a brassinosteriod biosynthesis-related gene PtoDWF4 from Populus tomentosa

Brassinosteroids (BRs) as steroid hormones play an important role in plant growth and development. However, little is known about how BRs affect secondary wall biosynthesis in woody plants. In this study, we cloned and characterized PtoDWF4, a homologus gene of Arabidopsis DWF4 encoding a cytochrome P450 protein, from Populus tomentosa. qRT-PCR analysis showed that PtoDWF4 was highly expressed in stems, especially in xylem. Overexpression of PtoDWF4 (PtoDWF4-OE) in poplar promoted growth rate and biomass yield, increased area and cell layers of xylem. Transgenic plants showed a significant increase in plant height and stem diameter compared with the wild type. In contrast, the CRISPR/Cas9-generated mutation of PtoDWF4 (PtoDWF4-KO) resulted in significantly decreased biomass production in transgenic plants. Further studies revealed that constitutive expression of PtoDWF4 up-regulated the expression of secondary cell wall (SCW) biosynthesis-related genes, whereas knock-out of PtoDWF4 down-regulated their expression. Quantitative analysis of cell wall components showed a significant increase in PtoDWF4-OE lines but a reduction in PtoDWF4-KO lines compared with wild-type plants. Taken together, our results indicate that PtoDWF4 plays a positive role in improving growth rate and elevating biomass production in poplar.

Comprehensive characterization and RNA-Seq profiling of the HD-Zip transcription factor family in soybean (Glycine max) during dehydration and salt stress

BACKGROUND

The homeodomain leucine zipper (HD-Zip) transcription factor family is one of the largest plant specific superfamilies, and includes genes with roles in modulation of plant growth and response to environmental stresses. Many HD-Zip genes are characterized in Arabidopsis (Arabidopsis thaliana), and members of the family are being investigated for abiotic stress responses in rice (Oryza sativa), maize (Zea mays), poplar (Populus trichocarpa) and cucumber (Cucmis sativus). Findings in these species suggest HD-Zip genes as high priority candidates for crop improvement.

RESULTS

In this study we have identified members of the HD-Zip gene family in soybean cv. 'Williams 82', and characterized their expression under dehydration and salt stress. Homology searches with BLASTP and Hidden Markov Model guided sequence alignments identified 101 HD-Zip genes in the soybean genome. Phylogeny reconstruction coupled with domain and gene structure analyses using soybean, Arabidopsis, rice, grape (Vitis vinifera), and Medicago truncatula homologues enabled placement of these sequences into four previously described subfamilies. Of the 101 HD-Zip genes identified in soybean, 88 exist as whole-genome duplication-derived gene pairs, indicating high retention of these genes following polyploidy in Glycine ~13 Mya. The HD-Zip genes exhibit ubiquitous expression patterns across 24 conditions that include 17 tissues of soybean. An RNA-Seq experiment performed to study differential gene expression at 0, 1, 6 and 12 hr soybean roots under dehydration and salt stress identified 20 differentially expressed (DE) genes. Several of these DE genes are orthologs of genes previously reported to play a role under abiotic stress, implying conservation of HD-Zip gene functions across species. Screening of HD-Zip promoters identified transcription factor binding sites that are overrepresented in the DE genes under both dehydration and salt stress, providing further support for the role of HD-Zip genes in abiotic stress responses.

CONCLUSIONS

We provide a thorough description of soybean HD-Zip genes, and identify potential candidates with probable roles in dehydration and salt stress. Expression profiles generated for all soybean genes, under dehydration and salt stress, at four time points, will serve as an important resource for the soybean research community, and will aid in understanding plant responses to abiotic stress.

