Activation of plant defense responses and sugar efflux by expression of pyruvate decarboxylase in potato leaves

Abstract

SummaryWhen plants are infected with avirulent pathogens, a selected group of plant cells rapidly die in a process commonly called the hypersensitive response (HR). Some mutations and overexpression of some unrelated genes mimic the HR lesion and associated defense responses. In all of these situations, a genetically programmed cell death pathway is activated wherein the cell actively participates in killing itself. Here we report a developmentally and environmentally regulated HR-like cell death in potato leaves constitutively expressing bacterial pyruvate decarboxylase (PDC). Lesions first appeared on the tip of fully expanded source leaves. Lesion formation was accompanied by activation of multiple defense responses and resulted in a significant resistance to Phytophthora infestans. The transgenic plants showed a five-to 12-fold increase in leaf tissue acetaldehyde and exported two-to 10-fold higher amounts of sucrose compared to the wildtype. When plants were grown at a higher temperature, both the lesion phenotype and sucrose export were restored to wild-type situations. The reduced levels of acetaldehyde at the elevated temperature suggested that the interplay of acetaldehyde with environmental and physiological factors is the inducer of lesion development. We propose that sugar metabolism plays a crucial role in the execution of cell death programs in plants.

Alleviation of low temperature sweetening in potato by expressing Arabidopsis pyruvate decarboxylase gene and stress-inducible rd29A: A preliminary study

“…An average yield of 1.005 kg/plant was obtained from control and L1 plant whereas L2 was affected by pests and yielded only 314.7 g/plant. It has been reported that transgenic potatoes constitutively overexpressing bacterial PDC showed lesion mimic phenotype in the leaves accompanied by induction of the plant defense response and resistance to Phytophthora infestans (Tadege et al 1998). In their study, the plant defense response was observed only at 18°C and not at 25°C and the extent of lesion phenotype was related to the level of PDC expression.…”

Carbon isotope analysis of acetaldehyde emitted from leaves following mechanical stress and anoxia

“…Although its metabolic origin remains uncertain, acetaldehyde is emitted into the atmosphere from plants after a wide variety of stresses and may play important roles in plant defence against stress. Acetaldehyde is a potent antibiotic and its emission from damaged tissue may help prevent infections (Utama et al 2002) and activate the expression of plant defence genes (Tadege et al 1998). Enhanced acetaldehyde emissions have been observed following mechanical wounding, desiccation, freeze-thaw events, herbivore attack, ozone fumigation, high light, high temperature, and many other biotic and abiotic stresses (Kimmerer & Kozlowski 1982;de Gouw et al 1999;Fall et al 1999;Karl et al 2001aKarl et al ,b, 2005Cojocariu et al 2005;Loreto et al 2006).…”

A New Subfamily of Sucrose Transporters, SUT4, with Low Affinity/High Capacity Localized in Enucleate Sieve Elements of Plants

“…Because of variability in the rate of photosynthesis according to changes in environmental conditions, and because sink demands change depending on development and external factors, we can reasonably assume that the rate of phloem loading of sucrose is regulated. In fact, the phenotype of transgenic plants overexpressing pyruvate decarboxylase indicates that sugar export from potato leaves can be upregulated by as much as 10-fold (Tadege et al, 1998). The increase in sucrose transport activity caused by modification of a conserved histidine in the first external loop (Lu and Bush, 1998) indicates that sucrose transporters may be directly regulated at the protein level.…”