Regulation of growth and development in phytochrome mutants of <Emphasis Type="Italic">Arabidopsis thaliana</Emphasis> by solar UV

Phytochrome mutants (phyA, phyB and phyAB) of Arabidopsis thaliana were grown under ambient and UV-excluded sunlight to understand their influence on growth and development by mutual exclusion. Phytochrome A and B played a complementary role in the regulation of germination. Suppression of hypocotyl length was predominantly under the control of phytochrome B; UV photoreceptors were active in suppression of hypocotyl growth only in phyB and phyAB mutants. Exclusion of UV promoted the number and the area of rosette leaves only in presence of phytochrome A and B. Phytochrome mutation reduced petiole length, whereas UV exclusion led to an increase. Requirement of long-day period for flowering was removed in the mutants. Under short-day conditions, flowering was predominantly under the control of phytochrome B, since phyB mutants flowered earlier than phyA mutants. Solar UV regulates the number of boltings and number of siliques per plant. Overall biomass of the plants is enhanced by the exclusion of UV only in the wild type. The interaction of phytochromes with UV photoreceptors is discussed in the paper.     

Overexpression of <Emphasis Type="Italic">CCCH</Emphasis> zinc finger protein gene delays flowering time and enhances salt tolerance in Arabidopsis by increasing fatty acid unsaturation

CCCH-type zinc-finger proteins constitute a large family playing key roles during plant development and growth. In the present study, we investigated the involvement of the CCCH-type zinc finger protein of AtZFP1 (At2g25900) in flowering and salt stress response in Arabidopsis. Compared with the wild type (WT), bolting and flowering were delayed in AtZFP1-overexpressing plants. Real-time PCR analysis of floral regulating genes in overexpressing Arabidopsis revealed that enhanced expression of FLC decreased the expressions of FT and SOC1. The Fv/Fm of overexpressing Arabidopsis lines was unchanged under salt stress. In contrast, ΦPSII activity and PSI oxidoreduction decreased in WT, overexpressing and mutant strains under salt stress conditions, with the smallest reduction in these parameters observed in the overexpressing strains. These results suggest that the CCCH zinc-finger protein AtZFP1 primarily controls flowering time by changing the expression of flowering genes under long-day conditions. The overexpression of this protein delayed flowering and increased the content and double-bond index of unsaturated fatty acids. Elevation of unsaturated fatty acid content might play important role in protecting the photosynthetic apparatus and maintaining the membrane function at salt stress by alleviating PSII and PSI photoinhibition.     

<Emphasis Type="Italic">GmDim1</Emphasis> Gene Encodes Nucleolar Localized U5-Small Nuclear Ribonucleoprotein in <Emphasis Type="Italic">Glycine max</Emphasis>

The dim1⁺ gene family is essential for G2/M transition during mitosis and encodes a small nuclear ribonucleoprotein that functions in the mRNA splicing machinery of eukaryotes. However, the plant homolog of DIM1 gene has not been defined yet. Here, we identified a gene named GmDim1 positioned on chromosome 9 of soybean (Glycine max (L.) Merr.) with 80% homology to other eukaryotic dim1⁺ family genes. A domain of soybean DIM1 protein was primarily conserved with U5 snRNP protein family and secondarily aligned with mitotic DIM1 protein family. The GmDim1 gene was expressed constitutively in all soybean organs. The transgenic Arabidopsis thaliana (L.) plants overexpressing GmDim1 showed early flowering and stem elongation, produced multiple shoots and continued flowering after the post-flowering stage. DIM1 proteins transiently expressed in onion cells were localized in the nucleus with dense deposition in the nucleolus. Therefore, we propose that the soybean GmDim1 gene is a component of plant U5 snRNP involved in mRNA splicing and normal progress of plant growth.     

