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.     

The <Emphasis Type="Italic">ABI2</Emphasis>-dependent abscisic acid signalling controls HrpN-induced drought tolerance in <Emphasis Type="Italic">Arabidopsis</Emphasis>

HrpN, a protein produced by the plant pathogenic bacterium Erwinia amylovora, has been shown to stimulate plant growth and resistance to pathogens and insects. Here we report that HrpN activates abscisic acid (ABA) signalling to induce drought tolerance (DT) in Arabidopsis thaliana L. plants grown with water stress. Spraying wild-type plants with HrpN-promoted stomatal closure decreased leaf transpiration rate, increased moisture and proline levels in leaves, and alleviated extents of damage to cell membranes and plant drought symptoms caused by water deficiency. In plants treated with HrpN, ABA levels increased; expression of several ABA-signalling regulatory genes and the important effector gene rd29B was induced or enhanced. Induced expression of rd29B, promotion of stomatal closure, and reduction in drought severity were observed in the abi1-1 mutant, which has a defect in the phosphatase ABI1, after HrpN was applied. In contrast, HrpN failed to induce these responses in the abi2-1 mutant, which is impaired in the phosphatase ABI2. Inhibiting wild-type plants to synthesize ABA eliminated the role of HrpN in promoting stomatal closure and reducing drought severity. Moreover, resistance to Pseudomonas syringae developed in abi2-1 as in wild-type plants following treatment with HrpN. Thus, an ABI2-dependent ABA signalling pathway is responsible for the induction of DT but does not affect pathogen defence under the circumstances of this study.Hong-Ping Dong and Haiqin Yu contributed equally to this study and are regarded as joint first authors.     

Mutagens induced chromosomal damage in <Emphasis Type="Italic">Lablab purpureus</Emphasis> (L.) Sweet var. <Emphasis Type="Italic">typicus</Emphasis>

Cytological analysis with respect to meiotic behaviour is considered to be the one of the most dependable indices to estimate the potency of mutagens and to elucidate the response of various genotypes to a particular mutagen. Seeds of Lablab purpureus (L.) Sweet var. typicus cv. CO(Gb)14 were subjected to different doses/concentrations of gamma rays and EMS. The effects of different mutagenic treatments on meiosis were studied on treated and control plants. Various types of meiotic aberrations such as stickiness, clumping of chromosomes, laggards, ring chromosomes and precocious movements were observed in the mutagenic treatments. As increase in the concentration, the frequency of cells showing chromosomal aberrations shows a linear increase up to a certain level. However, the EMS treatments proved to be more effective in inducing meiotic aberrations as compared to gamma rays.     

A chalcone synthase gene <Emphasis Type="Italic">AeCHS</Emphasis> from <Emphasis Type="Italic">Abelmoschus esculentus</Emphasis> regulates flavonoid accumulation and abiotic stress tolerance in transgenic <Emphasis Type="Italic">Arabidopsis</Emphasis>

Chalcone synthase (CHS) is one of the key enzymes in flavonoid biosynthesis pathway in plants. However, the roles of AeCHS gene from Abelmoschus esculentus in flavonoid accumulation and tolerance to abiotic stresses have not been studied. In this study, the AeCHS gene was cloned from Abelmoschus esculentus. The open reading frame contained 1170 nucleotides encoding 389 amino acids. The coding region of AeCHS was cloned into a binary vector under the control of 35S promoter and then transformed into Arabidopsis to obtain transgenic plants. Overexpression of AeCHS increased the production of downstream flavonoids and the expression of related genes in the flavonoid biosynthesis pathway. It also improved resistance to salt and mannitol stresses during seed germination and root development. Further component and enzymatic analyses showed the decreased content of H₂O₂ and malondialdehyde and the increased activities of superoxide dismutase (SOD) and peroxidase (POD) in transgenic seedlings. Meanwhile, the expression level of AtSOD and AtPOD genes was up-regulated against salt and osmotic stresses. Together, our finding indicated that changing the expression level of AeCHS in plants alters the accumulation of flavonoids and regulates plantlet tolerance to abiotic stress by maintaining ROS homeostasis. The AeCHS gene has the potential to be used to increase the content of valuable flavonoids and improve the tolerance to abiotic stresses in plants.     

Increased tolerance to salt stress in the phosphate-accumulating <Emphasis Type="Italic">Arabidopsis</Emphasis> mutants <Emphasis Type="Italic">siz1</Emphasis> and <Emphasis Type="Italic">pho2</Emphasis>

High salinity is an environmental factor that inhibits plant growth and development, leading to large losses in crop yields. We report here that mutations in SIZ1 or PHO2, which cause more accumulation of phosphate compared with the wild type, enhance tolerance to salt stress. The siz1 and pho2 mutations reduce the uptake and accumulation of Na⁺. These mutations are also able to suppress the Na⁺ hypersensitivity of the sos3-1 mutant, and genetic analyses suggest that SIZ1 and SOS3 or PHO2 and SOS3 have an additive effect on the response to salt stress. Furthermore, the siz1 mutation cannot suppress the Li⁺ hypersensitivity of the sos3-1 mutant. These results indicate that the phosphate-accumulating mutants siz1 and pho2 reduce the uptake and accumulation of Na⁺, leading to enhanced salt tolerance, and that, genetically, SIZ1 and PHO2 are likely independent of SOS3-dependent salt signaling.     

Overexpression of wheat <Emphasis Type="Italic">TaNCED</Emphasis> gene in <Emphasis Type="Italic">Arabidopsis</Emphasis> enhances tolerance to drought stress and delays seed germination

Abscisic acid (ABA) regulates various plant physiological processes, especially participates in the plant responses to harsh environments. The 9-cis-epoxycarotenoid dioxygenase (NCED) is a key enzyme in ABA biosynthesis pathway. Here, a TaNCED with an 1 887-bp open reading frame was cloned from wheat, which encodes a peptide of 628 amino acids. A chloroplast transit peptide sequence was found at the N-terminus of the TaNCED protein. Multiple sequence alignments indicate that the TaNCED protein shared high similarities with other NCEDs from different species. Real-time quantitative PCR analysis shows that expression of TaNCED was strongly up-regulated by treatments with ABA, polyethylene glycol, and drought stress, and it was down-regulated during germination of the wheat seeds. Ectopic overexpression of the TaNCED gene in Arabidopsis resulted in an increase of endogenous ABA and free proline content. A lower water loss rate and stomatal conductance of leaves were found in the transgenic plants in comparison with the wild type. Subsequently, the transgenic plants displayed an enhanced tolerance to drought stress but delayed seed germination. These data provide evidence that the TaNCED might play a primary role in regulation of ABA content during water stress and seed dormancy.