Improvement of drought tolerance in maize: towards the functional validation of the Zm-Asr1 gene and increase of water use efficiency by over-expressing C4-PEPC.

Water availability is one of the major limiting factors for plant growth. Maize is particularly sensitive to water stress at reproductive stages with a strong impairment of photosynthesis and grain filling. Here, we describe the use of genetic transformation first to assess the role of a candidate gene Asr1-a putative transcription factor-as an explanation for genetically linked drought tolerance Quantitative Trait Loci (QTLs), and second to modify CO(2) fixation rates in leaves through changes of C(4) phosphoenolpyruvate carboxylase (C(4)-PEPC) activity. Transgenic Asr1 over-expressing lines show an increase in foliar senescence under drought conditions. The highest C(4)-PEPC overexpressing line exhibited an increase (+30%) in intrinsic water use efficiency (WUE) accompanied by a dry weight increase (+20%) under moderate drought conditions. Opposite effects were observed for transgenic plants under-expressing the corresponding proteins. The data presented here indicate the feasibility to increase the level of endogenous biochemical activities related to water economy and/or drought tolerance, and opens a way to develop maize varieties more tolerant to dry growing conditions.

Field tolerance to fungal pathogens of Brassica napus constitutively expressing a chimeric chitinase gene.

Constitutive overexpression of a protein involved in plant defense mechanisms to disease is one of the strategies proposed to increase plant tolerance to fungal pathogens. A hybrid endochitinase gene under a constitutive promoter was introduced by Agrobacterium-mediated transformation into a winter-type oilseed rape (Brassica napus var. oleifera) inbred line. Progeny from transformed plants was challenged using three different fungal pathogens (Cylindrosporium concentricum, Phoma lingam, Sclerotinia sclerotiorum) in field trials at two different geographical locations. These plants exhibited an increased tolerance to disease as compared with the nontransgenic parental plants.

Structural organization of str 246C and str 246N, plant defense-related genes from Nicotiana tabacum.

We have previously identified a cDNA clone, pNt246, whose corresponding transcripts accumulate in leaves in response to inoculation by compatible and incompatible isolates of the phytopathogenic bacterium Pseudomonas solanacearum [19]. We now describe the nucleotide sequence of a genomic clone, str 246C, corresponding to this cDNA species, and of a related genomic clone, str 246N, which appears to be a pseudogene with a 5'-end deletion. The nucleotide sequence of the str 246C gene was found to be identical to that of the parA gene, previously shown to be regulated by auxin [28, 29]. Upstream of the str 246N gene, sequences homologous to a Bam HI repetitive element described in Vicia faba [15] are present within an ORF showing significant homologies to an integrase-encoding gene of several retroviruses. This observation indicates that this highly repetitive DNA originates from sequences present in transposable mobile elements.

Chitin oligosaccharides as elicitors of chitinase activity in melon plants.

Chitin oligosaccharides elicited chitinase activity in melon plants. Hexamer to nonamer were the most efficient elicitors: hexamer for maximal stimulation of colorimetrically assessed chitinase activity, heptamer for maximal stimulation of radiochemically assessed chitinase activity. Chitinase elicitation was a rapid response to these elicitors: it occurred within 6 hours after treatment and was maximal at 12-24 hours. In addition, chitinase induction in melon plants by these oligosaccharides was both local and systemic.

Cell Surfaces in Plant-Microorganism Interactions : VI. Elicitors of Ethylene from Colletotrichum lagenarium Trigger Chitinase Activity in Melon Plants.

Treatment of melon leaves or seedlings with elicitors of Colletotrichum lagenarium, a fungal pathogen of melon, increases chitinase activity. In treated leaves, chitinase is enhanced within the first 6 hours and becomes 2 to 10 times higher than in control leaves after 24 hours. Ethylene is increased simultaneously and is correlated with chitinase elicitation. In the presence of aminoethoxyvinylglycine, an inhibitor of ethylene synthesis, both elicitor-induced ethylene and elicitor-induced chitinase are inhibited. This inhibition is overcome by added exogenous ethylene. On the other hand, 1-aminocyclopropane-1-carboxylic acid the direct precursor of ethylene, triggers chitinase activity. Chitinase elicitation is thought to be a protein synthesis dependent process, as it does not occur in the presence of cycloheximide.

Cell surfaces in plant-microorganism interactions : v. Elicitors of fungal and of plant origin trigger the synthesis of ethylene and of cell wall hydroxyproline-rich glycoprotein in plants.

