Identification of the toxin components of Rhizoctonia solani AG1-IA and its destructive effect on plant cell membrane structure

Rice sheath blight is a fungal disease caused mainly by Rhizoctonia solani AG1-IA. Toxins are a major pathogenic factor of R. solani, and some studies have reported their toxin components; however, there is no unified conclusion. In this study, we reported the toxin components and their targets that play a role in R. solani AG1-IA. First, toxins produced by R. solani AG1-IA were examined. Several important phytotoxins, including benzoic acid (BZA), 5-hydroxymethyl-2-furanic aid (HFA), and catechol (CAT), were identified by comparative analysis of secondary metabolites from AG1-IA, AG1-IB, and healthy rice. Follow-up studies have shown that the toxin components of this fungus can rapidly disintegrate the biofilm structure while maintaining the content of host plant membrane components, thereby affecting the organelles, which may also explain the lack of varieties highly resistant to sheath blight

Quantitative Profiling of Arabidopsis Polar Glycerolipids under Two Types of Heat Stress

At the cellular level, the remodelling of membrane lipids and production of heat shock proteins are the two main strategies whereby plants survive heat stress. Although many studies related to glycerolipids and HSPs under heat stress have been reported separately, detailed alterations of glycerolipids and the role of HSPs in the alterations of glycerolipids still need to be revealed. In this study, we profiled the glycerolipids of wild-type Arabidopsis and its HSP101-deficient mutant hot-1 under two types of heat stress. Our results demonstrated that the alterations of glycerolipids were very similar in wild-type Arabidopsis and hot-1 during heat stress. Although heat acclimation led to a slight decrease of glycerolipids, the decrease of glycerolipids in plants without heat acclimation is more severe under heat shock. The contents of 36:x monogalactosyl diacylglycerol (MGDG) were slightly increased, whereas that of 34:6 MGDG and 34:4 phosphatidylglycerol (PG) were severely decreased during moderate heat stress. Our findings suggested that heat acclimation could reduce the degradation of glycerolipids under heat shock. Synthesis of glycerolipids through the prokaryotic pathway was severely suppressed, whereas that through the eukaryotic pathway was slightly enhanced during moderate heat stress. In addition, HSP101 has a minor effect on the alterations of glycerolipids under heat stress

Maintenance or Collapse: Responses of Extraplastidic Membrane Lipid Composition to Desiccation in the Resurrection Plant <i>Paraisometrum mileense</i>

<div><p>Resurrection plants usually grow in specific or extreme habitats and have the capacity to survive almost complete water loss. We characterized the physiological and biochemical responses of <i>Paraisometrum mileense</i> to extreme desiccation and found that it is a resurrection plant. We profiled the changes in lipid molecular species during dehydration and rehydration in <i>P. mileense</i>, and compared these with corresponding changes in the desiccation-sensitive plant <i>Arabidopsis thaliana</i>. One day of desiccation was lethal for <i>A. thaliana</i> but not for <i>P. mileense</i>. After desiccation and subsequent rewatering, <i>A. thaliana</i> showed dramatic lipid degradation accompanied by large increases in levels of phosphatidic acid (PA) and diacylglycerol (DAG). In contrast, desiccation and rewatering of <i>P. mileense</i> significantly decreased the level of monogalactosyldiacylglycerol and increased the unsaturation of membrane lipids, without changing the level of extraplastidic lipids. Lethal desiccation in <i>P. mileense</i> caused massive lipid degradation, whereas the PA content remained at a low level similar to that of fresh leaves. Neither damage nor repair processes, nor increases in PA, occurred during non-lethal desiccation in <i>P. mileense</i>. The activity of phospholipase D, the main source of PA, was much lower in <i>P. mileense</i> than in <i>A. thaliana</i> under control conditions, or after either dehydration or rehydration. It was demonstrated that low rates of phospholipase D-mediated PA formation in <i>P. mileense</i> might limit its ability to degrade lipids to PA, thereby maintaining membrane integrity following desiccation.</p></div

Amount of lipid in each head-group class and total polar lipid during dehydration (Deh) and rehydration (Reh) of <i>P. mileense</i> and <i>A. thaliana</i> leaves.

<p>The percentage relative change in lipids of dehydration RC (F–D) is the value for the difference between the values of Fresh and Deh discs, divided by the value of Fresh discs; that of rehydration RC (D–R) is the value for the significant difference between the values of Deh and Reh discs, divided by the value of Deh discs. Values in the same row with different letters are significantly different (<i>P</i><0.05). Values are means ± standard deviation (<i>n</i> = 4 or 5).</p

Transphosphatidylation activities of <i>A. thaliana</i> and <i>P. mileense</i>.

<p>Reaction products were separated by thin-layer chromatography and monitored by UV colorimetric analysis.</p

Hierarchical clustering analysis of lipid molecular species during dehydration (Deh) and rehydration (Reh) of <i>P. mileense</i> and <i>A. thaliana</i> leaves.

<p>(A) Contents (nmol/mg dry weight) of lipid molecular species. (B) Compositions (mol %) of lipid molecular species. The colored bar within a column represents the lipid molecular species in the corresponding plants and treatments. The color of each bar represents the abundance of the indicated lipid species, which is expressed relative to the change from the mean center of each lipid species within all treatments. Lipid species in the corresponding lipid classes were sorted using class (as indicated), total acyl carbons (within a class), and total double bonds (with class and total acyl carbons) in ascending order. Values are means (<i>n</i> = 4 or 5).</p

Half-lethal dehydration (Deh 4 d), lethal dehydration (Deh 5 d), and subsequent rehydration (Reh) of <i>P. mileense</i> leaves.

<p>White coloration (upper picture) or low <i>F_v</i>/<i>F_m</i> values for variable fluorescence (lower picture). The color bar at the bottom indicates <i>F_v</i>/<i>F_m</i> values.</p

Lipid content in each head-group class and total polar lipid during half-lethal (Deh 4 d) or lethal dehydration (Deh 5 d) and rehydration for one day after dehydration for five days (Reh) in <i>P. mileense</i> leaves.

<p>Values in the same row with different letters are significantly different (<i>P</i><0.05). Values are means ± standard deviation (<i>n</i> = 4 or 5).</p

Changes in (A) soluble sugar, (B) proline, (C) malondialdehyde (MDA), and (D) relative electricity conductivity during dehydration (Deh) and rehydration (Reh) in <i>P. mileense</i> and <i>A. thaliana</i> leaves.

<p>Values are means ± standard deviation (<i>n</i>  =  4 or 5). Values in the same bar type with different letters indicate that values are significantly different (<i>P</i> < 0.05). </p

Changes of pigments during dehydration (Deh) and rehydration (Reh) in <i>P. mileense</i> and <i>A. thaliana</i> leaves.

<p>Values in the same row with different letters are significantly different (<i>P</i><0.05). Values are means ± SD (<i>n</i> = 4 or 5).</p