Over-expression of a flower-specific transcription factor gene AtMYB24 causes aberrant anther development

Cloning the promoter of the sucrose transporter gene PsSUT2 and screening its upstream transcription factors in tree peony

Sucrose is an essential energy substance for tree peony (Paeonia Suffruticosa) floral organ development. However, little is known about the sucrose regulatory network in tree peony. In this study, the promoter sequence of the tree peony sucrose transporter gene PsSUT2 was cloned. Through cis-acting elements analysis and weighted gene co-expression network analysis (WGCNA), 6 transcription factors potentially regulating PsSUT2 were screened. Expression analysis revealed that the 6 transcription factors had similar expression trends with the PsSUT2 in all parts of peony at the full bloom stage. Furthermore, a yeast one-hybrid assay revealed that PsMYB20 and PsMADS9 bind to the PsSUT2 promoter. Dual-luciferase reporter assay demonstrated that PsMYB20 and PsMADS9 could activate PsSUT2 expression. Taken together, our findings suggest that PsMYB20 and PsMADS9 positively regulate PsSUT2, laying the foundation for the construction of a gene network for sucrose regulation in tree peony.

Transcriptome profiling of foxtail millet (Setaria italica) pollen and anther

Pollen development and germination play a crucial role in the sexual reproduction of plants. This study analysis of transcriptional dynamics of foxtail millet pollen with other tissues and organs (ovule, glume, seedling and root) through RNA-sequencing revealed that a total of 940 genes were up-regulated in foxtail millet pollen. Based on this, we analyzed the genes involved in pollen tube growth of receptor kinases and small peptides, calcium signaling, small G proteins, vesicle transport, cytoskeleton, cell wall correlation, and transcription factors that are up-regulated in pollen. At the same time, we compared the gene expression of foxtail millet pollen and mature anthers, and found that a large number of transcription factors were specific expressed in mature anthers. In addition, we verified the accuracy of the transcriptome data using RT-qPCR. Finally, employed the antisense Oligonucleotide (as-ODN) system found that inhibiting SiPME67 expression would cause abnormal growth of pollen tube subapical. In summary, we preliminarily analyzed the genes that were up-regulated in foxtail millet pollen, which provided a reference for understanding the male sterility mechanism of foxtail millet in the future and theoretical basis for creating new male sterility lines.

MYB transcription factors in plants: A comprehensive review of their discovery, structure, classification, functional diversity and regulatory mechanism

The MYB transcription factor (TF) family is one of the largest families in plants and performs highly diverse regulatory functions, particularly in relation to pathogen/pest resistance, nutrient/noxious substance absorption, drought/salt resistance, trichome growth, stamen development, leaf senescence, and flavonoid/terpenoid biosynthesis. Owing to their vital role in various biological regulatory processes, the mechanisms of MYB TFs have been extensively studied. Notably, MYB TFs not only directly regulate targets, such as phytohormones, reactive oxygen species signaling and secondary cell wall formation, but also serve as crucial points of crosstalk between these signaling networks. Here, we have comprehensively described the structures, classifications, and biological functions of MYB TFs, with a specific focus on their roles and mechanisms in the response to biotic and abiotic stresses, plant morphogenesis, and secondary metabolite biosynthesis. Different from other reported reviews, this review provides comprehensive knowledge on plant MYB TFs and will provide valuable insights in understanding regulatory networks and associated functions of plant MYB TFs to apply in resistance breeding and crop improvement.

Pepper defense against Ralstonia solanacearum and High-temperature stress is positively regulated by CaMYB59

We have functionally evaluated a transcription factor CaMYB59 for its role in pepper immune responses to Ralstonia solanacearum attack and high temperature-high humidity (HTHH). Exposure to R. solanacearum inoculation (RSI) and HTHH resulted in up-regulation of this nucleus-localized TF. Function of this TF was confirmed by performing loss of function assay of CaMYB59 by VIGS (virus-induced gene silencing). Plants with silenced CaMYB59 displayed not only compromised pepper immunity against RSI but also impaired tolerance to HTHH along with decreased hypersensitive response (HR). This impairment in defense function was fully linked with low induction of stress-linked genes like CaPO2, CaPR1, CaAcc and thermo-tolerance linked CaHSP24 as well as CaHsfB2a. Conversely, transient overexpression of CaMYB59 enhanced pepper immunity. This reveals that CaMYB59 positively regulated host defense against RSI and HTHH by means of HR like mimic cell death, H2O2 production and up-regulation of defense as well as thermo-tolerance associated genes. These changes in attributes collectively confirm the role of CaMYB59 as a positive regulator of pepper immunity against R. solanacearum. We recommend that such positive regulation of pepper defense is dynamically supported by phyto-hormone signaling and transcriptional web of defense genes. These integrated and interlinked events stabilize plant growth and survival under abiotic and biotic stresses.

Genome-wide identification and characterization of the KCS gene family in sorghum (Sorghum bicolor (L.) Moench)

The aboveground parts of plants are covered with cuticle, a hydrophobic layer composed of cutin polyester and cuticular wax that can protect plants from various environmental stresses. β-Ketoacyl-CoA synthase (KCS) is the key rate-limiting enzyme in plant wax synthesis. Although the properties of KCS family genes have been investigated in many plant species, the understanding of this gene family in sorghum is still limited. Here, a total of 25 SbKCS genes were identified in the sorghum genome, which were named from SbKCS1 to SbKCS25. Evolutionary analysis among different species divided the KCS family into five subfamilies and the SbKCSs were more closely related to maize, implying a closer evolutionary relationship between sorghum and maize. All SbKCS genes were located on chromosomes 1, 2, 3, 4, 5, 6, 9 and 10, respectively, while Chr 1 and Chr 10 contained more KCS genes than other chromosomes. The prediction results of subcellular localization showed that SbKCSs were mainly expressed in the plasma membrane and mitochondria. Gene structure analysis revealed that there was 0-1 intron in the sorghum KCS family and SbKCSs within the same subgroup were similar. Multiple cis-acting elements related to abiotic stress, light and hormone response were enriched in the promoters of SbKCS genes, which indicated the functional diversity among these genes. The three-dimensional structure analysis showed that a compact spherical space structure was formed by various secondary bonds to maintain the stability of SbKCS proteins, which was necessary for their biological activity. qRT-PCR results revealed that nine randomly selected SbKCS genes expressed differently under drought and salt treatments, among which SbKCS8 showed the greatest fold of expression difference at 12 h after drought and salt stresses, which suggested that the SbKCS genes played a potential role in abiotic stress responses. Taken together, these results provided an insight into investigating the functions of KCS family in sorghum and in response to abiotic stress.

Comparative transcriptomic analysis of maize ear heterosis during the inflorescence meristem differentiation stage

BACKGROUND

Heterosis is widely used in many crops and is important for global food safety, and maize is one of the most successful crops to take advantage of heterosis. Gene expression patterns control the development of the maize ear, but the mechanisms by which heterosis affects transcriptional-level control are not fully understood.

RESULTS

In this study, we sampled ear inflorescence meristems (IMs) from the single-segment substitution maize (Zea mays) line lx9801^hlEW2b, which contains the heterotic locus hlEW2b associated with ear width, as well as the receptor parent lx9801, the test parent Zheng58, and their corresponding hybrids Zheng58 × lx9801^hlEW2b (HY) and Zheng58 × lx9801 (CK). After RNA sequencing and transcriptomic analysis, 2531 unique differentially expressed genes (DEGs) were identified between the two hybrids (HY vs. CK). Our results showed that approximately 64% and 48% of DEGs exhibited additive expression in HY and CK, whereas the other genes displayed a non-additive expression pattern. The DEGs were significantly enriched in GO functional categories of multiple metabolic processes, plant organ morphogenesis, and hormone regulation. These essential processes are potentially associated with heterosis performance during the maize ear developmental stage. In particular, 125 and 100 DEGs from hybrids with allele-specific expression (ASE) were specifically identified in HY and CK, respectively. Comparison between the two hybrids suggested that ASE genes were involved in different development-related processes that may lead to the hybrid vigor phenotype during maize ear development. In addition, several critical genes involved in auxin metabolism and IM development were differentially expressed between the hybrids and showed various expression patterns (additive, non-additive, and ASE). Changes in the expression levels of these genes may lead to differences in auxin homeostasis in the IM, affecting the transcription of core genes such as WUS that control IM development.

CONCLUSIONS

Our research suggests that additive, non-additive, and allele-specific expression patterns may fine-tune the expression of crucial DEGs that modulate carbohydrate and protein metabolic processes, nitrogen assimilation, and auxin metabolism to optimal levels, and these transcriptional changes may play important roles in maize ear heterosis. The results provide new information that increases our understanding of the relationship between transcriptional variation and heterosis during maize ear development, which may be helpful for clarifying the genetic and molecular mechanisms of heterosis.

Comprehensive analysis of the MYB transcription factor gene family in Morus alba

BACKGROUND

The V-myb myeloblastosis viral oncogene homolog (MYB) family of proteins is large, containing functionally diverse transcription factors. However, MYBs in Morus are still poorly annotated and a comprehensive functional analysis of these transcription factors is lacking.

