Cell Surfaces in Plant-Microorganism Interactions

Chitinase gene expression has been shown to be transcriptionally regulated by a number of inducers, including ethylene, elicitors, and pathogen attack. To investigate the mechanism(s) responsible for induction of chitinase gene expression in response to various stimuli, we have developed a transient gene expression system in bean (Phaseolus vulgaris) protoplasts that is responsive to ethylene and elicitor treatment. This system was used to study the expression of a chimeric gene composed of the 5' flanking sequences of a bean endochitinase gene fused to the reporter gene ,-glucuronidase linked to a 3' fragment from nopaline synthase. Addition of 1-aminocyclopropane-1-carboxylic acid, the direct precursor of ethylene, or elicitors such as chitin oligosaccharides or cell wall fragments derived from Colletotrichum lagenarium, to transformed protoplasts resulted in a rapid and marked increase in the expression of the chimeric gene. The kinetics and dose response for these treatments were similar to those observed for the native gene in vivo. Analyses of 5' deletion mutants in the protoplast system indicated that DNA sequences located between -305 and -236 are important for both ethylene and elicitor induction of the reporter gene.Chitinase, a lytic enzyme found in most higher plants (1, 3), catalyzes the hydrolysis of chitin, a A-( 1,4)-linked polymer of 2-acetamido-2-deoxy-13-D-glucose. Although no endogenous substrate for this enzyme has been found in plants, chitin is a major component of the cell walls of many fungi (31). For this reason, Abeles et al. (1) proposed that chitinase functions as a defense against chitin-containing pathogens. This hypothesis is supported by studies which indicate that chitinase levels are increased in response to pathogen attack (19,20,24,25). In vitro studies have demonstrated further that plant chitinases are capable of hydrolyzing the cell walls ofplant pathogenic fungi (30) and releasing elicitors ofdefense reactions (14). In addition, plants treated with the phytohormone ethylene (1, 3) or elicitors such as isolated fungal cell walls (7,21,22), endogenous plant cell walls (21), or chitin oligosaccharides (14, 23), have also been shown to contain

Section: Elicitor and Acc Treatment Of Plantsmentioning

confidence: 99%

Regulation of a Chitinase Gene Promoter by Ethylene and Elicitors in Bean Protoplasts

Roby

Broglie²,

Gaynor³

et al. 1991

“…In contrast, untreated Petunia corollas were sensitive to exogenous ethylene (Table V). As IAA is not the inducing substance in Petunia either (7), we suggest that elicitors of the kind observed after mechanical perturbation (18) or fungal infection (9,19) are produced by stigmas upon wounding or pollination, and lead to the production of the mobile wilting factor ACC in the lower parts of the style.…”

mentioning

confidence: 99%

Lack of Control by Early Pistillate Ethylene of the Accelerated Wilting of Petunia hybrida Flowers

Hoekstra

Weges²

1986

Well before pollen tube penetration, ethylene has begun to disseminate from pollinated styles of Petunia hybrida flowers. Previous stigmatic application of aminoethoxyvinylglycine (AVG) completely prevented this ethylene synthesis, indicating that the endogenous 1-aminocyclopropane-1-carboxylic acid (ACC) in pollen is not readily converted on the stigma. Compared to other flower parts, the capacity of the ethylene forming enzyme was largest in the stigma. When applied to the stigma, ACC caused ethylene synthesis, but did not accelerate wilting, unless high concentrations (20 nanomols) were used. Upon pollination or stigma wounding, the early ethylene evolved exclusively from the gynoecium, much later followed by the synthesis of corolla ethylene. Employing wideneck Erlenmeyer flasks, the competitive inhibitor of ethylene action, norbornadiene, was applied to entire flowers in situ, with delaying effects on wound-induced wilting. In contrast, norbornadiene treatment of styles alone, using capillaries, could not postpone wilting. Pollination with foreign pollen species did not lead to accelerated corolla wilting, notwithstanding considerable synthesis of ethylene during the frst 5 hours. In situ treatment of the stigma with AVG considerably delayed wound-and pollination-induced wilting. Removal of the entire AVG-treated style 6 hours after stigma wounding still allowed for the postponement of the accelerated wilting, even at very low concentrations of AVG. It is concluded that early stylar ethylene does not play a role in the acceleration of wilting but that, much later, corolla ethylene does, induced by a mobile wilting factor from the stigma, which is ACC. levels ofthe immediate precursor, ACC' (24). The sequential rise in ACC content of carnation stigmas, ovaries, receptacles, and petals upon pollination strongly suggests that ACC might be the mobile wilting stimulus (12). Pollen itself might be the trigger in this respect as it sometimes contains large amounts of ACC (F.

“…Ethylene biosynthesis, one common response of plant tissues to pathogen attack (21), is stimulated by a variety of plant-and pathogen-derived polysaccharides and proteins (4,26,28). Ethylene has been suggested to play a role in activating certain defense responses in some plant tissues (9).…”

Section: Introductionmentioning

confidence: 99%

Ethylene Biosynthesis-Inducing Xylanase

Dean¹,

Anderson²

1991

The ethylene biosynthesis-inducing endoxylanase (EIX) from xylan-induced cultures of the fungus, Trichoderma viride, was purified to near homogeneity and compared with the EIX isolated from Cellulysin. Both enzymes migrate as 9.2 kilodalton proteins during gel filtration chromatography under nondenaturing conditions, but the mature polypeptide migrates as a 22 kilodalton band in sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The amino acid composition of the 22 kilodalton polypeptide is enriched by Gly, Ser, Thr, Trp, and Tyr, but depleted in Ala, Glx, Leu, and Lys. Both proteins lack sulfur-containing amino acids. The protein is glycosylated, and inhibition of EIX synthesis by tunicamycin suggests that at least some of the sugar moieties are linked to asparagine residues. EIX appears to be synthesized initially as a 25 kilodalton precursor protein that is processed to 22 kilodalton during secretion.A factor limiting our understanding of plant defense responses in plant-pathogen interactions has been the paucity of elicitors which have been purified and structurally characterized. Ethylene biosynthesis, one common response of plant tissues to pathogen attack (21), is stimulated by a variety of plant-and pathogen-derived polysaccharides and proteins (4,26,28). Ethylene has been suggested to play a role in activating certain defense responses in some plant tissues (9). This laboratory has previously demonstrated that an endo-B-1,4-xylanase (1,4-f3-D-xylan xylanohydrolase; EC 3.2.1.8) purified from a commercial mixture of fungal enzymes, Cellulysin3, is a potent elicitor ofethylene biosynthesis in tobacco (Nicotiana tabacum L. cv Xanthi) ( 1,12).