Grain number, plant height, and heading date7 is a central regulator of growth, development, and stress response

Grain number, plant height, and heading date7 (Ghd7) has been regarded as an important regulator of heading date and yield potential in rice (Oryza sativa). In this study, we investigated functions of Ghd7 in rice growth, development, and environmental response. As a long-day dependent negative regulator of heading date, the degree of phenotypic effect of Ghd7 on heading date and yield traits is quantitatively related to the transcript level and is also influenced by both environmental conditions and genetic backgrounds. Ghd7 regulates yield traits through modulating panicle branching independent of heading date. Ghd7 also regulates plasticity of tiller branching by mediating the PHYTOCHROME B-TEOSINTE BRANCHED1 pathway. Drought, abscisic acid, jasmonic acid, and high-temperature stress strongly repressed Ghd7 expression, whereas low temperature enhanced Ghd7 expression. Overexpression of Ghd7 increased drought sensitivity, whereas knock-down of Ghd7 enhanced drought tolerance. Gene chip analysis of expression profiles revealed that Ghd7 was involved in the regulation of multiple processes, including flowering time, hormone metabolism, and biotic and abiotic stresses. This study suggests that Ghd7 functions to integrate the dynamic environmental inputs with phase transition, architecture regulation, and stress response to maximize the reproductive success of the rice plant.

Genetic and hormonal regulation of cambial development

The stems and roots of most dicot plants increase in diameter by radial growth, due to the activity of secondary meristems. Two types of meristems function in secondary plant body formation: the vascular cambium, which gives rise to secondary xylem and phloem, and the cork cambium, which produces a bark layer that replaces the epidermis and protects the plant stem from mechanical damage and pathogens. Cambial development, the initiation and activity of the vascular cambium, leads to an accumulation of wood, the secondary xylem tissue. The thick, cellulose-rich cell walls of wood provide a source of cellulose and have the potential to be used as a raw material for sustainable and renewable energy production. In this review, we will discuss what is known about the mechanisms regulating the cambium and secondary tissue development.

The interaction of plant biotic and abiotic stresses: from genes to the field

Plant responses to different stresses are highly complex and involve changes at the transcriptome, cellular, and physiological levels. Recent evidence shows that plants respond to multiple stresses differently from how they do to individual stresses, activating a specific programme of gene expression relating to the exact environmental conditions encountered. Rather than being additive, the presence of an abiotic stress can have the effect of reducing or enhancing susceptibility to a biotic pest or pathogen, and vice versa. This interaction between biotic and abiotic stresses is orchestrated by hormone signalling pathways that may induce or antagonize one another, in particular that of abscisic acid. Specificity in multiple stress responses is further controlled by a range of molecular mechanisms that act together in a complex regulatory network. Transcription factors, kinase cascades, and reactive oxygen species are key components of this cross-talk, as are heat shock factors and small RNAs. This review aims to characterize the interaction between biotic and abiotic stress responses at a molecular level, focusing on regulatory mechanisms important to both pathways. Identifying master regulators that connect both biotic and abiotic stress response pathways is fundamental in providing opportunities for developing broad-spectrum stress-tolerant crop plants.

The physiological mechanism of a drooping leaf2 mutation in rice

Here we characterized a classic rice (Oryza sativa) drooping leaf2 mutant (named dl2). The dl2 allele affects both the midrib development and the total leaf venation pattern. Leaf anatomy results revealed the central vein lacks both clear cells and the adaxial small vascular bundle in dl2 mutant, which seemed to cause the drooping leaf phenotype. The dl2 leaves contain more small veins, and the size of the vascular cylinder in dl2 leaf is also altered. Furthermore, similar anatomy alteration was found in the dl2 roots. A reduction in the number of xylem and phloem poles in the central vascular cylinder in dl2 roots was observed and the diameter of cortical cell is also reduced. In addition, the alterations of the vegetative development such as the longer leaf blade and fewer adventitious and lateral roots were also observed in dl2. The physiological mechanism underlying the morphological and vascular alterations of dl2 was further studied. The result demonstrated that the dl2 vascular patterning distortions are strictly associated with a defective PAT (polar auxin transport) activity and sensitivity to different classes of polar auxin transport inhibitors. Finally, the drooping leaf phenotype of dl2 is coupled to a defective response to auxin.

