Summary
Phosphite (Phi) is used commercially to manage diseases mainly caused by oomycetes, primarily due to its low cost compared with other fungicides and its persistent control of oomycetous ...pathogens. We explored the use of Phi in controlling the fungal pathogens Puccinia emaculata and Phakopsora pachyrhizi, the causal agents of switchgrass rust and Asian soybean rust, respectively. Phi primes host defenses and efficiently inhibits the growth of P. emaculata, P. pachyrhizi and several other fungal pathogens tested. To understand these Phi‐mediated effects, a detailed molecular analysis was undertaken in both the host and the pathogen. Transcriptomic studies in switchgrass revealed that Phi activates plant defense signaling as early as 1 h after application by increasing the expression of several cytoplasmic and membrane receptor‐like kinases and defense‐related genes within 24 h of application. Unlike in oomycetes, RNA sequencing of P. emaculata and P. pachyrhizi did not exhibit Phi‐mediated retardation of cell wall biosynthesis. The genes with reduced expression in either or both rust fungi belonged to functional categories such as ribosomal protein, actin, RNA‐dependent RNA polymerase, and aldehyde dehydrogenase. A few P. emaculata genes that had reduced expression upon Phi treatment were further characterized. Application of double‐stranded RNAs specific to P. emaculata genes encoding glutamate N‐acetyltransferase and cystathionine gamma‐synthase to switchgrass leaves resulted in reduced disease severity upon P. emaculata inoculation, suggesting their role in pathogen survival and/or pathogenesis.
Significance Statement
Phosphite (Phi) is an important low‐input chemical used against oomycete pathogens, and understanding its mode of action against fungal pathogens will have great implications for the development of novel fungicides. To achieve this, first the role of Phi in controlling rust pathogens was studied, secondly Phi‐mediated transcriptional alterations taking place in both host and pathogen were monitored, and finally several Phi‐targeted rust genes were validated by spraying plants with corresponding double‐stranded RNAs.
The channeling of metabolites is an essential step of metabolic regulation in all living organisms. Multifunctional enzymes with defined domains for metabolite compartmentalization are rare, but in ...many cases, larger assemblies forming multimeric protein complexes operate in defined metabolic shunts. In
, a multimeric complex was discovered that contains a 13-lipoxygenase and allene oxide synthase (AOS) as well as allene oxide cyclase. All three plant enzymes are localized in chloroplasts, contributing to the biosynthesis of jasmonic acid (JA). JA and its derivatives act as ubiquitous plant defense regulators in responses to both biotic and abiotic stresses. AOS belongs to the superfamily of cytochrome P450 enzymes and is named CYP74A. Another CYP450 in chloroplasts, hydroperoxide lyase (HPL, CYP74B), competes with AOS for the common substrate. The products of the HPL reaction are green leaf volatiles that are involved in the deterrence of insect pests. Both enzymes represent non-canonical CYP450 family members, as they do not depend on O
and NADPH-dependent CYP450 reductase activities. AOS and HPL activities are crucial for plants to respond to different biotic foes. In this mini-review, we aim to summarize how plants make use of the LOX2-AOS-AOC2 complex in chloroplasts to boost JA biosynthesis over volatile production and how this situation may change in plant communities during mass ingestion by insect pests.
Grain development is one of the biological processes, which contributes to the final grain yield. To understand the molecular changes taking place during the early grain development, we profiled ...proteomes of two common wheat cultivars P271 and Chinese Spring (CS) with large and small grains, respectively at three grain developmental stages (4, 8, and 12 days post anthesis). An iTRAQ (isobaric tags for relative and absolute quantitation) based proteomics approach was used for this purpose. More than 3,600 proteins were reported to accumulate during early grain development in both wheat cultivars. Of these 3,600 proteins, 130 expressed differentially between two wheat cultivars, and 306 exhibited developmental stage-specific accumulation in either or both genotypes. Detailed bioinformatic analyses of differentially expressed proteins (DEPs) from the large- and small-grain wheat cultivars underscored the developmental differences observed between them and shed light on the molecular and cellular processes contributing to these differences.
localization of either or both sets of DEPs to wheat chromosomes exhibited a biased genomic distribution with chromosome 4D contributing largely to it. These results corresponded well with the earlier studies, performed in common wheat, where chromosome 4D was reported to harbor QTLs for yield contributing traits specifically grain length. Collectively, our results provide insight into the molecular processes taking place during early grain development, a knowledge, which may prove useful in improving wheat grain yield in the future.
