The dual nature of trehalose in citrus canker disease: a virulence factor for Xanthomonas citri subsp. citri and a trigger for plant defence responses.

Xanthomonas citri subsp. citri (Xcc) is a bacterial pathogen that causes citrus canker in susceptible Citrus spp. The Xcc genome contains genes encoding enzymes from three separate pathways of trehalose biosynthesis. Expression of genes encoding trehalose-6-phosphate synthase (otsA) and trehalose phosphatase (otsB) was highly induced during canker development, suggesting that the two-step pathway of trehalose biosynthesis via trehalose-6-phosphate has a function in pathogenesis. This pathway was eliminated from the bacterium by deletion of the otsA gene. The resulting XccΔotsA mutant produced less trehalose than the wild-type strain, was less resistant to salt and oxidative stresses, and was less able to colonize plant tissues. Gene expression and proteomic analyses of infected leaves showed that infection with XccΔotsA triggered only weak defence responses in the plant compared with infection with Xcc, and had less impact on the host plant's metabolism than the wild-type strain. These results suggested that trehalose of bacterial origin, synthesized via the otsA-otsB pathway, in Xcc, plays a role in modifying the host plant's metabolism to its own advantage but is also perceived by the plant as a sign of pathogen attack. Thus, trehalose biosynthesis has both positive and negative consequences for Xcc. On the one hand, it enables this bacterial pathogen to survive in the inhospitable environment of the leaf surface before infection and exploit the host plant's resources after infection, but on the other hand, it is a tell-tale sign of the pathogen's presence that triggers the plant to defend itself against infection.

Trehalose metabolism: from osmoprotection to signaling.

Trehalose is a non-reducing disaccharide formed by two glucose molecules. It is widely distributed in Nature and has been isolated from certain species of bacteria, fungi, invertebrates and plants, which are capable of surviving in a dehydrated state for months or years and subsequently being revived after a few hours of being in contact with water. This disaccharide has many biotechnological applications, as its physicochemical properties allow it to be used to preserve foods, enzymes, vaccines, cells etc., in a dehydrated state at room temperature. One of the most striking findings a decade ago was the discovery of the genes involved in trehalose biosynthesis, present in a great number of organisms that do not accumulate trehalose to significant levels. In plants, this disaccharide has diverse functions and plays an essential role in various stages of development, for example in the formation of the embryo and in flowering. Trehalose also appears to be involved in the regulation of carbon metabolism and photosynthesis. Recently it has been discovered that this sugar plays an important role in plant-microorganism interactions.

The role of trehalose and its transporter in protection against reactive oxygen species.

During menadione stress, trehalose was necessary intracellularly, but under H2O2, the sugar was required on the outside of the plasma membrane. The mechanism of protection involves minimizing the oxidative damage caused to both proteins and lipids, which would require the presence of trehalose on both sides of the lipid bilayer.

Effect of hydrostatic pressure of a mutant of Saccharomyces cerevisiae deleted in the trehalose-6-phosphate synthase gene.

Mutants Saccharomyces cerevisiae deleted on the trehalose-6-phosphate synthase gene (tps1) and their parental wild-type cells were submitted to hydrostatic pressure in the range of 0-200 MPa. Experimental evidence showed that viability for both strains decreased with increasing pressure and that tps1 mutants, unable to accumulate trehalose, were more sensitive to hydrostatic pressure than the wild-type cells. Additionally, both tps1 and wild-type cells in the stationary phase, when there is an accumulation of endogenous trehalose, were more resistant to pressure than proliferating cells. Under these conditions, mutant cells were also more sensitive to pressure treatment than the wild type. The present work also showed that mild pressure pretreatment did not induce hydrostatic pressure resistance (barotolerance) in yeast cells.

The role of trehalose in cell stress.

Water is usually thought to be required for the living state, but many organisms can withstand anhydrobiosis when essentially all of their body water has been removed. The mechanisms for survival to this kind of stress could be similar in microbes, plants and animals. One common feature is the accumulation of sugars by anhydrobiotic organisms. Trehalose, which is one of the most effective saccharides in preventing phase transition events in the lipid bilayer, is accumulated by anhydrobiotic organisms in large amounts. It lowers membrane phase transitions in dry yeast cells, thus preventing imbibitional damages when cells are rehydrated. Yeast cells have a trehalose carrier in the plasma membrane which endows them with the ability to protect both sides of the membrane. Kinetic analysis of the trehalose transport activity in Saccharomyces cerevisiae cells revealed the existence of a multicomponent system with a constitutive low-affinity uptake component and a high-affinity H(+)-trehalose symporter regulated by glucose repression.

The role of trehalose in cell stress

Water is usually thought to be required for the living state, but many organisms can withstand anhydrobiosis When essentially all of their body water has been removed. The mechanisms for survival to this Kind of stress could be similar in microbes, plants and animals. One common feature is the accumulation of sugars by anhydrobiotic organisms. Trehalose, which is one of the most effective saccharides in preventing phase transition events in the lipid bilayer, is accumulated by anhydrobiotic organisms in large amounts. It lowers membrane phase transitions in dry yeast cells, thus preventing imbibitional damages when cells are rehydrated. Yeast cells have a trehalose carrier in the plasma membrane which endows them with the ability to protect both sides of the membrane. Kinetic analysis of the trehalose transport activity in Saccharomyces cerevisiae cells revealed the exoistence of a multicomponent system with a constitutive low-affinity uptake component and a high-affinity H+ - trehalose symporter regulated by glucose repression.