Abscisic Acid Signal Transduction Research Articles

Characterization and expression of abscisic acid signal transduction genes during mulberry fruit ripening

The plant hormone abscisic acid (ABA) plays an important role in fruit development. To analyze the transcriptional regulation of ABA signaling pathway-related genes during mulberry (Morus alba L.) fruit development and ripening, 17 genes participating in ABA signal transduction were isolated from the Morus notabilis genome database, including five MnPYL, six MnPP2C, and six MnSnRK2 genes. The result of multiple sequence alignment revealed that their functional amino acid residues and domains are conserved within each gene family. The expression profiles of ABA signaling pathway-related genes in the fruit of Morus atropurpurea cv. Jialing No. 40 were measured by quantitative real-time polymerase chain reaction. The transcripts of MaPYL4, MaPP2C5, and MaSnRK2.6 were expressed at a relatively higher level during the entire development process. Moreover, the transcript levels of MaPYL1/3/5, MaPP2C2/4/5/6, and MaSnRK2.3/2.6 were lower during the early-maturation stage and higher during the post-maturation stage, which suggests that they may play a vital role in regulating mulberry fruit ripening. In addition, these genes showed strong responses to exogenous ABA, fluridone, glucose, and sucrose. This study also indicated that exogenous ABA, sucrose, and glucose may promote fruit maturity, while fluridone significantly inhibits fruit ripening.

Abscisic acid negatively regulates post-penetration resistance of Arabidopsis to the biotrophic powdery mildew fungus.

Pytohormone abscisic acid (ABA) plays important roles in defense responses. Nonetheless, how ABA regulates plant resistance to biotrophic fungi remains largely unknown. Arabidopsis ABA-deficient mutants, aba2-1 and aba3-1, displayed enhanced resistance to the biotrophic powdery mildew fungus Golovinomyces cichoracearum. Moreover, exogenously administered ABA increased the susceptibility of Arabidopsis to G. cichoracearum. Arabidopsis ABA perception components mutants, abi1-1 and abi2-1, also displayed similar phenotypes to ABA-deficient mutants in resistance to G. cichoracearum. However, the resistance to G. cichoracearum is not changed in downstream ABA signaling transduction mutants, abi3-1, abi4-1, and abi5-1. Microscopic examination revealed that hyphal growth and conidiophore production of G. cichoracearum were compromised in the ABA deficient mutants, even though pre-penetration and penetration growth of the fungus were not affected. In addition, salicylic acid (SA) and MPK3 are found to be involved in ABA-regulated resistance to G. cichoracearum. Our work demonstrates that ABA negatively regulates post-penetration resistance of Arabidopsis to powdery mildew fungus G. cichoracearum, probably through antagonizing the function of SA.

Production of ABA responses requires both the nuclear and cytoplasmic functional involvement of PYR1

Abscisic acid (ABA) enhances stress tolerant responses in plants against unfavorable environmental conditions. In Arabidopsis, ABA promotes interactions between PYR/PYL/RCARs and PP2C, thereby allowing SnRK2s to phosphorylate downstream components required for the regulation of gene expression or for gating ion channels. Because PYR1 is known to localize to nucleus and cytoplasm it is a question whether nuclear or cytoplasmic PYR1 confer different functions to the ABA signaling pathway, as has been previously shown for regulatory proteins. In order to answer this question, transgenic lines expressing nuclear PYR1 were generated in an ABA insensitive mutant background. Enforced nuclear expression of PYR1 was examined by confocal microscopy and western blot analysis. Physiological analyses of the transgenic lines demonstrated that nuclear PYR1 is sufficient to generate ABA responses, such as, the inhibition of seed germination, root growth inhibition, the induction of gene expression, and stomatal closing movement. However, for the full recovery of ABA responses in the mutant background cytoplasmic PYR1 was required. The study suggests both nuclear and cytoplasmic PYR1 participate in the control of ABA signal transduction.