Constitutive expression of <Emphasis Type="Italic">SlTrxF</Emphasis> increases starch content in transgenic <Emphasis Type="Italic">Arabidopsis</Emphasis>

The plastidic thioredoxin F-type (TrxF) protein plays an important role in plant saccharide metabolism. In this study, a gene encoding the TrxF protein, named SlTrxF, was isolated from tomato. The coding region of SlTrxF was cloned into a binary vector under the control of 35S promoter and then transformed into Arabidopsis thaliana. The transgenic Arabidopsis plants exhibited increased starch accumulation compared to the wild-type (WT). Real-time quantitative PCR analysis showed that constitutive expression of SlTrxF up-regulated the expression of ADP-glucose pyrophosphorylase (AGPase) small subunit (AtAGPase-S1 and AtAGPase-S2), AGPase large subunit (AtAGPase-L1 and AtAGPase-L2) and soluble starch synthase (AtSSS I, AtSSS II, AtSSS III and AtSSS IV) genes involved in starch biosynthesis in the transgenic Arabidopsis plants. Meanwhile, enzymatic analyses showed that the major enzymes (AGPase and SSS) involved in the starch biosynthesis exhibited higher activities in the transgenic plants compared to WT. These results suggest that SlTrxF may improve starch content of Arabidopsis by regulating the expression of the related genes and increasing the activities of the major enzymes involved in starch biosynthesis.     

Overexpression of <Emphasis Type="Italic">ThGSTZ1</Emphasis> from <Emphasis Type="Italic">Tamarix hispida</Emphasis> improves tolerance to exogenous ABA and methyl viologen

Key message

Molecular analysis of a zeta subfamily GST gene from T. hispida involved in ABA and methyl viologen tolerance in transgenic Arabidopsis and Tamarix.

Abstract

Glutathione S-transferase (GST) genes are important for the improvement of plant abiotic stress tolerance, and our previous study demonstrated that the ThGSTZ1 gene from Tamarix hispida improves plant salt and drought tolerance. To further understand the role of ThGSTZ1 in the response of plants to abscisic acid (ABA) and oxidative stress, three ThGSTZ1-overexpressing transgenic Arabidopsis thaliana lines were analyzed in the current study. The results showed that the transgenic lines exhibited higher biomass accumulation, higher activities of GST and other protective enzymes, and less reactive oxygen species (ROS) and cell damage than wild-type (WT) plants under ABA and methyl viologen (MV) stress. In addition, the analysis of a transgenic T. hispida line transiently expressing ThGSTZ1 confirmed these results. The activities of GST, glutathione peroxidase, and superoxide dismutase were markedly higher in the ThGSTZ1-overexpressing lines compared with the control lines under both ABA and MV treatments, and the transgenic lines also exhibited a lower degree of electrolyte leakage (EL) and a decreased H₂O₂ content. All these results suggested that ThGSTZ1 can also improve plant ABA and oxidation tolerance by regulating ROS metabolism and that ThGSTZ1 represents an excellent candidate gene for molecular breeding to increase plant stress tolerance.

     

Functional Conservation of an <Emphasis Type="Italic">AGAMOUS</Emphasis> Orthologous Gene Controlling Reproductive Organ Development in the Gymnosperm Species <Emphasis Type="Italic">Taxus chinensis</Emphasis> var. <Emphasis Type="Italic">mairei</Emphasis>

Arabidopsis AGAMOUS (AG) has roles in specifying reproductive organ (stamens and carpels) identity, floral meristem determinacy, and repression of A-function. To investigate possible roles of AG orthologous genes in gymnosperm species and evolution of C function, we isolated and identified AG orthologous gene TcAG from Taxus chinensis var. mairei (family Taxaceae, order Coniferales), a member of the last divergant lineage from higher Conifer that sisters to Gnetales. Sequence alignment and phylogenetic analysis grouped TcAG into the gymnosperm AG lineage. TcAG was expressed in both developing male and female cones, but there was no expression in juvenile leaves. Ectopic expression of TcAG in an Arabidopsis ag mutant produced flowers with the third whorl petaloid stamen and fourth whorl normal carpel, but failed to convert first whorl sepals into carpeloid organs and second whorl petals into stamenoid organs. A 35S::TcAG transgenic Arabidopsis ag mutant had very early flowering, and produced a misshapen inflorescence with a shortened floral axis. Our results suggest that establishment of the complete C-function occurred gradually during AG lineage evolution even in gymnosperms.     