RESULTS

In the present study, a genome-wide identification of MYBs in Morus alba was performed. In total 166 MaMYBs were identified, including 103 R2R3-MYBs and four 3R-MaMYBs. Comprehensive analyses, including the phylogenetic analysis with putative functional annotation, motif and structure analysis, gene structure organization, promoter analysis, chromosomal localization, and syntenic relationships of R2R3-MaMYBs and 3R-MaMYBs, provided primary characterization for these MaMYBs. R2R3-MaMYBs covered the subgroups reported for R2R3-MYBs in Arabidopsis and Populus, and had two Morus-specific subgroups, indicating the high retention of MYBs in Morus. Motif analysis revealed high conservative residues at the start and end of each helix and residues consisting of the third helix in R2 and R3 repeats. Thirteen intron/exon patterns (a-m) were summarized, and the intron/exon pattern of two introns with phase numbers of 0 and 2 was the prevalent pattern for R2R3-MaMYBs. Various cis-elements in promoter regions were identified, and were mainly related to light response, development, phytohormone response, and abiotic and biotic stress response and secondary metabolite production. Expression patterns of R2R3-MaMYBs in different organs showed that MaMYBs involved in secondary cell wall components and stress responsiveness were preferentially expressed in roots or stems. R2R3-MaMYBs involved in flavonoid biosynthesis and anthocyanin accumulation were identified and characterized based on functional annotation and correlation of their expression levels with anthocyanin contents.

CONCLUSION

Based on a comprehensive analysis, this work provided functional annotation for R2R3-MYBs and an informative reference for further functional dissection of MYBs in Morus.

The R2R3 MYB Transcription Factor MYB71 Regulates Abscisic Acid Response in Arabidopsis

Abscisic acid (ABA) regulates plant responses to abiotic stresses via regulating the expression of downstream genes, yet the functions of many ABA responsive genes remain unknown. We report here the characterization of MYB71, a R2R3 MYB transcription factor in regulating ABA responses in Arabidopsis. RT-PCR results show that the expression level of MYB71 was increased in response to ABA treatment. Arabidopsis protoplasts transfection results show that MYB71 was specifically localized in nucleus and it activated the Gal4:GUS reporter gene when recruited to the Gal4 promoter by a fused DNA binding domain GD. Roles of MYB71 in regulating plant response to ABA were analyzed by generating Arabidopsis transgenic plants overexpression MYB71 and gene edited mutants of MYB71. The results show that ABA sensitivity was increased in the transgenic plants overexpression MYB71, but decreased in the MYB71 mutants. By using a DEX inducible system, we further identified genes are likely regulated by MYB71, and found that they are enriched in biological process to environmental stimuli including abiotic stresses, suggesting that MYB71 may regulate plant response to abiotic stresses. Taken together, our results suggest that MYB71 is an ABA responsive gene, and MYB71 functions as a transcription activator and it positively regulates ABA response in Arabidopsis.

Overexpression of sesame polyketide synthase A leads to abnormal pollen development in Arabidopsis

BACKGROUND

Sesame is a great reservoir of bioactive constituents and unique antioxidant components. It is widely used for its nutritional and medicinal value. The expanding demand for sesame seeds is putting pressure on sesame breeders to develop high-yielding varieties. A hybrid breeding strategy based on male sterility is one of the most effective ways to increase the crop yield. To date, little is known about the genes and mechanism underlying sesame male fertility. Therefore, studies are being conducted to identify and functionally characterize key candidate genes involved in sesame pollen development. Polyketide synthases (PKSs) are critical enzymes involved in the biosynthesis of sporopollenin, the primary component of pollen exine. Their in planta functions are being investigated for applications in crop breeding.

RESULTS

In this study, we cloned the sesame POLYKETIDE SYNTHASE A (SiPKSA) and examined its function in male sterility. SiPKSA was specifically expressed in sesame flower buds, and its expression was significantly higher in sterile sesame anthers than in fertile anthers during the tetrad and microspore development stages. Furthermore, overexpression of SiPKSA in Arabidopsis caused male sterility in transgenic plants. Ultrastructural observation showed that the pollen grains of SiPKSA-overexpressing plants contained few cytoplasmic inclusions and exhibited an abnormal pollen wall structure, with a thicker exine layer compared to the wild type. In agreement with this, the expression of a set of sporopollenin biosynthesis-related genes and the contents of their fatty acids and phenolics were significantly altered in anthers of SiPKSA-overexpressing plants compared with wild type during anther development.

CONCLUSION

These findings highlighted that overexpression of SiPKSA in Arabidopsis might cause male sterility through defective pollen wall formation. Moreover, they suggested that SiPKSA modulates vibrant pollen development via sporopollenin biosynthesis, and a defect in its regulation may induce male sterility. Therefore, genetic manipulation of SiPKSA might promote hybrid breeding in sesame and other crop species.

Ethylene-induced NbMYB4L is involved in resistance against tobacco mosaic virus in Nicotiana benthamiana

Several MYB transcription factors are known to play important roles in plant resistance to environmental stressors. However, the mechanism governing the involvement of MYBs in regulating tobacco mosaic virus (TMV) resistance in plants is still unclear. In this study, we found that not only is Nicotiana benthamiana MYB4-like involved in defence against TMV, but also that the ethylene pathway participates in MYB4L-mediated resistance. Transcription of NbMYB4L was up-regulated in N. benthamiana infected with TMV. Silencing of NbMYB4L led to intensified TMV replication, whereas overexpression of NbMYB4L induced significant resistance to TMV. Transcription of NbMYB4L was greater in 1-aminocyclopropanecarboxylic acid (ACC, ethylene precursor)-pretreated plants but lower when the ethylene signalling pathway was blocked during TMV infection. Gene expression analysis showed that the transcription of NbMYB4L was largely suppressed in ETHYLENE INSENSITIVE 3-like 1(EIL1)-silenced plants. The results of electrophoretic mobility shift assay and chromatin immunoprecipitation-quantitative PCR (ChIP-qPCR) experiments indicated that NbEIL1 could directly bind to two specific regions of the NbMYB4L promoter. Furthermore, a luciferase assay revealed that NbEIL1 significantly induced the reporter activity of the MYB4L promoter in N. benthamiana. These results point to NbEIL1 functioning as a positive regulator of NbMYB4L transcription in N. benthamiana against TMV. Collectively, our work reveals that EIL1 and MYB4L constitute a coherent feed-forward loop involved in the robust regulation of resistance to TMV in N. benthamiana.

Sesame β-ketoacyl-acyl carrier protein synthase I regulates pollen development by interacting with an adenosine triphosphate-binding cassette transporter in transgenic Arabidopsis

Male gametogenesis is an important biological process critical for seed formation and successful breeding. Understanding the molecular mechanisms of male fertility might facilitate hybrid breeding and increase crop yields. Sesame anther development is largely unknown. Here, a sesame β-ketoacyl-[acyl carrier protein] synthase I (SiKASI) was cloned and characterized as being involved in pollen and pollen wall development. Immunohistochemical analysis showed that the spatiotemporal expression of SiKASI protein was altered in sterile sesame anthers compared with fertile anthers. In addition, SiKASI overexpression in Arabidopsis caused male sterility. Cytological observations revealed defective microspore and pollen wall development in SiKASI-overexpressing plants. Aberrant lipid droplets were detected in the tapetal cells of SiKASI-overexpressing plants, and most of the microspores of transgenic plants contained few cytoplasmic inclusions, with irregular pollen wall components embedded on their surfaces. Moreover, the fatty acid metabolism and the expression of a sporopollenin biosynthesis-related gene set were altered in the anthers of SiKASI-overexpressing plants. Additionally, SiKASI interacted with an adenosine triphosphate (ATP)-binding cassette (ABC) transporter. Taken together, our findings suggested that SiKASI was crucial for fatty acid metabolism and might interact with ABCG18 for normal pollen fertility in Arabidopsis.

Crocus transcription factors CstMYB1 and CstMYB1R2 modulate apocarotenoid metabolism by regulating carotenogenic genes

Two MYB genes have been identified which regulate apocarotenoid metabolism in Crocus sativus. Apocarotenoids like crocin, picrocrocin and safranal are restricted to genus Crocus and are synthesized by oxidative cleavage of zeaxanthin followed by glycosylation reactions. In Crocus sativus, these apocarotenoids are synthesized in stigma part of the flower in developmentally regulated manner. Most of the genes of apocarotenoid pathway are known, however, the mechanism that regulates its tissue and stage specific biosynthesis remains elusive. MYB family was identified as the largest transcription factor family from Crocus transciptome which indicated its possible role in apocarotenoid regulation besides regulating other metabolic pathways. Towards this, we started with identification of 150 MYB genes from Crocus transcriptome databases. The phylogenetic analysis of Crocus MYB genes divided them into 27 clusters. Domain analysis resulted in identification of four groups of MYBs depending upon the number of R repeats present. Expression profiling indicated that 12 MYBs are upregulated in stigma out of which expression of four genes CstMYB1, CstMYB14, CstMYB16 and CstMYB1R2 correlated with crocin accumulation. Transient overexpression of two nuclear localized MYB genes (CstMYB1 and CstMYB1R2) in Crocus confirmed their role in regulating carotenoid metabolism. Yeast-one-hybrid confirmed that CstMYB1 binds to carotenoid cleavage dioxygenase 2 (CCD2) promoter while CstMYB1R2 binds to phytoene synthase (PSY) and CCD2 promoters. Overall, our study established that CstMYB1 and CstMYB1R2 regulate apocarotenoid biosynthesis by directly binding to promoters of pathway genes.