A Comprehensive Proteomic Survey of ABA-Induced Protein Phosphorylation in Rice (Oryza sativa L.)

abscisic acid (ABA) is a key phytohormone regulating plant development and stress response. The signal transduction of ABA largely relies on protein phosphorylation. However; little is known about the phosphorylation events occurring during ABA signaling in rice thus far. By employing a label-free; MS (Mass Spectrometry)-based phosphoproteomic approach; we identified 2271 phosphosites of young rice seedlings and their intensity dynamics in response to ABA; during which 1060 proteins were found to be differentially phosphorylated. Western-blot analysis verified the differential phosphorylation pattern of D1, SMG1 and SAPK9 as indicated by the MS result; suggesting the high reliability of our phosphoproteomic data. The DP (differentially phosphorylated) proteins are extensively involved in ABA as well as other hormone signaling pathways. It is suggested that ABA antagonistically regulates brassinosteroid (BR) signaling via inhibiting BR receptor activity. The result of this study not only expanded our knowledge of rice phosphoproteome, but also shed more light on the pattern of protein phosphorylation in ABA signaling.

Plant Defense Response to Abiotic Stress via Abscisic Acid Signaling Pathway

Plants are exposed to stresses such as pathogens, drought, high salt and temperature stress, and have evolved and developed diverse and sophisticated defense mechanisms to protect themselves from these stresses. Many hormones are involved in the metabolism of plants and some are known to affect the control of plant defense mechanisms against pathogen infection and environmental stress. In biotic and abiotic stress responses, abscisic acid (ABA) regulates key metabolic pathways. In abiotic stress conditions, plants induce ABA biosynthesis, which activate defense response at the cellular level, such as expression of stress-related genes and stomatal closure. Moreover, the molecular components related to ABA signal transduction have been identified and complex networks of interactions are being analyzed in detail. In this review, I will describe the ABA signal transduction pathway from the ABA receptor to the ion channel and provide basic information on the current understanding of the plant defense response to abiotic stress via the ABA signal transduction pathway.

Overexpression of Poplar Pyrabactin Resistance-Like Abscisic Acid Receptors Promotes Abscisic Acid Sensitivity and Drought Resistance in Transgenic Arabidopsis.

Drought stress is an important environmental factor limiting productivity of plants, especially fast growing species with high water consumption like poplar. Abscisic acid (ABA) is a phytohormone that positively regulates seed dormancy and drought resistance. The PYR1 (Pyrabactin Resistance 1)/ PYRL (PYR-Like)/ RCAR (Regulatory Component of ABA Receptor) (PYR/PYL/RCAR) ABA receptor family has been identified and widely characterized in Arabidopsis thaliana. However, their functions in poplars remain unknown. Here, we report that 2 of 14 PYR/PYL/RCAR orthologues in poplar (Populus trichocarpa) (PtPYRLs) function as a positive regulator of the ABA signal transduction pathway. The Arabidopsis transient expression and yeast two-hybrid assays showed the interaction among PtPYRL1 and PtPYRL5, a clade A protein phosphatase 2C, and a SnRK2, suggesting that a core signalling complex for ABA signaling pathway exists in poplars. Phenotypic analysis of PtPYRL1 and PtPYRL5 transgenic Arabidopsis showed that these two genes positively regulated the ABA responses during the seed germination. More importantly, the overexpression of PtPYRL1 and PtPYRL5 substantially improved ABA sensitivity and drought stress tolerance in transgenic plants. In summary, we comprehensively uncovered the properties of PtPYRL1 and PtPYRL5, which might be good target genes to genetically engineer drought-Resistant plants.

Arabidopsis thaliana RECEPTOR DEAD KINASE1 Functions as a Positive Regulator in Plant Responses to ABA