Over-Expression of <Emphasis Type="Italic">PmHSP17.9</Emphasis> in Transgenic <Emphasis Type="Italic">Arabidopsis thaliana</Emphasis> Confers Thermotolerance

Small heat shock proteins (sHSPs) have been shown to be involved in stress tolerance. However, their functions in Prunus mume under heat treatment are poorly characterized. To improve our understanding of sHSPs, we cloned a sHSP gene, PmHSP17.9, from P. mume. Sequence alignment and phylogenetic analysis indicated that PmHSP17.9 was a member of plant cytosolic class III sHSPs. Besides heat stress, PmHSP17.9 was also upregulated by salt, dehydration, oxidative stresses and ABA treatment. Leaves of transgenic Arabidopsis thaliana that ectopically express PmHSP17.9 accumulated less O₂ ^? and H₂O₂ compared with wild type (WT) after 42 °C treatment for 6 h. Over-expression of PmHSP17.9 in transgenic Arabidopsis enhanced seedling thermotolerance by decreased relative electrolyte leakage and MDA content under heat stress treatment when compared to WT plants. In addition, the induced expression of HSP101, HSFA2, and delta 1-pyrroline-5-carboxylate synthase (P5CS) under heat stress was more pronounced in transgenic plants than in WT plants. These results support the positive role of PmHSP17.9 in response to heat stress treatment.     

<Emphasis Type="Italic">ZmFKBP20-1</Emphasis> improves the drought and salt tolerance of transformed Arabidopsis

FK506-binding proteins (FKBPs), which belong to the peptidyl-prolyl cis/trans isomerase superfamily, are involved in plant response to abiotic stresses. A number of FKBP family genes have been isolated in plants, but little has been reported of FKBP genes in maize. In this study, a drought-induced FKBP gene, ZmFKBP20-1, was isolated from maize and was characterized for its role in stress responses using gene expression, protein subcellular localization, transformation in Arabidopsis, expression patterns of the stress-responsive genes, and physiological parameter analysis. During drought and salt stresses, ZmFKBP20-1 transgenic Arabidopsis plants exhibited enhanced tolerance, which was concomitant with the altered expression of stress/ABA-responsive genes, such as COR15a, COR47, ERD10, RD22, KIN1, ABI1, and ABI2. The resistance characteristics of ZmFKBP20-1 overexpression were associated with a significant increase in survival rate. These results suggested that ZmFKBP20-1 plays a positive role in drought and salt stress responses in Arabidopsis and provided new insights into the mechanisms of FKBP in response to abiotic stresses in plants.     

Overexpression of the ABC transporter gene <Emphasis Type="Italic">TsABCG11</Emphasis> increases cuticle lipids and abiotic stress tolerance in <Emphasis Type="Italic">Arabidopsis</Emphasis>

The cuticle, composed primarily of wax and cutin, covers most plant aerial surfaces and plays a vital role in interactions between plants and their environment. Some ATP-binding cassette G subfamily (ABCG) members are involved in cuticular lipid molecule exportation to outside in the plant surface. Thellungiella salsugineum, a relative of Arabidopsis thaliana with a heavy cuticle, has extreme stress tolerance. TsABCG11, an ABCG transporter was cloned (GenBank accession number JQ389853), and its structure was studied. qRT-PCR showed that TsABCG11 expression varied in different organs of T. salsugineum and was upregulated under ABA, NaCl, drought and cold conditions. The rosette leaves from 4-week-old TsABCG11 overexpressed (OE) Arabidopsis plants displayed lower rates of water loss and decreased chlorophyll-extracted rates compared to wild-type plants. TsABCG11-OE plants also exhibited significantly increased total cuticular wax and cutin monomer amounts, mainly due to prominent changes in the C₂₉, C₃₁, and C₃₃ alkanes in the wax and C18:2 dioic in cutin monomers, respectively. TsABCG11-OE seedlings exhibit lower root growth inhibition under 100 mM of NaCl or 1 µM of ABA than the wild type. Four-week-old TsABCG11-OE plants exhibited higher photosynthetic rates and water-use efficiency under cold stress (4 °C) than control plants. These results indicate that TsABCG11 plays an important role in cuticle lipid exportation and is involved in abiotic stresses, probably having a close relationship with extreme stress tolerance in T. salsugineum.     