Establishment and maintenance of vascular cell communities through local signaling

During plant development, cell fates are often determined by cell-to-cell communication. The vascular system, in which procambial/cambial cells continue to provide cells to two conductive tissues, xylem and phloem, is an excellent model for understanding cell-to-cell communication as a developmental cue. Recent studies on vascular development have revealed several novel intercellular signaling molecules that regulate vascular cell fates by unique mechanisms. This review focuses on emerging novel concepts such that reciprocal signaling by a transcription factor and microRNAs between the stele and the endodermis determines xylem cell patterns, and that a small peptide secreted from phloem governs vascular stem-cell maintenance.

Three cotton homeobox genes are preferentially expressed during early seedling development and in response to phytohormone signaling

Homeodomain-leucine zipper (HD-Zip) proteins are transcription factors unique to plants. In this study, three cDNAs (designated as GhHB2, GhHB3 and GhHB4) encoding HD-Zip proteins were isolated from cotton cDNA library. GhHB2 gene encodes a protein of 300 amino acids, GhHB3 gene encodes a peptide with 254 amino acids, and GhHB4 gene encodes a protein of 281 amino acids. The deduced proteins, which contain the homeodomain and leucine-rich zipper motif, share relatively high similarities with the other plant HD-Zip proteins. Quantitative RT-PCR analysis indicated that GhHB3 and GhHB4 were preferentially expressed in hypocotyls and cotyledons, whereas GhHB2 gene was predominantly expressed in young stems, at relatively high levels in hypocotyls. Expressions of all the three genes were up-regulated in roots, hypocotyls and cotyledons after GA(3) treatments. Additionally, GhHB4 expression was enhanced by 6-BA treatment. A GhHB2 promoter fragment was isolated from cotton by Genome-Walking PCR. Expression of GUS gene controlled under GhHB2 promoter was examined in the transgenic Arabidopsis plants. Strong GUS staining was detected in cotyledon, veins of the emerging leaves and shoot apices of 5- to 15-day-old transgenic seedlings, but GUS activity became more and more weak as the seedlings further developed. In addition, the promoter activity was induced by exogenous GA, indicating that GhHB2 promoter is very active during early seedling development, and may be GA-inducible. The results suggested that the three HB genes may function in early seedling development of cotton and in response to gibberellin signaling.

COE1, an LRR-RLK responsible for commissural vein pattern formation in rice

Leaf veins have a complex network pattern. Formation of this vein pattern has been widely studied as a model of tissue pattern formation in plants. To understand the molecular mechanism governing the vascular patterning process, we isolated the rice mutant, commissural vein excessive1 (coe1). The coe1 mutants had short commissural vein (CV) intervals and produced clustered CVs. Application of 1-N-naphthylphthalamic acid and brefeldin A decreased CV intervals, and application of 1-naphthaleneacetic acid increased CV intervals in wild-type rice; however, coe1 mutants were insensitive to these chemicals. COE1 encodes a leucine-rich repeat receptor-like kinase, whose amino acid sequence is similar to that of brassinosteroid-insensitive 1-associated receptor kinase 1 (BAK1), and which is localized at the plasma membrane. Because of the sequence similarity of COE1 to BAK1, we also examined the involvement of brassinosteroids in CV formation. Brassinolide, an active brassinosteroid, decreased the CV intervals of wild-type rice, and brassinazole, an inhibitor of brassinosteroid biosynthesis, increased the CV intervals of wild-type rice, but coe1 mutants showed insensitivity to these chemicals. These results suggest that auxin and brassinosteroids regulate CV intervals in opposite directions, and COE1 may regulate CV intervals downstream of auxin and brassinosteroid signals.