Abscisic acid (ABA) is a major phytohormone involved in important stress-related and developmental plant processes. Membrane-delimited ABA signal transduction plays an important role in early ABA signaling, but the molecular mechanisms connecting core signaling components to the plasma membrane remain unclear. Plants have evolved a large number of receptor-like kinases (RLKs) to modulate diverse biological processes by perceiving extracellular stimuli and activating downstream signaling responses. In this study, a putative leucine-rich repeat-RLK gene named RECEPTOR DEAD KINASE1 (AtRDK1) was identified and characterized in Arabidopsis thaliana. RDK1 promoter–GUS analysis revealed that RDK1 is expressed ubiquitously in the various tissues in Arabidopsis, and its expression is mainly induced by ABA. In the presence of ABA, RDK1-deficient rdk1-1 and rdk1-2 lines showed significant resistance in cotyledon greening and root growth, whereas RDK1-overexpressing lines showed enhanced sensitivity. Consistently, the expression of ABA-responsive genes was significantly downregulated in rdk1 mutant seedlings, which were also hypersensitive to drought stress with increased water loss. Interestingly, RDK1 was found to be an atypical kinase localized to the plasma membrane and did not require its kinase activity during ABA-mediated inhibition of seedling development. Accordingly, RDK1 interacted in the plasma membrane with type 2C protein phosphatase ABSCISIC ACID INSENSITIVE1 (ABI1); this interaction was further enhanced by exogenous application of ABA, suggesting that RDK1-mediated recruitment of ABI1 onto the plasma membrane is important for ABA signaling. Taken together, these results reveal an important role for RDK1 in plant responses to abiotic stress conditions in an ABA-dependent manner.

Variation in pre-harvest sprouting resistance, seed germination and changes in abscisic acid levels during grain development in diverse rice genetic resources

AbstractAmong domesticated traits, pre-harvest sprouting (PHS) caused by the early breakage of dormancy leads to severe economic losses. Therefore, regulating PHS is important for cereal crop improvement against changes in climate. In this study, we surveyed naturally occurring variations in seed germination in diverse rice germplasm for the available resources of this trait, and investigated the changes of abscisic acid (ABA) levels during grain development by the distinguished PHS-resistant groups. We discovered wide variations in germination among the 205 rice accessions examined and found that 90 accessions are resistant (germination <20%) to PHS. Tropical and subtropical accessions, which are subjected to long wet periods, are more resistant to PHS than the other accessions. We detected an increase in germination of detached seeds from the panicle compared with intact seeds in panicle at harvesting time. This might be attributed to a weakening of the mechanical barrier that prevents water imbibition and radical emergence. ABA levels were maximal at 10 d after flowering and decreased thereafter. Interestingly, PHS-susceptible accessions maintained higher or similar ABA levels compared with PHS-resistant accessions, suggesting that the key factors for seed dormancy and its breakage are ABA perception and signal transduction rather than total ABA content. The diversity of germination ability detected in this study could be sustainably used for crop improvement and to help unveil the genetic and physiological basis of this quantitative trait.

Potential role of D-myo-inositol-3-phosphate synthase and 14-3-3 genes in the crosstalk between Zea mays and Rhizophagus intraradices under drought stress.

Arbuscular mycorrhizal (AM) symbiosis is known to stimulate plant drought tolerance. However, the mechanisms underlying the synergistic responses of the symbiotic partners to drought stress are largely unknown. A split-root experiment was designed to investigate the molecular interactions between a host plant and an AM fungus (AMF) under drought stress. In the two-compartment cultivation system, an entire or only a half root system of a maize plant was inoculated with an AMF, Rhizophagus intraradices, in the presence of localized or systemic drought treatment. Plant physiological parameters including growth, water status, and phosphorus concentration, and the expression of drought tolerance-related genes in both roots and R. intraradices were recorded. Although mycorrhizal inoculation in either one or both compartments systemically decreased abscisic acid (ABA) content in the whole root system subjected to systemic or local drought stress, we observed local and/or systemic AM effects on root physiological traits and the expression of functional genes in both roots and R. intraradices. Interestingly, the simultaneous increase in the expression of plant genes encoding D-myo-inositol-3-phosphate synthase (IPS) and 14-3-3-like protein GF14 (14-3GF), which were responsible for ABA signal transduction, was found to be involved in the activation of 14-3-3 protein and aquaporins (GintAQPF1 and GintAQPF2) in R. intraradices. These findings suggest that coexpression of IPS and 14-3GF is responsible for the crosstalk between maize and R. intraradices under drought stress, and potentially induces the synergistic actions of the symbiotic partners in enhancing plant drought tolerance.

