SANT proteins modulate gene expression by coordinating histone H3KAc and Khib levels and regulate plant heat tolerance.

Histone post-translational modifications (PTMs), such as acetylation and recently identified lysine 2-hydroxyisobutyrylation (Khib), act as active epigenomic marks in plants. SANT domain-containing proteins SANT1, SANT2, SANT3 and SANT4 (SANT1/2/3/4), derived from PIF/Harbinger transposases, form a complex with HISTONE DEACETYLASE 6 (HDA6) to regulate gene expression via histone deacetylation. However, whether SANT1/2/3/4 coordinate different types of PTMs to regulate transcription and mediate responses to specific stresses in plants remains unclear. Here, in addition to modulating histone deacetylation, we found that SANT1/2/3/4 proteins acted like HDA6 or HDA9 in regulating the removal of histone Khib in Arabidopsis (Arabidopsis thaliana). Histone H3 lysine acetylation (H3KAc) and histone Khib were coordinated by SANT1/2/3/4 to regulate gene expression, with H3KAc playing a predominant role and Khib acting complementarily to H3KAc. SANT1/2/3/4 mutation significantly increased the expression of heat-inducible genes with concurrent change of H3KAc levels under normal and heat stress conditions, resulting in enhanced thermotolerance. This study revealed the critical roles of Harbinger transposon-derived SANT domain-containing proteins in transcriptional regulation by coordinating different types of histone PTMs and in the regulation of plant thermotolerance by mediating histone acetylation modification.

Identification of natural allelic variation in TTL1 controlling thermotolerance and grain size by a rice super pan-genome.

Continuously increasing global temperatures present great challenges to food security. Grain size, one of the critical components determining grain yield in rice (Oryza sativa L.), is a prime target for genetic breeding. Thus, there is an immediate need for genetic improvement in rice to maintain grain yield under heat stress. However, quantitative trait loci (QTLs) endowing heat stress tolerance and grain size in rice are extremely rare. Here, we identified a novel negative regulator with pleiotropic effects, Thermo-Tolerance and grain Length 1 (TTL1), from the super pan-genomic and transcriptomic data. Loss-of-function mutations in TTL1 enhanced heat tolerance, and caused an increase in grain size by coordinating cell expansion and proliferation. TTL1 was shown to function as a transcriptional regulator and localized to the nucleus and cell membrane. Furthermore, haplotype analysis showed that hapL and hapS of TTL1 were obviously correlated with variations of thermotolerance and grain size in a core collection of cultivars. Genome evolution analysis of available rice germplasms suggested that TTL1 was selected during domestication of the indica and japonica rice subspecies, but still had much breeding potential for increasing grain length and thermotolerance. These findings provide insights into TTL1 as a novel potential target for the development of high-yield and thermotolerant rice varieties.

A domesticated Harbinger transposase forms a complex with HDA6 and promotes histone H3 deacetylation at genes but not TEs in Arabidopsis.

In eukaryotes, histone acetylation is a major modification on histone N-terminal tails that is tightly connected to transcriptional activation. HDA6 is a histone deacetylase involved in the transcriptional regulation of genes and transposable elements (TEs) in Arabidopsis thaliana. HDA6 has been shown to participate in several complexes in plants, including a conserved SIN3 complex. Here, we uncover a novel protein complex containing HDA6, several Harbinger transposon-derived proteins (HHP1, SANT1, SANT2, SANT3, and SANT4), and MBD domain-containing proteins (MBD1, MBD2, and MBD4). We show that mutations of all four SANT genes in the sant-null mutant cause increased expression of the flowering repressors FLC, MAF4, and MAF5, resulting in a late flowering phenotype. Transcriptome deep sequencing reveals that while the SANT proteins and HDA6 regulate the expression of largely overlapping sets of genes, TE silencing is unaffected in sant-null mutants. Our global histone H3 acetylation profiling shows that SANT proteins and HDA6 modulate gene expression through deacetylation. Collectively, our findings suggest that Harbinger transposon-derived SANT domain-containing proteins are required for histone deacetylation and flowering time control in plants.

Transcriptome Profile of Fusarium graminearum Treated by Putrescine.