Mutation of the rice Narrow leaf1 gene, which encodes a novel protein, affects vein patterning and polar auxin transport

The size and shape of the plant leaf is an important agronomic trait. To understand the molecular mechanism governing plant leaf shape, we characterized a classic rice (Oryza sativa) dwarf mutant named narrow leaf1 (nal1), which exhibits a characteristic phenotype of narrow leaves. In accordance with reduced leaf blade width, leaves of nal1 contain a decreased number of longitudinal veins. Anatomical investigations revealed that the culms of nal1 also show a defective vascular system, in which the number and distribution pattern of vascular bundles are altered. Map-based cloning and genetic complementation analyses demonstrated that Nal1 encodes a plant-specific protein with unknown biochemical function. We provide evidence showing that Nal1 is richly expressed in vascular tissues and that mutation of this gene leads to significantly reduced polar auxin transport capacity. These results indicate that Nal1 affects polar auxin transport as well as the vascular patterns of rice plants and plays an important role in the control of lateral leaf growth.

A genome-wide survey of HD-Zip genes in rice and analysis of drought-responsive family members

The homeodomain leucine zipper (HD-Zip) genes encode transcription factors that have diverse functions in plant development and have often been implicated in stress adaptation. The HD-Zip genes are the most abundant group of homeobox (HB) genes in plants and do not occur in other eukaryotes. This paper describes the complete annotation of the HD-Zip families I, II and III from rice and compares these gene families with Arabidopsis in a phylogeny reconstruction. Orthologous pairs of rice and Arabidopsis HD-Zip genes were predicted based on neighbour joining and maximum parsimony (MP) trees with support of conserved intron-exon organization. Additionally, a number of HD-Zip genes appeared to be unique to rice. Searching of EST and cDNA databases and expression analysis using RT-PCR showed that 30 out of 31 predicted rice HD-Zip genes are expressed. Most HD-Zip genes were broadly expressed in mature plants and seedlings, but others showed more organ specific patterns. Like in Arabidopsis and other dicots, a subset of the rice HD-Zip I and II genes was found to be regulated by drought stress. We identified both drought-induced and drought-repressed HD-Zip genes and demonstrate that these genes are differentially regulated in drought-sensitive versus drought-tolerant rice cultivars. The drought-repressed HD-Zip family I gene, Oshox4, was selected for promoter-GUS analysis, showing that drought-responsiveness of Oshox4 is controlled by the promoter and that Oshox4 expression is predominantly vascular-specific. Loss-of-function analysis of Oshox4 revealed no specific phenotype, but overexpression analysis suggested a role for Oshox4 in elongation and maturation processes.

Induction of xylem and fiber differentiation inPopulus tremuloidesThis article is one of a selection of papers published in the Special Issue on Poplar Research in Canada

Vascular tissues are of particular importance to terrestrial plants as they allow long-distance transport within the plant and also provide support for upright growth. Nowhere are these traits more obvious than in tree species. Here we have evaluated the role of auxin transport in the differentiation of primary and secondary vascular tissues in a tree species, trembling aspen ( Populus tremuloides Michx). We found that a partial inhibition of auxin transport resulted in increased width and numbers of veins in leaves. A similar vascular overgrowth was observed during early secondary vascular differentiation of stems. This stem overgrowth consisted almost entirely of early differentiation of metaxylem and fibers. We hypothesize that the early differentiation of metaxylem and fibers results from inhibitor-induced accumulation of auxin in stems and that the differentiation of these tissues requires higher levels of auxin exposure than protoxylem. The controlled conditions used in this study also provide a framework for reverse genetics approaches to identify genes involved in vascular differentiation based on elevated expression in tissues developing vascular overgrowth.