Molecular mechanisms of mesocotyl elongation induced by brassinosteroid in maize under deep-seeding stress by RNA-sequencing, microstructure observation, and physiological metabolism

Deep-seeding is an important way to improve maize drought resistance, mesocotyl elongation can significantly enhance its seedling germination. To improve our understanding of transcription-mediated maize mesocotyl elongation under deep-seeding stress. RNA-sequencing was used to identify differentially expressed genes (DEGs) in both deep-seeding tolerant W64A and intolerant K12 mesocotyls following culture for 10 days after 2.0 mg·L^-1 24-epibrassinolide (EBR) induced stress at the depths of 3 and 20 cm. Phenotypically, the mesocotyl length of both maize significantly increased under 20 cm stress and in the presence of EBR. Microstructure observations revealed that the mesocotyls underwent programmed cell death under deep-seeding stress, which was alleviated by EBR. This was found to be regulated by multiple DEGs encoding cysteine protease/senescence-specific cysteine protease, aspartic protease family protein, phospholipase D, etc. and transcription factors (TFs; MYB, NAC). Additionally, some DEGs associated with cell wall components, i.e., cellulose synthase/cellulose synthase like protein (CESA/CSL), fasciclin-like arabinogalactan (APG), leucine-rich repeat protein (LRR) and lignin biosynthesis enzymes including phenylalanine ammonia-lyase, S-adenosyl-L-methionine-dependent methyltransferases, 4-coumarate-CoA ligase, cinnamoyl CoA reductase, cinnamyl alcohol dehydrogenase, catalase, peroxiredoxin/peroxidase were found to control cell wall sclerosis. Moreover, in auxin, ethylene, brassinosteriod, cytokinin, zeatin, abscisic acid, gibberellin, jasmonic acid, and salicylic acid signaling transduction pathways, the corresponding DEGs were activated/inhibited by TFs (ARF, BZR1/2, B-ARR, A-ARR, MYC2, ABF, TGA) and synthesis of phytohormones-related metabolites. These findings provide information on the molecular mechanisms controlling maize deep-seeding tolerance and will aid in the breeding of deep-seeding maize varieties.

Integrated Methylome and Transcriptome Analyses Reveal the Molecular Mechanism by Which DNA Methylation Regulates Kenaf Flowering

DNA methylation regulates key biological processes in plants. In this study, kenaf seedlings were pretreated with the DNA methylation inhibitor 5-azacytidine (5-azaC) (at concentrations of 0, 100, 200, 400, and 600 μM), and the results showed that pretreatment with 200 μM 5-azaC promoted flowering most effectively. To elucidate the underlying mechanism, phytohormone, adenosine triphosphate (ATP), and starch contents were determined, and genome-wide DNA methylation and transcriptome analyses were performed on anthers pretreated with 200 μM 5-azaC (5-azaC200) or with no 5-azaC (control conditions; 5-azaC0). Biochemical analysis revealed that 5-azaC pretreatment significantly reduced indoleacetic acid (IAA) and gibberellic acid (GA) contents and significantly increased abscisic acid (ABA) and ATP contents. The starch contents significantly increased in response to 200 and 600 μM 5-azaC. Further genome-wide DNA methylation analysis revealed 451 differentially methylated genes (DMGs) with 209 up- and 242 downregulated genes. Transcriptome analysis showed 3,986 differentially expressed genes (DEGs), with 2,171 up- and 1,815 downregulated genes. Integrated genome-wide DNA methylation and transcriptome analyses revealed 72 genes that were both differentially methylated and differentially expressed. These genes, which included ARFs, PP2C, starch synthase, FLC, PIF1, AGL80, and WRKY32, are involved mainly in plant hormone signal transduction, starch and sucrose metabolism, and flowering regulation and may be involved in early flowering. This study serves as a reference and theoretical basis for kenaf production and provides insights into the effects of DNA methylation on plant growth and development.

Genome-Wide Identification and Expression Analysis of MYB Transcription Factors and Their Responses to Abiotic Stresses in Woodland Strawberry (Fragaria vesca)

Woodland strawberry (Fragaria vesca) is a diploid strawberry that is widely used as a model of cultivated octoploid strawberry (Fragaria × ananassa). It has also been used as a model for Rosaceae fruits, non-climacteric fruits, and stolons. The MYB superfamily is the largest transcription factor family in plants, and its members play important roles in plant growth and development. However, the complete MYB superfamily in woodland strawberry has not been studied. In this study, a total of 217 MYB genes were identified in woodland strawberry and classified into four groups: one 4R-MYB protein, five 3R-MYB proteins, 113 2R-MYB proteins, and 98 1R-MYB proteins. The phylogenetic relationship of each MYB subgroup was consistent in terms of intron/exon structure and conserved motif composition. The MYB genes in woodland strawberry underwent loss and expansion events during evolution. The transcriptome data revealed that most FveMYB genes are expressed in several organs, whereas 15 FveMYB genes exhibit organ-specific expression, including five genes (FveMYB101, -112, -44, and -8; FveMYB1R81) in roots, two genes (FveMYB62 and -77) in stolon tips, three genes (FveMYB99 and -35; FveMYB1R96) in open flowers, and five genes (FveMYB76 and -100; FveMYB1R4, -5, and -86) in immature fruits. During fruit ripening of woodland strawberry, the expression levels of 84 FveMYB genes were decreased, of which five genes (FveMYB4, -22, -50, and -66; FveMYB1R57) decreased more than 10-fold, whereas those 18 FveMYB genes were increased, especially FveMYB10 and FveMYB74 increased more than 30-fold. In addition, the expression levels of 36, 68, 52, and 62 FveMYB genes were altered by gibberellic acid, abscisic acid, cold, and heat treatments, respectively, and among them, several genes exhibited similar expression patterns for multiple treatments, suggesting possible roles in the crosstalk of multiple signaling pathways. This study provides candidate genes for the study of stolon formation, fruit development and ripening, and abiotic stress responses.

Auxin and Flower Development: A Blossoming Field

The establishment of the species-specific floral organ body plan involves many coordinated spatiotemporal processes, which include the perception of positional information that specifies floral meristem and floral organ founder cells, coordinated organ outgrowth coupled with the generation and maintenance of inter-organ and inter-whorl boundaries, and the termination of meristem activity. Auxin is integrated within the gene regulatory networks that control these processes and plays instructive roles at the level of tissue-specific biosynthesis and polar transport to generate local maxima, perception, and signaling. Key features of auxin function in several floral contexts include cell nonautonomy, interaction with cytokinin gradients, and the central role of MONOPTEROS and ETTIN to regulate canonical and noncanonical auxin response pathways, respectively. Arabidopsis flowers are not representative of the enormous angiosperm floral diversity; therefore, comparative studies are required to understand how auxin underlies these developmental differences. It will be of great interest to compare the conservation of auxin pathways among flowering plants and to discuss the evolutionary role of auxin in floral development.

Genome-wide identification and expression analysis of the MYB transcription factor in Japanese plum (Prunus salicina)

MYB proteins constitute one of the largest transcription factor families in plants, members of which are involved in various plant physiological and biochemical processes. Japanese plum (Prunus salicina) is one of the important stone fruit crops worldwide. To date, no comprehensive study of the MYB family in Japanese plum has been reported. In this study, we performed genome-wide analysis of MYB genes in Japanese plum including the phylogeny, gene structures, protein motifs, chromosomal locations, collinearity and expression patterns analysis. A total of 96 Japanese plum R2R3-MYB (PsMYB) genes were characterized and distributed on 8 chromosomes at various densities. Collinearity analysis indicated that the segmental duplication events played a crucial role in the expansion of PsMYB genes, and the interspecies synteny analysis revealed the orthologous gene pairs between Japanese plum and other four selected Rosaceae species. The 96 PsMYB genes could be classified into 27 subgroups based on phylogenetic topology, as supported by the conserved gene structures and motif compositions. Further comparative phylogenetic analysis revealed the functional divergence of MYB gene family during evolution, and three subgroups which included only Rasaceae MYB genes were identified. Expression analysis revealed the distinct expression profiles of the PsMYB genes, and further functional predictions found some of them might be associated with the plum fruit quality traits. Our researches provide a global insight into the organization, phylogeny, evolution and expression patterns of the PsMYB genes, and contribute to the greater understanding of their functional roles in Japanese plum.