Fusarium graminearum (F. graminearum) is the main pathogen of Fusarium head blight (FHB) in wheat, barley, and corn. Deoxynivalenol (DON), produced by F. graminearum, is the most prevalent toxin associated with FHB. The wheat defense compound putrescine can promote DON production during F. graminearum infection. However, the underlying mechanisms of putrescine-induced DON synthesis are not well-studied. To investigate the effect of putrescine on the global transcriptional regulation of F. graminearum, we treated F. graminearum with putrescine and performed RNA deep sequencing. We found that putrescine can largely affect the transcriptome of F. graminearum. Gene ontology (GO) and KEGG enrichment analysis revealed that having a large amount of DEGs was associated with ribosome biogenesis, carboxylic acid metabolism, glycolysis/gluconeogenesis, and amino acid metabolism pathways. Co-expression analysis showed that 327 genes had similar expression patterns to FgTRI genes and were assigned to the same module. In addition, three transcription factor genes were identified as hub genes in this module, indicating that they may play important roles in DON synthesis. These results provide important clues for further analysis of the molecular mechanisms of putrescine-induced DON synthesis and will facilitate the study of the pathogenic mechanisms of FHB.

Arbuscular mycorrhizal fungi enhance the copper tolerance of Tagetes patula through the sorption and barrier mechanisms of intraradical hyphae.

Arbuscular mycorrhizal fungi (AMF) are widespread soil fungi that can form endosymbiotic structures with the root systems of most plants and can improve the tolerance of host plants to heavy metals. In the present study, we investigated the effects of AMF (Glomus coronatum) inoculation on the tolerance of Tagetes patula L. to Cu. Almost all of the non-mycorrhizal plants exposed to 100 µM Cu died after 3 d, whereas phytotoxicity was only observed in mycorrhizal plants that were exposed to Cu concentrations greater than 100 µM. Analysing the dynamic accumulation of Cu indicated that, after 7 d of Cu exposure, less Cu was absorbed or accumulated by mycorrhizal plants than by control plants, and significantly less Cu was translocated to the shoots. Meanwhile, analysing the root morphology, the integrity of the root plasma membranes, the photosynthesis rate, and the content of essential elements of plants growing in cultures with 50 µM Cu revealed that AMF inoculation markedly alleviated the toxic effects of Cu stress on root system activity, photosynthesis rate, and mineral nutrient accumulation. In addition, to understand the Cu allocation, an energy spectrum analysis of Cu content at the transverse section of root tips was conducted and subsequently provided direct evidence that intraradical hyphae at the root endodermis could selectively immobilise large amounts of Cu. Indeed, the sorption and barrier mechanisms of AMF hyphae reduce Cu toxicity in the roots of T. patula and eventually enhance the plants' Cu tolerance.

Correction: Arbuscular mycorrhizal fungi enhance the copper tolerance of Tagetes patula through the sorption and barrier mechanisms of intraradical hyphae.

Correction for 'Arbuscular mycorrhizal fungi enhance the copper tolerance of Tagetes patula through the sorption and barrier mechanisms of intraradical hyphae' by Xishi Zhou et al., Metallomics, 2017, DOI: .

Cyanide removal by Chinese vegetation--quantification of the Michaelis-Menten kinetics.

