Untitled

Abstract

Genes from the biocontrol fungus Trichoderma atroviride encoding the antifungal proteins endochitinase or exochitinase (N-acetyl-beta-D-hexosaminidase) were inserted into 'Marshall McIntosh' apple singly and in combination. The genes were driven by a modified CaMV35S promoter. The resulting plants were screened for resistance to Venturia inaequalis, the causal agent of apple scab, and for effects of enzyme expression on growth. Disease resistance was correlated with the level of expression of either enzyme when expressed alone but exochitinase was less effective than endochitinase. The level of expression of endochitinase was negatively correlated with plant growth while exochitinase had no consistent effect on this character. Plants expressing both enzymes simultaneously were more resistant than plants expressing either single enzyme at the same level; analyses indicated that the two enzymes acted synergistically to reduce disease. Selected lines, especially one expressing low levels of endochitinase activity and moderate levels of exochitinase activity, were highly resistant in growth chamber trials and had negligible reduction in vigor relative to control plants. We believe that this is the first report of resistance in plants induced by expression of an N-acetylhexosaminidase and is the first report of in planta synergy between an exochitinase and an endochitinase.

Expression of a Chitinase Gene from Metarhizium anisopliae in Tobacco Plants Confers Resistance against Rhizoctonia solani

“…Even though similar results have been obtained by Lorito et al [8] in tobacco, a negative correlation between the level of an endochitinase gene solely and endo-and exochitinase genes combined on growth of apple transgenic plants was registered in two previous papers by Bolar et al [10,11].…”

“…Lorito et al [8] reported the correct post-translation processing of secretion signal peptides belonging to chitinases from T. harzianum and tomato when expressed in tobacco plants. Conversely, Bolar et al [11] found an inefficient splicing in exochitinase transcripts from T. atroviride in apple plants.…”

“…A single endochitinase gene from Trichoderma harzianum confers enhanced resistance to pathogens including the Deuteromycetes Alternaria alternata, Alternaria solani, Botrytis cinerea (leaf spot and fruit rot; [8]), the Basidiomycete Rhizoctonia solani (attacks the stem and root of tobacco and potato plants; [8]), and the Ascomycete Venturia inaequalis (apple scab disease; [10,11]). The same gene was introduced into black spruce and hybrid poplar and conferred enhanced resistance to Melampsora medusae and Cylindrocladium floridanum, respectively [12].…”

Differential resistance of switchgrass Panicum virgatum L. lines to fall armyworms Spodoptera frugiperda (J. E. Smith)

“…Chitin-degrading enzymes such as chitinase and NAHA, both alone or in combination, can also confer resistance to insects (Lawrence and Novak 2006;Dowd et al 2007a) and plant pathogens (Bolar et al 2000(Bolar et al , 2001. Moreover, they can increase levels of disease resistance in maize and other plants when expressed transgenically ).…”

Recombinant DNA Technology in Apple

“…The authors hypothesized that pyramiding both genes, each with a relatively low level of expression, may lead to high resistance whilst retaining good vigor. Transgenic lines with both genes (low ech42 and high Nag 70 expression) had a high level of scab resistance without significant growth reduction [49]. The authors reported that selected lines were evaluated in the field for resistance, growth, and fruit quality; however, no data are currently published.…”