Two responses to MeJA induction of R2R3-MYB transcription factors regulate flavonoid accumulation in Glycyrrhiza uralensis Fisch

Flavonoids are key components of licorice plant that directly affect its medicinal quality. Importantly, the MYB family of transcription factors serves to regulate the synthesis of flavonoids in plants. The MYB transcription factors represent one of the largest families of transcription factors in plants and play important roles in the process of plant growth and development. MYB gene expression is induced by a number of plant hormones, including the lipid-based hormone jasmonate (JA). Methyl jasmonate (MeJA) is an endogenous plant growth regulator that can induce the JA signaling pathway, which functions to regulate the synthesis of secondary metabolites, including flavonoids. In this study, MeJA was added to licorice cell suspensions, and RNA-seq analysis was performed to identify the differentially expressed genes. As a result, the MYB transcription factors GlMYB4 and GlMYB88 were demonstrated to respond significantly to MeJA induction. Subsequently, the GlMYB4 and GlMYB88 protein were shown to localize to the cell nucleus, and it was verified that GlMYB4 and GlMYB88 could positively regulate the synthesis of flavonoids in licorice cells. Overall, this research helps illustrate the molecular regulation of licorice flavonoid biosynthesis induced by MeJA.

Analysis of differentially expressed genes and pathways associated with male sterility lines in watermelon via bulked segregant RNA-seq

Genic male sterility (GMS) is a common and important trait, which is widely used for the production of hybrid seeds. However, the molecular mechanism of GMS in watermelon remains poorly understood. In this study, we comparatively analyzed the transcriptome profiles of sterile and fertile floral buds using the bulked segregant analysis (BSA) and transcriptome sequencing (RNA-seq). A total of 2507 differentially expressed genes (DEGs) including 593 up-regulated and 1914 down-regulated, were identified to be related to male sterility in watermelon line Se18. Gene ontology (GO) analysis showed that 57 GO terms were significantly enriched, while Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis revealed plant hormone signal transduction, glycolysis/gluconeogenesis, starch and sucrose metabolism, plant-pathogen interaction, phenylpropanoid biosynthesis pathways were obviously enriched. Furthermore, the efficiency of the RNA-seq analysis was validated by quantitative real-time PCR (qRT-PCR). Among the DEGs, some valuable candidate genes involved in pollen development were identified, such as gene Cla000029, a bHLH transcription factor and homologous to MS1 in Arabidopsis. Moreover, other DEGs including MYB gene Cla012590 (MYB26), Cla017100 (MYB21), etc., also provide useful information for further understanding the function of key genes involved in pollen development. This study provides new insights into the global network of male sterility in watermelon.

Narrowing Down a Major QTL Region Conferring Pod Fiber Contents in Yardlong Bean (Vigna unguiculata), a Vegetable Cowpea

Yardlong bean (Vigna unguiculata (L.) Walp. ssp. sesquipedalis), a subgroup of cowpea, is an important vegetable legume crop of Asia where its young pods are consumed in both fresh and cooked forms. Pod fiber contents (cellulose, hemicellulose and lignin) correlates with pod tenderness (softness/hardness) and pod shattering. In a previous study using populations derived from crosses between yardlong bean and wild cowpea (V. unguiculata ssp. unguiculata var. spontanea), three major quantitative trait loci (QTLs), qCel7.1, qHem7.1 and qLig7.1, controlling these fibers were identified on linkage group 7 (cowpea chromosome 5) and are co-located with QTLs for pod tenderness and pod shattering. The objective of this study was to identify candidate gene(s) controlling the pod fiber contents. Fine mapping for qCel7.1, qHem7.1 and qLig7.1 was conducted using F₂ and F_2:3 populations of 309 and 334 individuals, respectively, from the same cross combination. New DNA markers were developed from cowpea reference genome sequence and used for fine mapping. A QTL analysis showed that in most cases, each pod fiber content was controlled by one major and one minor QTLs on the LG7. The major QTLs for cellulose, hemicellulose and lignin in pod were always mapped to the same regions or close to each other. In addition, a major QTL for pod shattering was also located in the region. Although there were several annotated genes relating to pod fiber contents in the region, two genes including Vigun05g266600 (VuBGLU12) encoding a beta glucosidase and Vigun05g273500 (VuMYB26b) encoding a transcription factor MYB26 were identified as candidate genes for the pod fiber contents and pod shattering. Function(s) of these genes in relation to pod wall fiber biosynthesis and pod shattering was discussed.

SmCOI1 affects anther dehiscence in a male-sterile Solanum melongena line

Anther indehiscence is an important form of functional male sterility that can facilitate the production of hybrid seed; however, the molecular mechanisms of anther indehiscence-based male sterility have not been thoroughly explored in eggplant (Solanum melongena L.). Here, we used two-dimensional gel electrophoresis to compare the protein profiles in the anthers of normally developing (F142) and anther indehiscent (S16) S. melongena plants. Four differentially expressed proteins were identified using matrix-assisted laser desorption/ionization time-of-flight/time-of-flight mass spectrometry. Of these proteins, the transcript accumulation of the eggplant CORONATINE INSENSITIVE1 (SmCOI1) was significantly downregulated in S16 relative to F142. Phylogenetic analysis showed that SmCOI1 has high amino acid sequence similarity and clustered into the same subgroup as its homologs in other members of the Solanaceae. Subcellular localization analysis showed that SmCOI1 localized to the nucleus. Moreover, reverse-transcription quantitative PCR revealed that the jasmonic acid pathway genes SmJAZ1 and SmOPR3 are upregulated in F142 relative to S16. Protein-protein interaction studies identified a direct interaction between SmCOI1 and SmOPR3, but SmCOI1 failed to interact with SmJAZ1. These findings shed light on the regulatory mechanisms of anther dehiscence in eggplant.

Jasmonate Signaling during Arabidopsis Stamen Maturation

The last stages of stamen development, collectively called stamen maturation, encompass pollen viability, filament elongation and anther dehiscence or opening. These processes are essential for male fertility in Arabidopsis and require the function of jasmonate signaling. There is a good understanding of jasmonate synthesis, perception and transcriptional outputs in Arabidopsis stamens. In addition, the spatiotemporal localization of jasmonate signaling components at the tissue and cellular levels has started to emerge in recent years. However, the ultimate cellular functions activated by jasmonate to promote stamen maturation remain unknown. The hormones auxin and gibberellin have been proposed to control the activation of jasmonate synthesis to promote stamen maturation, although we hypothesize that this action is rather indirect. In this review, we examine these different areas, attempt to clarify some confusing aspects found in the literature and raise testable hypothesis that may help to further understand how jasmonate controls male fertility in Arabidopsis.

Effects on Plant Growth and Reproduction of a Peach R2R3-MYB Transcription Factor Overexpressed in Tobacco

In plants, anthocyanin production is controlled by MYB and bHLH transcription factors. In peach, among the members of these families, MYB10.1 and bHLH3 have been shown to be the most important genes for production of these pigments during fruit ripening. Anthocyanins are valuable molecules, and the overexpression of regulatory genes in annual fast-growing plants has been explored for their biotechnological production. The overexpression of peach MYB10.1 in tobacco plants induced anthocyanin pigmentation, which was particularly strong in the reproductive parts. Pigment production was the result of an up-regulation of the expression level of key genes of the flavonoid biosynthetic pathway, such as NtCHS, NtCHI, NtF3H, NtDFR, NtANS, and NtUFGT, as well as of the proanthocyanidin biosynthetic pathway such as NtLAR. Nevertheless, phenotypic alterations in transgenic tobacco lines were not only limited to anthocyanin production. Lines showing a strong phenotype (type I) exhibited irregular leaf shape and size and reduced plant height. Moreover, flowers had reduced length of anther's filament, nondehiscent anthers, reduced pistil length, aborted nectary glands, and impaired capsule development, but the reproductive parts including androecium, gynoecium, and petals were more pigmented that in wild type. Surprisingly, overexpression of peach MYB10.1 led to suppression of NtMYB305, which is required for floral development and, of one of its target genes, NECTARIN1 (NtNCE1), involved in the nectary gland formation. MYB10.1 overexpression up-regulated JA biosynthetic (NtAOS) and signaling (NtJAZd) genes, as well as 1-aminocyclopropane-1-carboxylate oxidase (NtACO) in flowers. The alteration of these hormonal pathways might be among the causes of the observed floral abnormalities with defects in both male and female gametophyte development. In particular, approximately only 30% of pollen grains of type I lines were viable, while during megaspore formation, there was a block during FG1 (St3-II). This block seemed to be associated to an excessive accumulation of callose. It can be concluded that the overexpression of peach MYB10.1 in tobacco not only regulates flavonoid biosynthesis (anthocyanin and proanthocyanidin) in the reproductive parts but also plays a role in other processes such as vegetative and reproductive development.

Overexpression of a stamen-specific R2R3-MYB gene BcMF28 causes aberrant stamen development in transgenic Arabidopsis

In flowering plants, stamen development is a complex multistage process, which is highly regulated by a series of transcription factors. In this study, BcMF28, which encodes a R2R3-MYB transcription factor, was isolated from Brassica campestris. BcMF28 is localized in the nucleus and cytoplasm, and acts as a transcriptional activator. Quantitative real-time PCR and promoter activity analysis revealed that BcMF28 was predominately expressed in inflorescences. The expression of BcMF28 was specifically detected in tapetum, developing microspores, anther endothecium, and filaments during late stamen development. The overexpression of BcMF28 in Arabidopsis resulted in aberrant stamen development, including filament shortening, anther indehiscence, and pollen abortion. Detailed analysis of anther development in transgenic plants revealed that the degeneration of septum and stomium did not occur, and endothecium lignification was affected. Furthermore, the expression levels of genes involved in the phenylpropanoid metabolism pathway were altered in BcMF28-overexpressing transgenic plants. Our results suggest that BcMF28 plays an important regulatory role during late stamen development.