Over-expression of OsAGAP, an ARF-GAP, interferes with auxin influx, vesicle trafficking and root development

Development and organogenesis in both dicot and monocot plants are highly dependent on polar auxin transport (PAT), which requires the proper asymmetric localization of both auxin influx and efflux carriers. In the model dicot plant Arabidopsis thaliana, the trafficking and localization of auxin efflux facilitators such as PIN-FORMED1 (PIN1) are mediated by GNOM, a guanine-nucleotide exchange factor (GEF) for the ADP-ribosylation factor (ARF) family of small GTPases, but molecular regulators of the auxin influx facilitators remain unknown. Here, we show that over-expression of OsAGAP, an ARF-GTPase-activating protein (ARF-GAP) in rice, impaired PAT and interfered with both primary and lateral root development. The lateral root phenotype could be rescued by the membrane-permeable auxin 1-naphthyl acetic acid, but not by indole 3-acetic acid (IAA) or by 2,4-dichloro-phenoxyacetic acid, which require influx facilitators to enter the cells. OsAGAP-over-expressing plants had alterations in vesicle trafficking and localization of the presumptive A. thaliana auxin-influx carrier AUX1, but not in the localization of the auxin efflux facilitators. Together, our data suggest that OsAGAP has a specific role in regulating vesicle trafficking pathways such as the auxin influx pathway, which in turn controls auxin-dependent root growth in plants.

A homeodomain leucine zipper gene from Craterostigma plantagineum regulates abscisic acid responsive gene expression and physiological responses

A subset of homeodomain leucine zipper proteins (HDZip) play a role in regulating adaptation responses including developmental adjustment to environmental cues in plants. Here we report the structural and functional characterisation of a dehydration responsive nuclear-targeted HDZip transcriptional regulator, CpHB-7. DNA-protein interaction studies suggest that CDeT6-19, a known ABA and dehydration responsive dehydrin gene, is a potential target gene of CpHB-7 in the desiccation-tolerant plant Craterostigma plantagineum. Transgenic plants that ectopically express CpHB-7 display reduced sensitivity towards ABA during seed germination and stomatal closure. Expression analysis reveals that genes with induced or repressed expression in CpHB-7 ectopic expression lines are either mostly repressed or induced by ABA, drought or salt treatment respectively, thus demonstrating that CpHB-7 modifies ABA-responsive gene expression as a negative regulator. CpHB-7 gene expression is also linked to early organ development, leading to the suggestion that CpHB-7 is functionally similar to the Arabidopsis transcription factor, ATHB-6.

Multiple regulatory elements contribute to the vascular-specific expression of the rice HD-Zip gene Oshox1 in Arabidopsis

The primary vascular tissues of plants differentiate from a single precursor tissue, the procambium. The role of upstream regulatory sequences in the transcriptional control of early vascular-specific gene expression is largely unknown. The onset of expression of the rice homeodomain-leucine zipper (HD-Zip) gene Oshox1 marks procambial cells that have acquired their distinctive anatomical features but do not yet display any overt signs of terminal vascular differentiation. The expression pattern of Oshox1 in rice appears to be mainly controlled by the activity of the 1.6 kb upstream promoter region. Here, we show that the Oshox1 promoter directs vascular, auxin- and sucrose-responsive reporter gene expression in Arabidopsis plants in a fashion comparable with that in rice. This is the case not only during normal development but also upon experimental manipulation, suggesting that the cis-acting regulatory elements that are instrumental in Oshox1 expression pattern are conserved between rice and Arabidopsis. Finally, through analysis of reporter gene expression profiles conferred by progressive 5' deletions of the Oshox1 promoter in transgenic Arabidopsis, we have identified upstream regulatory regions required for auxin and sucrose inducibility, and for cell type-, tissue- and organ-specific aspects of Oshox1 expression. Our study suggests that Oshox1 embryonic vascular expression is mainly achieved through suppression of expression in non-vascular tissues.