Comparison of phytohormone biosynthesis and signal transduction pathways in developing and abortive hazelnut ovules

In hazelnuts, ovule abortion is associated with the formation of empty nuts, resulting in serious yield losses. Phytohormones play important roles in plant growth and development; however, the mechanisms through which they regulate ovule abortion in hazelnut are largely unknown. RNA-seq identified 1209 differentially expressed genes with Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway annotation between developing and abortive ovules in hazelnut. Hormone signal transduction (ko04075), and several phytohormone biosynthesis pathways, were found to be significantly enriched after pathway enrichment analysis. Compared with developing ovules, the levels of indole-3-acetic acid (IAA), gibberellins (GA), cytokinin (CTK), and salicylic acid (SA) were found to be significantly lower in abortive ovules, while levels of abscisic acid (ABA), ethylene (ETH), and jasmonic acid (JA) were found to be significantly higher. Consistent with these results, some important rate-limiting enzymes involved in the biosynthesis of phytohormones, including 9-cis-epoxycarotenoid dioxygenase, ACC synthase, and phospholipase A1 were significantly up-regulated in abortive ovules. Some key genes in the ETH, JA, and ABA signal transduction pathways were highly upregulated, including ethylene-responsive transcription factor 1 (ERF1/2) and the serine/threonine-protein kinase CTR1 in the ETH signal pathway, jasmonate ZIM domain-containing protein (JAZ) and the transcription factor MYC2 in the JA signal pathway, and ABA responsive element binding factor (ABF) in the JA signal pathway. Thus, ABA, ETH, and JA signaling were more active in abortive ovules than in developing ovules. Expression levels of NCED, ABF, ACS, ERF1/2, PLA1, and MYC2 revealed by q-RT-PCR were consistent with the results obtained by differentially expressed genes (DEG) analysis. Our data suggest that multiple phytohormone signaling pathways are involved in the development of hazelnut ovules. Inhibition of IAA, GA, CTK, and SA biosynthesis and signaling pathways, and activation of ABA, ETH, and JA biosynthesis and signaling pathways may contribute to the formation of abortive ovules in hazelnut.

Comparative Transcriptome Analysis between Low- and High-Cadmium-Accumulating Genotypes of Pakchoi (Brassica chinensis L.) in Response to Cadmium Stress.

To reduce cadmium (Cd) pollution of food chains, screening and breeding of low-Cd-accumulating cultivars are the focus of much study. Two previously identified genotypes, a low-Cd-accumulating genotype (LAJK) and a high-Cd-accumulating genotype (HAJS) of pakchoi (Brassica chinesis L.), were stressed by Cd (12.5 μM) for 0 h (T0), 3 h (T3) and 24 h (T24). By comparative transcriptome analysis for root tissue, 3005 and 4343 differentially expressed genes (DEGs) were identified in LAJK at T3 (vs T0) and T24 (vs T3), respectively, whereas 8677 and 5081 DEGs were detected in HAJS. Gene expression pattern analysis suggested a delay of Cd responded transcriptional changes in LAJK compared to HAJS. DEG functional enrichments proposed genotype-specific biological processes coped with Cd stress. Cell wall biosynthesis and glutathione (GSH) metabolism were found to involve in Cd resistance in HAJS, whereas DNA repair and abscisic acid (ABA) signal transduction pathways played important roles in LAJK. Furthermore, the genes participating in Cd efflux such as PDR8 were overexpressed in LAJK, whereas those responsible for Cd transport such as YSL1 were more enhanced in HAJS, exhibiting different Cd transport processes between two genotypes. These novel findings should be useful for molecular assisted screening and breeding of low-Cd-accumulating genotypes for pakchoi.

Release of GTP Exchange Factor Mediated Down-Regulation of Abscisic Acid Signal Transduction through ABA-Induced Rapid Degradation of RopGEFs.

The phytohormone abscisic acid (ABA) is critical to plant development and stress responses. Abiotic stress triggers an ABA signal transduction cascade, which is comprised of the core components PYL/RCAR ABA receptors, PP2C-type protein phosphatases, and protein kinases. Small GTPases of the ROP/RAC family act as negative regulators of ABA signal transduction. However, the mechanisms by which ABA controls the behavior of ROP/RACs have remained unclear. Here, we show that an Arabidopsis guanine nucleotide exchange factor protein RopGEF1 is rapidly sequestered to intracellular particles in response to ABA. GFP-RopGEF1 is sequestered via the endosome-prevacuolar compartment pathway and is degraded. RopGEF1 directly interacts with several clade A PP2C protein phosphatases, including ABI1. Interestingly, RopGEF1 undergoes constitutive degradation in pp2c quadruple abi1/abi2/hab1/pp2ca mutant plants, revealing that active PP2C protein phosphatases protect and stabilize RopGEF1 from ABA-mediated degradation. Interestingly, ABA-mediated degradation of RopGEF1 also plays an important role in ABA-mediated inhibition of lateral root growth. The presented findings point to a PP2C-RopGEF-ROP/RAC control loop model that is proposed to aid in shutting off ABA signal transduction, to counteract leaky ABA signal transduction caused by “monomeric” PYL/RCAR ABA receptors in the absence of stress, and facilitate signaling in response to ABA.