Research advances of MYB transcription factors in plant stress resistance and breeding

Plants face various stresses during the growth and development processes. The specific transcription factors bind to the cis-acting elements upstream of the stress resistance genes, specifically regulating the expression of the gene in plants and increasing the adaptability of plants to environmental stress. The transcription factor-mediated gene expression regulatory networks play an important role in plant stress response pathways. MYB (v-myb avian myeloblastosis viral oncogene homolog) transcription factor is one of the largest members of the transcription factor family in plants. It participates and has a great influence on all aspects of plant growth and development. It plays an important role in plant secondary metabolic regulation, hormone and environmental factor responses, cell differentiation, organ morphogenesis, and cell cycle regulation. This review mainly introduces the characteristics, structure, and classification of MYB transcription factors, as well as the abiotic stress resistance to drought, salt, temperature, and other functions in breeding, and provides a reference for the research and utilization of transcription factors in the future.

Transcriptional regulation of anther development in Arabidopsis

This review focuses on the current knowledge of transcription factors involved in Arabidopsis anther development. Anther development is a multistage process and controlled by a complex network of transcription factors acting in spatio/temporal manner. Molecular understanding of anther developmental pathway is critical from the perspective of controlling male fertility and hybrid generation. Generation of hybrid lines relies upon the effective mechanisms of controlling the process of pollen development and pollen release. Controlling any developmental program requires a good knowledge of regulatory pathways governing that developmental program. In a regulatory pathway, transcription factors represent an important link between the developmental program and response of genes to growth regulators and environmental signals. Therefore, identifying the entire cohort of anther specific transcription factors is an essential step towards the molecular understanding of regulatory networks involved in pollen formation and pollen release.

INDUCER OF CBF EXPRESSION 1 is a male fertility regulator impacting anther dehydration in Arabidopsis

INDUCER OF CBF EXPRESSION 1 (ICE1) encodes a MYC-like basic helix-loop-helix (bHLH) transcription factor playing a critical role in plant responses to chilling and freezing stresses and leaf stomata development. However, no information connecting ICE1 and reproductive development has been reported. In this study, we show that ICE1 controls plant male fertility via impacting anther dehydration. The loss-of-function mutation in ICE1 gene in Arabidopsis caused anther indehiscence and decreased pollen viability as well as germination rate. Further analysis revealed that the anthers in the mutant of ICE1 (ice1-2) had the structure of stomium, though the epidermis did not shrink to dehisce. The anther indehiscence and influenced pollen viability as well as germination in ice1-2 were due to abnormal anther dehydration, for most of anthers dehisced with drought treatment and pollen grains from those dehydrated anthers had similar viability and germination rates compared with wild type. Accordingly, the sterility of ice1-2 could be rescued by ambient dehydration treatments. Likewise, the stomatal differentiation of ice1-2 anther epidermis was disrupted in a different manner compared with that in leaves. ICE1 specifically bound to MYC-recognition elements in the promoter of FAMA, a key regulator of guard cell differentiation, to activate FAMA expression. Transcriptome profiling in the anther tissues further exhibited ICE1-modulated genes associated with water transport and ion exchange in the anther. Together, this work reveals the key role of ICE1 in male fertility control and establishes a regulatory network mediated by ICE1 for stomata development and water movement in the anther.

Promoters of Arabidopsis Casein kinase I-like 2 and 7 confer specific high-temperature response in anther

KEY MESSAGE: (1) We systematically analyze the promoter activities of AtCKLs in various tissues; (2) AtCKL2 and AtCKL7 were expressed in early developmental anthers under high temperature (HT) conditions; (3) AtMYB24 may function as a positive regulator of AtCKL2 and AtCKL7 expression under HT. High temperature (HT) can seriously impede plant growth and development, causing severe loss of crop production. In Arabidopsis, AtCKL genes show high similarity to GhCKI, a gene reported to disrupt tapetal programmed cell death in cotton. However, most of AtCKL genes are not well characterized. Here, we systematically analyzed the expression patterns of AtCKLs in various tissues. The expression of AtCKL2 and AtCKL7 was induced in early anther development under HT, which is similar to the case of GhCKI. In silico analysis of AtCKL2 and AtCKL7 promoters indicated that four types of transcription factors (TFs) (MADS, NAC, WRKY and R2R3-MYB) might bind to AtCKL2 and AtCKL7 promoters. Furthermore, three MADS, three NAC, one WRKY, and three R2R3-MYB TFs were up-regulated in stage 1-8 anthers and three R2R3-MYB TFs were up-regulated in stage 9-10 anthers under HT, implying the important roles of R2R3-MYB genes in the response of anthers to HT. Among the R2R3-MYB genes, AtMYB24 showed the similar expression as AtCKL2 and AtCKL7 in the anthers under HT. Additionally, yeast one-hybrid and dual-luciferase reporter system assays verified that AtMYB24 could bind to AtCKL2 and AtCKL7 promoters and activate the expression of these two genes. In brief, this study provides the overall expression profiles of AtCKLs, useful information for unraveling the molecular mechanism of AtCKL2 and AtCKL7 gene expression in early anther development under HT, and important clues for elucidating the mechanism of transcriptional regulation of CKI genes in plant anther under HT, which are critical to the reduction of crop yield loss resulting from HT.

The R2R3MYB Gene Family in Phyllostachys edulis: Genome-Wide Analysis and Identification of Stress or Development-Related R2R3MYBs

The MYB transcription factor (TF) is one of the largest gene families in plants and involved to multiple biological processes. However, little is known about the MYB family and its functional role in the genome of moso bamboo. In the present study, a total of 114 R2R3MYB genes were first identified from moso bamboo genome and full-length non-chimeric (FLNC) reads. Phylogenetic analysis coupled with gene structure analysis and motif determination resulted in the division of these PheR2R3MYBs into 17 subgroups. The position of eight proteins along an external branch in the phylogenetic tree suggested their relatively ancient origin. The genes in this group were all substituted by (Met, M)/(Arg, R) at conservative W residues in both R2 and R3 repeats, and half were found to possess no transcriptional activation activity. The analysis of evolutionary patterns and divergence suggests that the expansion of PheMYBs was mainly attributable to whole genome duplication (WGD) under different selection pressures. Expressional analysis based on microarray and qRT-PCR data performed diverse expression patterns of R2R3MYBs in response to both various abiotic stimuli and flower development. Furthermore, the co-expression analysis of R2R3MYBs suggested an intricate interplay of growth- and stress-related responses. Finally, we found a hub gene, PheMYB4, was involved in a complex proteins interaction network. Further functional analysis indicated that ectopic overexpression of its homologous gene, PheMYB4-1, could increase tolerance to cold treatment and sensitivity to drought and salt treatment of transgenic Arabidopsis seedlings. These findings provide comprehensive insights into the MYB family members in moso bamboo and offer candidate MYB genes for further studies on their roles in stress resistance.

GmMYB181, a Soybean R2R3-MYB Protein, Increases Branch Number in Transgenic Arabidopsis

Soybean (Glycine max) is an important economic crop that provides abundant oil and high quality protein for human beings. As the process of reproductive growth directly determines the crop seed yield and quality, we initiated studies to identify genes that regulate soybean floral organ development. One R2R3-MYB transcription factor gene, designated as GmMYB181, was found to be enriched in flowers based on microarray analysis and was further functionally investigated in transgenic Arabidopsis. GmMYB181 protein contains two MYB domains, which localized to the nucleus and displayed transcriptional activation in yeast hybrid system. Real-time quantitative PCR (qRT-PCR) results suggested GmMYB181 exclusively expressed in flower tissue. In Arabidopsis, overexpression of GmMYB181 altered the morphology of floral organs, fruit size and plant architecture, including outward curly sepals, smaller siliques, increased lateral branches and reduced plant height, indicating that GmMYB181 is involved in the development of reproductive organs and plays an important role in controlling plant architecture. Further, microarray analysis revealed that overexpressing GmMYB181 in Arabidopsis affected the expression of 3450 genes in mature flowers, including those involved in floral organ, seed/fruit development, and responded to different hormone signals.

Arabidopsis MYB24 Regulates Jasmonate-Mediated Stamen Development

The phytohormone jasmonates (JAs) regulate various defense responses and diverse developmental processes including stamen development and fertility. Previous studies showed that JA induces CORONATINE INSENSITIVE 1-mediated degradation of JA ZIM-domain (JAZ) proteins, and activates the MYB transcription factors (such as MYB21 and MYB24) to regulate stamen development. In this study, we further uncover the mechanism underlying how MYB24 interacts with JAZs to control JA-regulated stamen development. We show that N-terminus of MYB21/24 interacts with 10 out of 12 JAZ proteins while both N-terminus and C-terminus of MYB24 are involved in dimerization of MYB21 and MYB24. Interestingly, male sterility of the JA-deficient mutant opr3 can be rescued by suitable level of the MYB24 overexpression but not by excessive high level of MYB24. Surprisingly, overexpression of MYB24NT, but not MYB24CT, could cause male sterility. These results provide new insights on MYB factors in JA-regulated stamen development.