BACKGROUND: Little is known about metabolism rates of environmental chemicals by vegetation. A good model compound to study the variation of rates among plant species is cyanide. Vascular plants possess an enzyme system that detoxifies cyanide by converting it to the amino acid asparagine. Knowledge of the kinetic parameters, the half-saturation constant (Km) and the maximum metabolic capacity (vmax), is very useful for enzyme characterization and biochemical purposes. The goal of this study is to find the enzyme kinetics (K(M) and vmax) during cyanide metabolism in the presence of Chinese vegetation, to provide quantitative data for engineered phytoremediation, and to investigate the variation of metabolic rates of plants. METHODS: Detached leaves (1.0 g fresh weight) from 12 species out of 9 families were kept in glass vessels with 100 mL of aqueous solution spiked with potassium cyanide at 23 degrees C for 28 h. Four different treatment concentrations of cyanide were used, ranging from 0.44 to 7.69 mg CN/L. The disappearance of cyanide from the aqueous solution was analyzed spectrophotometrically. Realistic values of the half-saturation constant (KM) and the maximum metabolic capacity (vmax) were estimated by a computer program using non-linear regression treatments. As a comparison, Lineweaver-Burk plots were also used to estimate the kinetic parameters. RESULTS AND DISCUSSION: The values obtained for K(M) and vmax varied with plant species. Using non-linear regression treatments, values of vmax and K(M) were found in a range between 6.68 and 21.91 mg CN/kg/h and 0.90 to 3.15 mg CN/L, respectively. The highest vmax was by Chinese elder (Sambucus chinensis), followed by upright hedge-parsley (Torilis japonica). The lowest Vmax was demonstrated by the hybrid willow (Salix matssudana x alba). However, the highest K(M) was found in the water lily (Nymphea teragona), followed by the poplar (Populus deltoides Marsh). The lowest K(M) was demonstrated by corn (Zea mays L.). The values of vmax were normally distributed with a mean of 13 mg CN/kg/h. CONCLUSIONS: Significant removal of cyanide from aqueous solution was observed in the presence of plant materials without phytotoxicity, even at high doses of cyanide. This gives rise to the conclusion that the Chinese plant species used in this study are all able to efficiently metabolize cyanide, although with different maximum metabolic capacities. A second conclusion is that the variation of metabolism rates between species is small. All these plants had a similar K(M), indicating the same enzyme is active in all plants. RECOMMENDATIONS AND OUTLOOK: Detoxification of cyanide with trees seems to be a feasible option for cleaning soils and water contaminated with cyanide. For phytoremediation projects, screening appropriate plant species adapted to local conditions should be seriously considered. More chemicals should be investigated to find common principles of the metabolism of environmental chemicals by plants.

Differences in Copper Absorption and Accumulation between Copper-Exclusion and Copper-Enrichment Plants: A Comparison of Structure and Physiological Responses.

Differences in copper (Cu) absorption and transport, physiological responses and structural characteristics between two types of Cu-resistant plants, Oenothera glazioviana (Cu-exclusion type) and Elsholtzia haichowensis (Cu-enrichment type), were investigated in the present study. The results indicated the following: (1) After 50 µM Cu treatment, the Cu ratio in the xylem vessels of E. haichowensis increased by 60%. A Cu adsorption experiment indicated that O. glazioviana exhibited greater resistance to Cu, and Cu absorption and the shoot/root ratio of Cu were significantly lower in O. glazioviana than in E. haichowensis. (2) An analysis of the endogenous abscisic acid (ABA) variance and exogenous ABA treatment demonstrated that the ABA levels of both plants did not differ; exogenous ABA treatment clearly reduced Cu accumulation in both plants. (3) The leaf stomatal density of O. glazioviana was significantly less than that of E. haichowensis. Guard cells in E. haichowensis plants were covered with a thick cuticle layer, the epidermal hair was more numerous and longer, and the number of xylem conduits in the root was small. (4) The transpiration rate and the stomatal conductance of O. glazioviana were both significantly lower than those of E. haichowensis, regardless of whether the plants were treated with Cu. Taken together, these results indicate that the differences in the structural characteristics between these two plant species, particularly in the characteristics related to plant transpiration, are important factors that govern whether plants acquire or exclude Cu.

Metabolism of cyanide by Chinese vegetation.

Cyanide is a high-volume production chemical and the most commonly used leaching reagent for gold and silver extraction. Its environmental behavior and fate is of significant concern because it is a highly toxic compound. Vascular plants possess an enzyme system that detoxifies cyanide by converting it to the amino acid asparagine. This paper presents an investigation of the potential of Chinese vegetation to degrade cyanide. Detached leaves (1.5 g fresh weight) from 28 species of 23 families were kept in glass vessel with 100 ml of aqueous solution spiked with potassium cyanide at 23.5 degrees C for 28 h. Cyanide concentrations ranged from 0.83 to 1.0 CN mg l(-1). The disappearance of cyanide from the aqueous solution was analyzed spectrophotometrically. The fastest cyanide removal was by Chinese elder, Sambucus chinensis, with a removal capacity of 8.8 mg CN kg(-1) h(-1), followed by upright hedge-parsley (Torilis japonica) with a value of 7.5 mg CN kg(-1) h(-1). The lowest removal capacity had the snow-pine tree (Credrus deodara (Roxb.) Loud). Results from this investigation indicated that a wide range of plant species is able to efficiently metabolize cyanide. Therefore, cyanide elimination with plants seems to be a feasible option for cleaning soils and water contaminated by cyanide from gold and silver mines or from other sources.