A PCR-based analysis of plant DNA reveals the feeding preferences of <Emphasis Type="Italic">Apolygus lucorum</Emphasis> (Heteroptera: Miridae)

The mirid bug Apolygus lucorum (Meyer-Dür) (Heteroptera: Miridae) is a severe pest of cotton and other crops in China. The feeding preferences of this pest are unclear due to its frequent movement among different host plants and the inconspicuous signs of its feeding. Here, we present results of a field trial that used direct observation of bug densities and a PCR-based molecular detection assay to detect plant DNA in bugs to explore relationships between A. lucorum population abundance and its feeding preference between two host plants, Humulus scandens (Loureiro) Merrill and Medicago sativa L. The field-plot samples showed that A. lucorum adults generally prefer flowering host plants. Its density was significantly higher on flowering H. scandens than on seedlings of M. sativa, and a similarly higher bug density was observed on flowering M. sativa than on seedlings of H. scandens. In the laboratory, we designed two pairs of species-specific primers targeting the trnL-F region for H. scandens and M. sativa, respectively. The detectability of plant DNA generally decreased with time post-feeding, and the half-life of plant DNA detection (DS₅₀) in the gut was estimated as 6.26 h for H. scandens and 3.79 h for M. sativa with significant differences between each other. In mirid bugs exposed to seedlings of H. scandens and flowering M. sativa, the detection rate of M. sativa DNA was significantly higher than that of H. scandens. Meanwhile, in mirid bugs exposed to seedlings of M. sativa and flowering H. scandens, a significantly higher detection rate of H. scandens DNA was found. We developed a useful tool to detect the remaining plant food species specifically from the gut of A. lucorum in the current study. We provided direct evidence of its feeding preference between H. scandens and M. sativa at different growth stages, which strongly supported a positive correlation between population abundance and feeding preference of A. lucorum on different plants under field conditions. The findings provide new insights into the understanding of A. lucorum’s feeding preference, and are helpful for developing the strategies to control this pest.     

Engineering gibberellin metabolism in <Emphasis Type="Italic">Solanum nigrum</Emphasis> L. by ectopic expression of gibberellin oxidase genes

Gibberellins (GAs) control many aspects of plant development, including seed germination, shoot growth, flower induction and growth and fruit expansion. Leaf explants of Solanum nigrum (Black Nightshade; Solanaceae) were used for Agrobacterium-mediated delivery of GA-biosynthetic genes to determine the influence of their encoded enzymes on the production of bioactive GAs and plant stature in this species. Constructs were prepared containing the neomycin phosphotransferase (nptII) gene for kanamycin resistance as a selectable marker, and the GA-biosynthetic genes, their expression under the control of the CaMV 35S promoter. The GA-biosynthetic genes comprised AtGA20ox1, isolated from Arabidopsis thaliana, the product from which catalyses the formation of C₁₉-GAs, and MmGA3ox1 and MmGA3ox2, isolated from Marah macrocarpus, which encode functionally different GA 3-oxidases that convert C₁₉-GAs to biologically active forms. Increase in stature was observed in plants transformed with AtGA20ox1, MmGA3ox2 and MmGA3ox1 + MmGA3ox2, their presence and expression being confirmed by PCR and RT-PCR, respectively, accompanied by an increase in GA₁ content. Interestingly, MmGA3ox1 alone did not induce a sustained increase in plant height, probably because of only a marginal increase in bioactive GA₁ content in the transformed plants. The results are discussed in the context of regulating plant stature, since this strategy would decrease the use of chemicals to promote plant growth.