The VviMYB80 Gene is Abnormally Expressed in Vitis vinifera L. cv. 'Zhong Shan Hong' and its Expression in Tobacco Driven by the 35S Promoter Causes Male Sterility

Anther development is a very precise and complicated process. In Arabidopsis, the AtMYB80 transcription factor regulates genes involved in pollen development and controls the timing of tapetal programmed cell death (PCD). In this study, we isolated and characterized cDNA for VviMYB80 expressed in flower buds of male-sterile Vitis vinifera L. cv. 'Zhong Shan Hong', a late-maturing cultivar derived from self-progeny of cv. 'Wink'. VviMYB80 belongs to the MYB80 subfamily and clusters with AtMYB35/TDF1 in a distinct clade. We found that in flower buds, expression of the VviMYB80 gene in cv. 'Zhong Shan Hong' sharply increased at the tetrad stage, resulting in a higher and earlier transcript level than that found in cv. 'Wink'. Expression of the VviMYB80 gene, driven by the 35S promoter, caused pleiotropic effects on the stamens, including smaller and shriveled anthers, delayed dehiscence, fewer seeds, shorter anther filaments, distorted pollen shape and a lack of cytoplasm, with the tapetum exhibiting hypertrophy in transformed tobacco. These results suggest that VviMYB80 may play an important role in stamen development and that expression of VviMYB80 driven by the 35S promoter in tobacco induces male sterility.

Identification and expression analysis of genes related to calyx persistence in Korla fragrant pear

BACKGROUND

The objective of this study was to increase understanding about genetic mechanisms affecting calyx persistence in Korla fragrant pear (Pyrus brestschneideri Rehd). Flowers were collected at early bloom, full bloom, and late bloom. The RNA was extracted from the flowers and then combined according to calyx type. Transcriptome and digital gene expression (DGE) profiles of flowers, ovaries, and sepals with persistent calyx (SC_hua, SC_ep, and SC_zf, respectively) were compared with those of flowers, ovaries, and sepals with deciduous calyx (TL_hua, TL_ep, and TL_zf, respectively). Temporal changes in the expression of selected genes in floral organs with either persistent or deciduous calyx were compared using real-time quantitative PCR (qRT-PCR).

RESULTS

Comparison of the transcriptome sequences for SC_hua and TL_hua indicated 26 differentially expressed genes (DEGs) with known relationship to abscission and 10 DEGs with unknown function. We identified 98 MYB and 21 SPL genes from the assembled unigenes. From SC_zf vs TL_zf, we identified 21 DEGs with known relationship to abscission and 18 DEGs with unknown function. From SC_ep vs TL_ep, 12 DEGs with known relationship to abscission were identified along with 11 DEGs with unknown function. Ten DEGs were identified by both transcriptome sequencing and DGE sequencing.

CONCLUSIONS

More than 50 DEGs were observed that were related to calyx persistence in Korla fragrant pear. Some of the genes were related to cell wall degradation, plant hormone signal transduction, and stress response. Other DEGs were identified as zinc finger protein genes and lipid transfer protein genes. Further analysis showed that calyx persistence in Korla fragment pear was a metabolic process regulated by many genes related to cell wall degradation and plant hormones.

Regulation of Jasmonate-Mediated Stamen Development and Seed Production by a bHLH-MYB Complex in Arabidopsis

Stamens are the plant male reproductive organs essential for plant fertility. Proper development of stamens is modulated by environmental cues and endogenous hormone signals. Deficiencies in biosynthesis or perception of the phytohormone jasmonate (JA) attenuate stamen development, disrupt male fertility, and abolish seed production in Arabidopsis thaliana. This study revealed that JA-mediated stamen development and seed production are regulated by a bHLH-MYB complex. The IIIe basic helix-loop-helix (bHLH) transcription factor MYC5 acts as a target of JAZ repressors to function redundantly with other IIIe bHLH factors such as MYC2, MYC3, and MYC4 in the regulation of stamen development and seed production. The myc2 myc3 myc4 myc5 quadruple mutant exhibits obvious defects in stamen development and significant reduction in seed production. Moreover, these IIIe bHLH factors interact with the MYB transcription factors MYB21 and MYB24 to form a bHLH-MYB transcription complex and cooperatively regulate stamen development. We speculate that the JAZ proteins repress the bHLH-MYB complex to suppress stamen development and seed production, while JA induces JAZ degradation and releases the bHLH-MYB complex to subsequently activate the expression of downstream genes essential for stamen development and seed production.

TaLHY, a 1R-MYB Transcription Factor, Plays an Important Role in Disease Resistance against Stripe Rust Fungus and Ear Heading in Wheat

LHY (late elongated hypocotyl) is an important gene that regulates and controls biological rhythms in plants. Additionally, LHY is highly expressed in the SSH (suppression subtractive hybridization) cDNA library-induced stripe rust pathogen (CYR32) in our previous research. To identify the function of the LHY gene in disease resistance against stripe rust, we used RACE-PCR technology to clone TaLHY in the wheat variety Chuannong19. The cDNA of TaLHY is 3085 bp long with an open reading frame of 1947 bp. TaLHY is speculated to encode a 70.3 kDa protein of 648 amino acids , which has one typical plant MYB-DNA binding domain; additionally, phylogenetic tree shows that TaLHY has the highest homology with LHY of Brachypodium distachyon(BdLHY-like). Quantitative fluorescence PCR indicates that TaLHY has higher expression in the leaf, ear and stem of wheat but lower expression in the root. Infestation of CYR32 can result in up-regulated expression of TaLHY, peaking at 72 h. Using VIGS (virus-induced gene silencing) technology to disease-resistant wheat in the fourth leaf stage, plants with silenced TaLHY cannot complete their heading stage. Through the compatible interaction with the stripe rust physiological race CYR32, Chuannong 19 loses its immune capability toward the stripe rust pathogen, indicating that TaLHY may regulate and participate in the heading of wheat, as well as the defense responses against stripe rust infection.

Regulation of stamen development by coordinated actions of jasmonate, auxin, and gibberellin in Arabidopsis

Proper stamen development is essential for plants to achieve their life cycles. Defects in stamen development will cause male sterility. A vast array of research efforts have been made to understand stamen developmental processes and regulatory mechanisms over the past decades. It is so far reported that phytohormones, including jasmonate, auxin, gibberellin, brassinosteroid, and cytokinin, play essential roles in regulation of stamen development. This review will briefly summarize the molecular basis for coordinated regulation of stamen development by jasmonate, auxin, and gibberellin in Arabidopsis.

A cotton gene encoding MYB-like transcription factor is specifically expressed in pollen and is involved in regulation of late anther/pollen development

In flowering plants, pollen development is a highly programmed process, in which a lot of genes are involved. In this study, a gene, designated as GhMYB24, encoding R2R3-MYB-like protein was isolated from cotton. GhMYB24 protein is localized in the cell nucleus and acts as a transcriptional activator. Northern blot analysis revealed that GhMYB24 transcripts were predominantly detected in anthers. It was further found that strong expression of GhMYB24 was mainly detected in pollen and was regulated during anther development by in situ hybridization. Overexpression of GhMYB24 in Arabidopsis caused flower malformation, shorter filaments, non-dehiscent anthers and fewer viable pollen grains. Further analysis revealed that the septum and stomium cells of anthers were not broken, and fewer fibrous bands were found in the endothecium cells in transgenic plants. A complementation test demonstrated that GhMYB24 was able to recover partially the male fertility of the myb21 myb24 double mutant. Expression levels of the genes involved in the phenylpropanoid biosynthetic pathway and reactive oxygen species homeostasis were altered in GhMYB24-overexpressing transgenic plants. Furthermore, the genes involved in jasmonate biosynthesis and its signaling pathway were up-regulated in the transgenic plants. Yeast two-hybrid assay indicated that GhMYB24 interacted with GhJAZ1/2 in cells. Taking the data together, our results suggest that GhMYB24 may play an important role in normal anther/pollen development.

Transcriptional profiling of rice early response to Magnaporthe oryzae identified OsWRKYs as important regulators in rice blast resistance

Rice blast disease is a major threat to rice production worldwide, but the mechanisms underlying rice resistance to the causal agent Magnaporthe oryzae remain elusive. Therefore, we carried out a transcriptome study on rice early defense response to M. oryzae. We found that the transcriptional profiles of rice compatible and incompatible interactions with M. oryzae were mostly similar, with genes regulated more prominently in the incompatible interactions. The functional analysis showed that the genes involved in signaling and secondary metabolism were extensively up-regulated. In particular, WRKY transcription factor genes were significantly enriched among the up-regulated genes. Overexpressing one of these WRKY genes, OsWRKY47, in transgenic rice plants conferred enhanced resistance against rice blast fungus. Our results revealed the sophisticated transcriptional reprogramming of signaling and metabolic pathways during rice early response to M. oryzae and demonstrated the critical roles of WRKY transcription factors in rice blast resistance.