Contrasting transcriptional responses of PYR1/PYL/RCAR ABA receptors to ABA or dehydration stress between maize seedling leaves and roots.

BackgroundThe different actions of abscisic acid (ABA) in the aboveground and belowground parts of plants suggest the existence of a distinct perception mechanism between these organs. Although characterization of the soluble ABA receptors PYR1/PYL/RCAR as well as core signaling components has greatly advanced our understanding of ABA perception, signal transduction, and responses, the environment-dependent organ-specific sensitivity of plants to ABA is less well understood.ResultsBy performing real-time quantitative PCR assays, we comprehensively compared transcriptional differences of core ABA signaling components in response to ABA or osmotic/dehydration stress between maize (Zea mays L.) roots and leaves. Our results demonstrated up-regulation of the transcript levels of ZmPYLs homologous to dimeric-type Arabidopsis ABA receptors by ABA in maize primary roots, whereas those of ZmPYLs homologous to monomeric-type Arabidopsis ABA receptors were down-regulated. However, this trend was reversed in the leaves of plants treated with ABA via the root medium. Although the mRNA levels of ZmPYL1-3 increased significantly in roots subjected to polyethylene glycol (PEG)-induced osmotic stress, ZmPYL4-11 transcripts were either maintained at a stable level or increased only slightly. In detached leaves subjected to dehydration, the transcripts of ZmPYL1-3 together with ZmPYL5, ZmPYL6, ZmPYL10 and ZmPYL11 were decreased, whereas those of ZmPYL4, ZmPYL7 and ZmPYL8 were significantly increased. Our results also showed that all of the evaluated transcripts of PP2Cs and SnRK2 were quickly up-regulated in roots by ABA or osmotic stress; conversely they were either up-regulated or maintained at a constant level in leaves, depending on the isoforms within each family.ConclusionsThere is a distinct profile of PYR/PYL/RCAR ABA receptor gene expression between maize roots and leaves, suggesting that monomeric-type ABA receptors are mainly involved in the transmission of ABA signals in roots but that dimeric-type ABA receptors primarily carry out this function in leaves. Given that ZmPYL1 and ZmPYL4 exhibit similar transcript abundance under normal conditions, our findings may represent a novel mechanism for species-specific regulation of PYR/PYL/RCAR ABA receptor gene expression. A difference in the preference for core signaling components in the presence of exogenous ABA versus stress-induced endogenous ABA was observed in both leaves and roots. It appears that core ABA signaling components perform their osmotic/dehydration stress response functions in a stress intensity-, duration-, species-, organ-, and isoform-specific manner, leading to plasticity in response to adverse conditions and, thus, acclimation to life on land. These results deepen our understanding of the diverse biological effects of ABA between plant leaves and roots in response to abiotic stress at the stimulus-perception level.Electronic supplementary materialThe online version of this article (doi:10.1186/s12870-016-0764-x) contains supplementary material, which is available to authorized users.

Differential Activation of the Wheat SnRK2 Family by Abiotic Stresses.