Treatment of melon hypocotyls or petioles with an elicitor from Colletotrichum lagenarium, a fungal pathogen of melons, causes an initial transitory inhibition of protein synthesis and, after 18 hours, induces the synthesis of a plant cell wall hydroxyproline-rich glycoprotein (HRGP). Microgram amounts of elicitor are sufficient for maximum elicitation of HRGP when the elicitor is injected into hypocotyls. High elicitor concentrations have a strong inhibitory effect on total protein synthesis. Ethylene is increased early in elicitor-treated plant material, and may be involved in HRGP elicitation. In the presence of aminoethoxyvinylglycine, an inhibitor of ethylene synthesis, both elicitor-induced ethylene and elicitor-induced HRGP are inhibited. On the other hand, 1-aminocyclopropane-1-carboxylic acid, the direct precursor of ethylene, triggers the synthesis of HRGP to the same extent as the elicitor of C. lagenarium, and partly restores in elicitor-treated petioles the synthesis of ethylene and of HRGP after previous inhibition by aminoethoxyvinylglycine. Elicitation of HRGP occurs in other systems, such as soybeans when inoculated with an elicitor from Phytophtora megasperma f. sp. glycinea, and when melons are incubated with an elicitor isolated from their cell walls.

Cell Surfaces in Plant-Microorganism Interactions : IV. Fungal Glycopeptides Which Elicit the Synthesis of Ethylene in Plants.

The production of ethylene by melon (Cucumis melo cv Cantaloup charentais) tissues is stimulated during incubation in the presence of fungal glycopeptides extracted from Colletotrichum lagenarium, a pathogen of melon. These glycopeptides, called elicitors of ethylene, are found in the mycelium, the cell wall, and the culture filtrate. Elicitation of ethylene is a relatively early phenomenon and lasts for several hours. Upon purification of the crude elicitor extract by gel filtration and ion exchange chromatography, three elicitors were isolated. The three elicitors contained amino acid, sugar, and phosphate residues, and they have a decreased activity after partial chemical degradation of their sugar moiety.Elicitation of ethylene is not fungal species specific. Elicitors of phytoalexins, obtained from three Phytophtora species, enhanced ethylene biosynthesis in melon tissues.

Cell Surfaces in Plant-Microorganism Interactions : III. In Vivo Effect of Ethylene on Hydroxyproline-Rich Glycoprotein Accumulation in the Cell Wall of Diseased Plants.

Ethylene production and cell wall hydroxyproline-rich glycoprotein (HRGP) biosynthesis are greatly enhanced in melon (Cucumin melo cv. Cantaloup charentais) seedlings infected with Colletotrichum lagenarium. Short-term experiments performed in the presence of specific inhibitors of the ethylene pathway from methionine, namely l-canaline and amino-ethoxyvinylglycine, indicate that under non-toxic conditions, both ethylene and [(14)C]hydroxyproline deposition in the cell wall of infected tissues are significantly lowered. On the contrary, treatment of healthy tissues with 1-aminocyclopropane 1-carboxylic acid, a natural precursor of ethylene, stimulates both the production of the hormone and the incorporation of [(14)C]hydroxyproline into cell wall proteins.The data provide the first evidence of the in vivo effect of ethylene on the cell wall hydroxyproline-rich glycoprotein biosynthesis in plants.

Cell Surfaces in Plant-Microorganism Interactions: II. Evidence for the Accumulation of Hydroxyproline-rich Glycoproteins in the Cell Wall of Diseased Plants as a Defense Mechanism.

Enrichment of the cell wall in hydroxyproline-rich glycoprotein is involved in the defense of muskmelon (Cucumis melo) seedlings to Colletotrichum lagenarium, the causative agent of anthracnose. The extent to which this accumulation proceeds may be experimentally modified by treating plants with ethylene or growing them in the presence of free l-trans-hydroxyproline. It appears that the increase in the wall hydroxyproline-rich glycoprotein mediated through ethylene is paralleled by an increasing resistance of the host to the pathogen. Inversely, inhibiting the synthesis of this glycoprotein in diseased plants is strictly correlated to an accelerated and more intense colonization of the host by the pathogen.In both cases, the inverse relationship between the accumulation of hydroxyproline-rich glycoproteins and the ability of the pathogen to develop in the host has been checked by the quantification, in infected tissues, of glucosamine, a characteristic component of chitin-containing fungi.