Oryza sativa COI homologues restore jasmonate signal transduction in Arabidopsis coi1-1 mutants

CORONATINE INSENSITIVE 1 (COI1) encodes an E3 ubiquitin ligase complex component that interacts with JAZ proteins and targets them for degradation in response to JA signaling. The Arabidopsis genome has a single copy of COI1, but the Oryza sativa genome has three closely related COI homologs. To examine the functions of the three OsCOIs, we used yeast two-hybrid assays to examine their interactions with JAZ proteins and found that OsCOIs interacted with OsJAZs and with JAZs, in a coronatine dependent manner. We also tested whether OsCOI1a and OsCOI1b could complement Arabidopsis coi1-1 mutants and found that overexpression of either gene in the coi1-1 mutant resulted in restoration of JA signal transduction and production of seeds, indicating successful complementation. Although OsCOI2 interacted with a few OsJAZs, we were not able to successfully complement the coi1-1 mutant with OsCOI2. Molecular modeling revealed that the three OsCOIs adopt 3D structures similar to COI1. Structural differences resulting from amino acid variations, especially among amino acid residues involved in the interaction with coronatine and JAZ proteins, were tested by mutation analysis. When His-391 in OsCOI2 was substituted with Tyr-391, OsCOI2 interacted with a wider range of JAZ proteins, including OsJAZ1, 2, 5∼9 and 11, and complemented coi1-1 mutants at a higher frequency than the other OsCOIs and COI1. These results indicate that the three OsCOIs are orthologues of COI1 and play key roles in JA signaling.

The R2R3-MYB, bHLH, WD40, and related transcription factors in flavonoid biosynthesis

R2R3-MYB, bHLH, and WD40 proteins have been shown to control multiple enzymatic steps in the biosynthetic pathway responsible for the production of flavonoids, important secondary metabolites in Camellia sinensis. Few related transcription factor genes have been documented. The presence of R2R3-MYB, bHLH, and WD40 were statistically and bioinformatically analyzed on 127,094 C. sinensis transcriptome unigenes, resulting in identification of 73, 49, and 134 genes, respectively. C. sinensis phylogenetic trees were constructed for R2R3-MYB and bHLH proteins using previous Arabidopsis data and further divided into 27 subgroups (Sg) and 32 subfamilies. Motifs in some R2R3-MYB subgroups were redefined. Furthermore, Sg26 and Sg27 were expanded compared to Arabidopsis data, and bHLH proteins in C. sinensis were grouped into nine subfamilies. According to the functional annotation of Arabidopsis, flavonoid biosynthesis in C. sinensis was predicted to include R2R3-MYB genes in Sg4 (6), Sg5 (2), and Sg7 (1), as well as bHLH genes in subfamily 2 (2) and subfamily 24 (5). The wide evolutionary gap prevented phylogenetic analysis of WD40s; however, a single gene, CsWD40-1, was observed to share 80.4 % sequence homogeny with AtTTG1. Analysis of CsMYB4-1, CsMYB4-2, CsMYB4-3, CsMYB4-4, CsMYB5-1, and CsMYB5-2 revealed the interaction motif [DE]Lx2[RK]x3Lx6Lx3R, potentially contributing to the specificity of the bHLH partner in the stable MYB-bHLH complex. Full-length end-to-end polymerase chain reaction (PCR) and quantitative reverse transcriptase (qRT)-PCR were used to validate selected genes and generate relative expression ratio profiles in C. sinensis leaves by developmental stage and treatment conditions, including hormone and wound treatments. Potential target binding sites were predicted.

Comparative transcript profiling of a male sterile cybrid pummelo and its fertile type revealed altered gene expression related to flower development

Male sterile and seedless characters are highly desired for citrus cultivar improvement. In our breeding program, a male sterile cybrid pummelo, which could be considered as a variant of male fertile pummelo, was produced by protoplast fusion. Herein, ecotopic stamen primordia initiation and development were detected in this male sterile cybrid pummelo. Histological studies revealed that the cybrid showed reduced petal development in size and width, and retarded stamen primordia development. Additionally, disorganized cell proliferation was also detected in stamen-like structures (fused to petals and/or carpel). To gain new insight into the underlying mechanism, we compared, by RNA-Seq analysis, the nuclear gene expression profiles of floral buds of the cybrid with that of fertile pummelo. Gene expression profiles which identified a large number of differentially expressed genes (DEGs) between the two lines were captured at both petal primordia and stamen primordia distinguishable stages. For example, nuclear genes involved in nucleic acid binding and response to hormone synthesis and metabolism, genes required for floral bud identification and expressed in particular floral whorls. Furthermore, in accordance with flower morphology of the cybrid, expression of PISTILLATA (PI) was reduced in stamen-like structures, even though it was restricted to correct floral whorls. Down-regulated expression of APETALA3 (AP3) coincided with that of PI. These finding indicated that, due to their whorl specific effects in flower development, citrus class-B MADS-box genes likely constituted ‘perfect targets’ for CMS retrograde signaling, and that dysfunctional mitochondria seemed to cause male sterile phenotype in the cybrid pummelo.

A regulatory network for coordinated flower maturation

For self-pollinating plants to reproduce, male and female organ development must be coordinated as flowers mature. The Arabidopsis transcription factors AUXIN RESPONSE FACTOR 6 (ARF6) and ARF8 regulate this complex process by promoting petal expansion, stamen filament elongation, anther dehiscence, and gynoecium maturation, thereby ensuring that pollen released from the anthers is deposited on the stigma of a receptive gynoecium. ARF6 and ARF8 induce jasmonate production, which in turn triggers expression of MYB21 and MYB24, encoding R2R3 MYB transcription factors that promote petal and stamen growth. To understand the dynamics of this flower maturation regulatory network, we have characterized morphological, chemical, and global gene expression phenotypes of arf, myb, and jasmonate pathway mutant flowers. We found that MYB21 and MYB24 promoted not only petal and stamen development but also gynoecium growth. As well as regulating reproductive competence, both the ARF and MYB factors promoted nectary development or function and volatile sesquiterpene production, which may attract insect pollinators and/or repel pathogens. Mutants lacking jasmonate synthesis or response had decreased MYB21 expression and stamen and petal growth at the stage when flowers normally open, but had increased MYB21 expression in petals of older flowers, resulting in renewed and persistent petal expansion at later stages. Both auxin response and jasmonate synthesis promoted positive feedbacks that may ensure rapid petal and stamen growth as flowers open. MYB21 also fed back negatively on expression of jasmonate biosynthesis pathway genes to decrease flower jasmonate level, which correlated with termination of growth after flowers have opened. These dynamic feedbacks may promote timely, coordinated, and transient growth of flower organs.

Arabidopsis AtVPS15 plays essential roles in pollen germination possibly by interacting with AtVPS34

VPS15 protein is a component of the phosphatidylinositol 3-kinase complex which plays a pivotal role in the development of yeast and mammalian cells. The knowledge about the function of its homologue in plants remains limited. Here we report that AtVPS15, a homologue of yeast VPS15p in Arabidopsis, plays an essential role in pollen germination. Homozygous T-DNA insertion mutants of AtVPS15 could not be obtained from the progenies of self-pollinated heterozygous mutants. Reciprocal crosses between atvps15 mutants and wild-type Arabidopsis revealed that the T-DNA insertion was not able to be transmitted by male gametophytes. DAPI staining, Alexander's stain and scanning electron microscopic analysis showed that atvps15 heterozygous plants produced pollen grains that were morphologically indistinguishable from wild-type pollen, whereas in vitro germination experiments revealed that germination of the pollen grains was defective. GUS staining analysis of transgenic plants expressing the GUS reporter gene driven by the AtVPS15 promoter showed that AtVPS15 was mainly expressed in pollen grains. Finally, DUALmembrane yeast two-hybrid analysis demonstrated that AtVPS15 might interact directly with AtVPS34. These results suggest that AtVPS15 is very important for pollen germination, possibly through modulation of the activity of PI3-kinase.

Fine mapping and candidate gene prediction of the photoperiod and thermo-sensitive genic male sterile gene pms1(t) in rice

Pei'ai64S, an indica sterile variety with photoperiod and thermo-sensitive genic male sterile (PTGMS) genes, has been widely exploited for commercial seed production for "two-line" hybrid rice in China. One PTGMS gene from Pei'ai64S, pms1(t), was mapped by a strategy of bulked-extreme and recessive-class approach with simple sequence repeat (SSR) and insert and deletion (In-Del) markers. Using linkage analysis for the F(2) mapping population consisting of 320 completely male sterile individuals derived from a cross between Pei'ai64S and 93-11 (indica restorer) lines, the pms1(t) gene was delimited to the region between the RM21242 (0.2 cM) and YF11 (0.2 cM) markers on the short arm of chromosome 7. The interval containing the pms1(t) locus, which was co-segregated with RM6776, is a 101.1 kb region based on the Nipponbare rice genome. Fourteen predicted loci were found in this region by the Institute for Genomic Research (TIGR) Genomic Annotation. Based on the function of the locus LOC_Os07g12130 by bioinformatics analysis, it is predicted to encode a protein containing a Myb-like DNA-binding domain, and may process the transcript with thermosensory response. The reverse transcription-polymerase chain reaction (RT-PCR) results revealed that the mRNA levels of LOC_Os07g12130 were altered in different photoperiod and temperature treatments. Thus, the LOC_Os07g12130 locus is the most likely candidate gene for pms1(t). These results may facilitate not only using the molecular marker assisted selection of PTGMS genes, but also cloning of the pms1(t) gene itself.