Cloning and characterization of an HDZip I gene GmHZ1 from soybean

By using cDNA-AFLP, we analyzed a recombinant inbred line population of soybean that was derived from a soybean mosaic virus (SMV) resistant cultivar Kefeng No.1 and a susceptible cultivar Nannong 1138-2. One hundred and eight fragments showing polymorphism between SMV resistant and susceptible pools were identified. One fragment w27 was 96 bp in length and showed homology to homeobox ggth with a coding region of 738 bp, encoding a protein of 245 amino acids. The genomic sequence analysis defined an intron of 521 bp in the coding region. GmHZ1 was characterized by the presence of a homeodomain (HD) with a closely linked leucine zipper motif (Zip). Southern blot analysis indicated that there was a single copy of GmHZ1 in the soybean genome. When inoculated with SMV strain N3, resistant and susceptible varieties showed reduced and increased expression of the GmHZ1, respectively. The fusion protein of GmHZ1 with GFP was targeted only in nucleus. Yeast two hybrid studies revealed that the GmHZ1 had transcriptional activation activity and can form homodimer. GmHZ1 can bind two 9-bp pseudopalindromic elements (CAAT(A/T)ATTG and CAAT(C/G)ATTG) with different affinity. Using GUS as a reporter gene, GmHZ1 was proved to be a transcriptional activator and enhanced GUS expression by binding with the two elements in plant cells. These results indicate that the GmHZ1 may have a transcriptional activator function in plant response to SMV infection.

Pattern formation in the vascular system of monocot and dicot plant species

Plant vascular tissues are organised in continuous strands, the longitudinal and radial patterns of which are intimately linked to the signals that direct plant architecture as a whole. Therefore, understanding the mechanisms underlying vascular tissue patterning is expected to shed light on patterning events beyond those that organise the vascular system, and thus represents a central issue in plant developmental biology. A number of recent advances, reviewed here, are leading to a more precise definition of the signals that control the formation of vascular tissues and their integration into a larger organismal context. Contents Summary 209 I. Introduction 209 II. The plant vascular system 210 III. Ontogeny of the vascular tissues 210 IV. Procambium development 210 V. The organisation of the vascular tissues 212 VI. The regulation of longitudinal vascular pattern formation 214 VII. The regulation of radial vascular pattern formation 220 VIII. Genetic screens for vascular development mutants 231 IX. Genes involved in vascular development identified through reverse genetics approaches 235 X. Conclusions and perspectives 235 Note added at the revision stage 236 Acknowledgements 236 References 236.

Overexpression analysis of plant transcription factors

Transcription factors (TFs) play important roles in plant development and its response to the environment. A variety of reverse genetics tools have been developed to study TF function, the two most commonly used ones being knockout and overexpression. Because of the unique characteristics and modes of action of TFs, the overexpression strategy has been particularly effective in revealing TF function. Thus, a number of overexpression-based methodologies - constitutive expression, tissue-specific expression, chemically inducible expression and overexpression of modified TFs - have been developed and are used in the analysis of TF function.

The RADICLELESS1 gene is required for vascular pattern formation in rice

The molecular mechanisms through which the complex patterns of plant vascular tissues are established are largely unknown. The highly ordered, yet simple, striate array of veins of rice leaves represents an attractive system to study the dynamics underlying pattern formation. Here we show that mutation in the RADICLELESS1 (RAL1) gene results in distinctive vascular pattern defects. In ral1 embryonic scutella, secondary veins are absent and in the prematurely aborted and discontinuous primary veins, cells are misaligned to each other. In ral1 leaves, longitudinal and commissural (transverse) veins display altered spacing and the commissural veins additionally show atypical branching and interruptions in their continuity. The vascular pattern alterations of ral1 occur in the context of normally shaped leaf primordia. Anatomical inspection and analysis of the expression of the procambium specification marker Oshox1-GUS and of the auxin-inducible reporter DR5-GUS demonstrates that all the vascular patterning aberrations of ral1 originate from defects in the procambium, which represents the earliest identifiable stage of vascular development. Furthermore, the ral1 mutant is unique in that procambium formation in leaf primordium development is delayed. Finally, the ral1 vascular patterning distortions are associated with a defective response to auxin and with an enhanced sensitivity to cytokinin. ral1 is the first mutant impaired in both procambium development and vascular patterning to be isolated in a monocot species.