Plant responses to stress occur via abscisic acid (ABA) dependent or independent pathways. Sucrose non-fermenting1-related protein kinase 2 (SnRK2) play a key role in plant stress signal transduction pathways. It is known that some SnRK2 members are positive regulators of ABA signal transduction through interaction with group A type 2C protein phosphatases (PP2Cs). Here, 10 SnRK2s were isolated from wheat. Based on phylogenetic analysis using kinase domains or the C-terminus, the 10 SnRK2s were divided into three subclasses. Expression pattern analysis revealed that all TaSnRK2s were involved in the responses to PEG, NaCl, and cold stress. TaSnRK2s in subclass III were strongly induced by ABA. Subclass II TaSnRK2s responded weakly to ABA, whereas TaSnRK2s in subclass I were not activated by ABA treatment. Motif scanning in the C-terminus indicated that motifs 4 and 5 in the C-terminus were unique to subclass III. We further demonstrate the physical and functional interaction between TaSnRK2s and a typical group A PP2C (TaABI1) using Y2H and BiFC assays. The results showed that TaABI1 interacted physically with subclass III TaSnRK2s, while having no interaction with subclasses I and II TaSnRK2s. Together, these findings indicated that subclass III TaSnRK2s were involved in ABA regulated stress responses, whereas subclasses I and II TaSnRK2s responded to various abiotic stressors in an ABA-independent manner.

Effects of exogenous abscisic acid on the expression of citrus fruit ripening-related genes and fruit ripening

Despite exogenous abscisic acid (ABA) treatment is a widely-used effective method to prove its role in plants, this method has been limitedly explored in citrus fruits. Here, we examined the effects of exogenous ABA and nordihydroguaiaretic acid (NDGA) on the color index H value and the contents of soluble sugars, organic acids and endogenous hormones in the fruits of Citrus reticulata Blanco cv. Ponkan. Additionally, the expression profiles of genes involved in the ABA, sugar and organic acid metabolism and signal transduction pathway in fruits were also investigated. The results indicated that exogenous ABA could accelerate fruit coloring, significantly decrease the organic acid content, and affect the ripening of citrus fruit, while treatment with NDGA could restrain fruit coloring and acid degradation. Exogenous ABA treatment produced minor effect on the accumulation of sugars but largely regulated the expression of most sugar- and acid-related genes, indicating a coordinate interaction between the ABA signaling pathway and sucrose signaling pathway to regulate citrus fruit ripening. Especially, CsSUC 3 plays a vital role in accumulation of sugars during the last ripening stage of citrus fruit, which could be induced by ABA treatment. The transcript levels of CsACO1 and CsNADP-IDH in ABA-treated fruits were significantly higher than in the control fruits during the late ripening stages, which was conducive to the degradation of organic acids. Moreover, ABA could restrict its own accumulation at 14 DAY not only by inducing the expression of ABA 8′-hydroxylase 1 but also by reducing the expression of CsNCED1, and the transcriptional levels of other ABA-related genes were largely triggered by exogenous ABA. Overall, ABA is a positive regulator of ripening and could be used to regulate citrus fruit ripening effectively.

Studies on creation of specific regulators for abscisic acid catabolism and signal transduction

Studies on creation of specific regulators for abscisic acid catabolism and signal transduction

Molecular Cloning of ZmPP6C Gene and Its Ex-pression Patterns in Response to Light and Stress Treatments in Maize( Zea mays L.)

PP6C is the catalytic subunits of Ser/Thr protein phosphatase 6 (PP6) gene, which plays important roles in auxin transport polarity, ABA (abscisic acid) signal transduction, flowering time control though light signaling pathway. To clarify structural characteristics of PP6C protein and the evolution relationships among plant PP6C homologs, we cloned ZmPP6C gene by RT-PCR. The open reading frame (ORF) of ZmPP6C possesses 912 nucleotides and encodes 303 amino acid residues with one PP2Ac domain (the catalytic subunits of Ser/Thr protein phosphatase 2A). Phylogenetic analysis indicated that ZmPP6C belongs to the same branch with the PP6C of Sorghum bicolor, and shows high similarity to all PP6C proteins from other monocotyledons and dicotyledons. Further quantitative RT-PCR (qRT-PCR) assays indicated that ZmPP6C was highly expressed in leaf and lowly 第 2期 原换换等: 玉米 ZmPP6C基因的克隆及其响应光质和胁迫处理的表达模式分析 171 in stem, stamen, pulvinus, sheath, and pedical. ZmPP6C transcription abundances could respond to different light and circadian treatments (both long-day and short-day conditions), especially to the light transitions from the dark to far-red or red light condition. In addition, ZmPP6C transcription abundances were up-regulated by high osmosis, high salt and water logging. Our results suggested that ZmPP6C may be involved in light signaling pathway, flowering time control, and abiotic stress response in maize, and its roles in crop improvement are worthy of more exploration in the future.