EOBII controls flower opening by functioning as a general transcriptomic switch

R2R3-MYB transcription factors (TFs) are involved in diverse aspects of plant biology. Recently an R2R3-MYB was identified in Petunia x hybrida line P720 to have a role in the transcriptional regulation of floral volatile production. We propose a more foundational role for the R2R3-MYB TF EMISSION OF BENZENOIDS II (EOBII). The homolog of EOBII was isolated and characterized from P. x hybrida 'Mitchell Diploid' (MD) and Nicotiana attenuata. For both MD and N. attenuata, EOBII transcript accumulates to high levels in floral tissue with maximum accumulation at flower opening. When EOBII transcript levels are severely reduced using a stable RNAi (ir) approach in MD and N. attenuata, ir-EOBII flowers fail to enter anthesis and prematurely senesce. Transcript accumulation analysis demonstrated core phenylpropanoid pathway transcripts and cell wall modifier transcript levels are altered in ir-EOBII flowers. These flowers can be partially complemented by feeding with a sucrose, t-cinnamic acid, and gibberellic acid solution; presumably restoring cellular aspects sufficient for flower opening. Additionally, if ethylene sensitivity is blocked in either MD or N. attenuata, ir-EOBII flowers enter anthesis. These experiments demonstrate one R2R3-MYB TF can control a highly dynamic process fundamental to sexual reproduction in angiosperms: the opening of flowers.

The final split: the regulation of anther dehiscence

Controlling male fertility is an important goal for plant reproduction and selective breeding. Hybrid vigour results in superior growth rates and increased yields of hybrids compared with inbred lines; however, hybrid generation is costly and time consuming. A better understanding of anther development and pollen release will provide effective mechanisms for the control of male fertility and for hybrid generation. Male sterility is associated not only with the lack of viable pollen, but also with the failure of pollen release. In such instances a failure of anther dehiscence has the advantage that viable pollen is produced, which can be used for subsequent rescue of fertility. Anther dehiscence is a multistage process involving localized cellular differentiation and degeneration, combined with changes to the structure and water status of the anther to facilitate complete opening and pollen release. After microspore release the anther endothecium undergoes expansion and deposition of ligno-cellulosic secondary thickening. The septum separating the two locules is then enzymatically lysed and undergoes a programmed cell death-like breakdown. The stomium subsequently splits as a consequence of the stresses associated with pollen swelling and anther dehydration. The physical constraints imposed by the thickening in the endothecium limit expansion, placing additional stress on the anther, so as it dehydrates it opens and the pollen is released. Jasmonic acid has been shown to be a critical signal for dehiscence, although other hormones, particularly auxin, are also involved. The key regulators and physical constraints of anther dehiscence are discussed.

The Jasmonate-ZIM domain proteins interact with the R2R3-MYB transcription factors MYB21 and MYB24 to affect Jasmonate-regulated stamen development in Arabidopsis

The Arabidopsis thaliana F-box protein CORONATINE INSENSITIVE1 (COI1) perceives jasmonate (JA) signals and subsequently targets the Jasmonate-ZIM domain proteins (JAZs) for degradation by the SCF(COI1)-26S proteasome pathway to mediate various jasmonate-regulated processes, including fertility, root growth, anthocyanin accumulation, senescence, and defense. In this study, we screened JAZ-interacting proteins from an Arabidopsis cDNA library in the yeast two-hybrid system. MYB21 and MYB24, two R2R3-MYB transcription factors, were found to interact with JAZ1, JAZ8, and JAZ11 in yeast and in planta. Genetic and physiological experiments showed that the myb21 myb24 double mutant exhibited defects specifically in pollen maturation, anther dehiscence, and filament elongation leading to male sterility. Transgenic expression of MYB21 in the coi1-1 mutant was able to rescue male fertility partially but unable to recover JA-regulated root growth inhibition, anthocyanin accumulation, and plant defense. These results demonstrate that the R2R3-MYB transcription factors MYB21 and MYB24 function as direct targets of JAZs to regulate male fertility specifically. We speculate that JAZs interact with MYB21 and MYB24 to attenuate their transcriptional function; upon perception of JA signal, COI1 recruits JAZs to the SCF(COI1) complex for ubiquitination and degradation through the 26S proteasome; MYB21 and MYB24 are then released to activate expression of various genes essential for JA-regulated anther development and filament elongation.

Ectopic expression of MYB46 identifies transcriptional regulatory genes involved in secondary wall biosynthesis in Arabidopsis

MYB46 functions as a transcriptional switch that turns on the genes necessary for secondary wall biosynthesis. Elucidating the transcriptional regulatory network immediately downstream of MYB46 is crucial to our understanding of the molecular and biochemical processes involved in the biosynthesis and deposition of secondary walls in plants. To gain insights into MYB46-mediated transcriptional regulation, we first established an inducible secondary wall thickening system in Arabidopsis by expressing MYB46 under the control of dexamethasone-inducible promoter. Then, we used an ATH1 GeneChip microarray and Illumina digital gene expression system to obtain a series of transcriptome profiles with regard to the induction of secondary wall development. These analyses allowed us to identify a group of transcription factors whose expression coincided with or preceded the induction of secondary wall biosynthetic genes. A transient transcriptional activation assay was used to confirm the hierarchical relationships among the transcription factors in the network. The in vivo assay showed that MYB46 transcriptionally activates downstream target transcription factors, three of which (AtC3H14, MYB52 and MYB63) were shown to be able to activate secondary wall biosynthesis genes. AtC3H14 activated the transcription of all of the secondary wall biosynthesis genes tested, suggesting that AtC3H14 may be another master regulator of secondary wall biosynthesis. The transcription factors identified here may include direct activators of secondary wall biosynthesis genes. The present study discovered novel hierarchical relationships among the transcription factors involved in the transcriptional regulation of secondary wall biosynthesis, and generated several testable hypotheses.

The MYB305 transcription factor regulates expression of nectarin genes in the ornamental tobacco floral nectary

We have isolated and characterized the cDNA encoding the ornamental tobacco (Nicotiana langsdorffii X N. sanderae) homolog of the antirrhinum (Antirrhinum majus) MYB305. This transcription factor was robustly expressed at Stage 12 of nectary development but was only weakly expressed in the earlier Stage 6 nectaries. The ornamental tobacco MYB305 contains a conserved R2R3 MYB DNA binding domain with 76 amino acids in the activation domain. A green fluorescent protein-MYB305 fusion localized to nucleus of tobacco protoplasts and yeast one-hybrid assays demonstrated that it functions as a transcription activator. A conserved 23-amino acid C-terminal domain is required to activate gene expression. The coding region of the myb305 cDNA was expressed in Escherichia coli as a glutathione S-transferase fusion protein and was purified to homogeneity. This protein shows binding to two consensus MYB binding sites on the ornamental tobacco Nectarin I (nec1) promoter as well as to the single site located on the Nectarin V (nec5) promoter. Deletions of either of the binding sites from the nec1 promoter significantly reduced expression in nectary tissues. Temporally, MYB305 expression precedes that of nec1 and nec5, as would be expected if the MYB305 factor regulates expression of the nec1 and nec5 genes. Ectopic expression of MYB305 in foliage was able to induce expression of both nec1 and nec5, as well as two flavonoid biosynthetic genes in the foliage. Finally, RNA interference knockdown of MYB305 resulted in reduced expression of both nectarins and flavonoid biosynthetic genes. We conclude that expression of MYB305 regulates expression of the major nectarin genes in the floral nectary.

Gibberellin acts through jasmonate to control the expression of MYB21, MYB24, and MYB57 to promote stamen filament growth in Arabidopsis

Precise coordination between stamen and pistil development is essential to make a fertile flower. Mutations impairing stamen filament elongation, pollen maturation, or anther dehiscence will cause male sterility. Deficiency in plant hormone gibberellin (GA) causes male sterility due to accumulation of DELLA proteins, and GA triggers DELLA degradation to promote stamen development. Deficiency in plant hormone jasmonate (JA) also causes male sterility. However, little is known about the relationship between GA and JA in controlling stamen development. Here, we show that MYB21, MYB24, and MYB57 are GA-dependent stamen-enriched genes. Loss-of-function of two DELLAs RGA and RGL2 restores the expression of these three MYB genes together with restoration of stamen filament growth in GA-deficient plants. Genetic analysis showed that the myb21-t1 myb24-t1 myb57-t1 triple mutant confers a short stamen phenotype leading to male sterility. Further genetic and molecular studies demonstrate that GA suppresses DELLAs to mobilize the expression of the key JA biosynthesis gene DAD1, and this is consistent with the observation that the JA content in the young flower buds of the GA-deficient quadruple mutant ga1-3 gai-t6 rga-t2 rgl1-1 is much lower than that in the WT. We conclude that GA promotes JA biosynthesis to control the expression of MYB21, MYB24, and MYB57. Therefore, we have established a hierarchical relationship between GA and JA in that modulation of JA pathway by GA is one of the prerequisites for GA to regulate the normal stamen development in Arabidopsis.