De novo sequencing and analysis of root transcriptome to reveal regulation of gene expression by moderate drought stress in Glycyrrhiza uralensis

Moderate drought stress has been found to promote the accumulation of active ingredients in Glycyrrhiza uralensis root and hence improve the medicinal quality. In this study, the transcriptomes of 6-month-old moderate drought stressed and control G. uralensis root (the relative water content in soil was 40%-45% and 70%-75%, respectively) were sequenced using Illumina HiSeq 2000. A total of 80,490 490 and 82 588 278 clean reads, 94,828 and 305,100 unigenes with N50 sequence of 1,007 and 1,125 nt were obtained in drought treated and control transcriptome, respectively. Differentially expressed genes analysis revealed that the genes of some cell wall enzymes such as β-xylosidase, legumain and GDP-L-fucose synthase were down-regulated indicating that moderate drought stress might inhibit the primary cell wall degradation and programmed cell death in root cells. The genes of some key enzymes involved in terpenoid and flavonoid biosynthesis were up-regulated by moderate drought stress might be the reason for the enhancement for the active ingredients accumulation in G. uralensis root. The promotion of the biosynthesis and signal transduction of auxin, ethylene and cytokinins by moderate drought stress might enhance the root formation and cell proliferation. The promotion of the biosynthesis and signal transduction of abscisic acid and jasmonic acid by moderate drought stress might enhance the drought stress tolerance in G. uralensis. The inhibition of the biosynthesis and signal transduction of gibberellin and brassinolide by moderate drought stress might retard the shoot growth in G. uralensis.

Comprehensive quantification and genome survey reveal the presence of novel phytohormone action modes in red seaweeds

Emerging work has suggested the existence of phytohormones in seaweeds, although chemical species, endogenous biosynthetic pathways, and signal transduction machineries remain poorly understood. We performed profiling of nine phytohormones with liquid chromatography-mass spectrometry and in silico genome-wide homology search to identify genes involved in biosynthesis and signal transduction of hormones in red algae. It was demonstrated that two Bangiophycean algae, Bangia fuscopurpurea and Pyropia yezoensis, possessed indoleacetic acid (IAA), N 6-(Δ2-isopentenyl)adenine (iP), abscisic acid (ABA), and salicylic acid, although trans-zeatin, dihydrozeatin, gibberellin A1 and A4, and jasmonate were not detected. Results of genome-wide survey demonstrated that Bangiophycean algae produce iP and ABA via pathways similar to those in terrestrial plants. However, these seaweeds lack homologues of already known factors participating in perception and signal transduction of IAA, iP, ABA and SA, indicating that the action modes of these phytohormones in red seaweeds differ from those elucidated in terrestrial plants. These findings shed lights on evolutional divergence of signal transduction pathways of phytohormones in plants.

Ectopic expression a tomato KNOX Gene Tkn4 affects the formation and the differentiation of meristems and vasculature

The KNOTTED-LIKE HOMEODOMAIN genes are involved in maintenance of the shoot apical meristem which produces the whole above-ground body of vascular plants. In this report, a tomato homolog gene, named as Tkn4 (a nucleus targeted transcription factor) was identified and characterized. By performing RT-PCR, the transcript level of Tkn4 was separately found in stem, root, stamen, stigma, fruit and sepal but hardly visible in the leaf. Besides, Tkn4 was induced by a series of plant hormones. Overexpression of Tkn4 gene in tomato resulted in dwarf phenotype and strongly repressed the formation of shoot apical meristem, lateral meristem and cambiums in transgenic lines. The transgenic lines had wrinkled leaves and anatomic analysis showed that there was no obvious palisade tissues in the leaves and the layer of cells changed in vascular tissue (xylem and phloem). To explore the regulation network of Tkn4, RNA-sequencing was performed in overexpression lines and wild type plants, by which many genes related to the synthesis and the signal transduction of cytokinin, auxin, gibberellin, ethylene, abscisic acid, and tracheary element differentiation or extracellular matrix synthesis were significantly regulated. Taken together, our results demonstrate that Tkn4 plays important roles in regulating the biosynthesis and signal transduction of diverse plant hormones, and the formation and differentiation of meristems and vasculature in tomato.