DNA methylation is sensitive and responsive to stressful environmental conditions. Nonetheless, the extent to which condition-induced somatic methylation modifications can impose transgenerational ...effects remains to be fully understood. Even less is known about the biological relevance of the induced epigenetic changes for potentially altered well-being of the organismal progenies regarding adaptation to the specific condition their progenitors experienced.
We analyzed DNA methylation pattern by gel-blotting at genomic loci representing transposable elements and protein-coding genes in leaf-tissue of heavy metal-treated rice (Oryza sativa) plants (S0), and its three successive organismal generations. We assessed expression of putative genes involved in establishing and/or maintaining DNA methylation patterns by reverse transcription (RT)-PCR. We measured growth of the stressed plants and their unstressed progenies vs. the control plants. We found (1) relative to control, DNA methylation patterns were modified in leaf-tissue of the immediately treated plants, and the modifications were exclusively confined to CHG hypomethylation; (2) the CHG-demethylated states were heritable via both maternal and paternal germline, albeit often accompanying further hypomethylation; (3) altered expression of genes encoding for DNA methyltransferases, DNA glycosylase and SWI/SNF chromatin remodeling factor (DDM1) were induced by the stress; (4) progenies of the stressed plants exhibited enhanced tolerance to the same stress their progenitor experienced, and this transgenerational inheritance of the effect of condition accompanying heritability of modified methylation patterns.
Our findings suggest that stressful environmental condition can produce transgenerational epigenetic modifications. Progenies of stressed plants may develop enhanced adaptability to the condition, and this acquired trait is inheritable and accord with transmission of the epigenetic modifications. We suggest that environmental induction of heritable modifications in DNA methylation provides a plausible molecular underpinning for the still contentious paradigm of inheritance of acquired traits originally put forward by Jean-Baptiste Lamarck more than 200 years ago.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Hexaploid bread wheat (Triticum aestivum L., genome BBAADD) is generally more salt tolerant than its tetraploid wheat progenitor (Triticum turgidum L.). However, little is known about the ...physiological basis of this trait or about the relative contributions of allohexaploidization and subsequent evolutionary genetic changes on the trait development. Here, we compared the salt tolerance of a synthetic allohexaploid wheat (neo-6 x) with its tetraploid (T. turgidum ; BBAA) and diploid (Aegilops tauschii; DD) parents, as well as a natural hexaploid bread wheat (nat-6 x). We studied 92 morphophysiological traits and analyzed homeologous gene expression of a major salt-tolerance gene High-Affinity K ⁺ Transporter 1;5 (HKT1;5). We observed that under salt stress, neo-6 x exhibited higher fitness than both of its parental genotypes due to inheritance of favorable traits like higher germination rate from the 4 x parent and the stronger root Na ⁺ retention capacity from the 2 x parent. Moreover, expression of the D-subgenome HKT1;5 homeolog, which is responsible for Na ⁺ removal from the xylem vessels, showed an immediate transcriptional reprogramming following allohexaploidization, i.e., from constitutive high basal expression in Ae. tauschii (2 x) to salt-induced expression in neo-6 x . This phenomenon was also witnessed in the nat-6 x . An integrated analysis of 92 traits showed that, under salt-stress conditions, neo-6 x resembled more closely the 2 x than the 4 x parent, suggesting that the salt stress induces enhanced expressivity of the D-subgenome homeologs in the synthetic hexaploid wheat. Collectively, the results suggest that condition-dependent functionalization of the subgenomes might have contributed to the wide-ranging adaptability of natural hexaploid wheat.
Cytosine methylation at CG sites (ᵐCG) plays critical roles in development, epigenetic inheritance, and genome stability in mammals and plants. In the dicot model plant Arabidopsis thaliana , ...methyltransferase 1 (MET1), a principal CG methylase, functions to maintain ᵐCG during DNA replication, with its null mutation resulting in global hypomethylation and pleiotropic developmental defects. Null mutation of a critical CG methylase has not been characterized at a whole-genome level in other higher eukaryotes, leaving the generality of the Arabidopsis findings largely speculative. Rice is a model plant of monocots, to which many of our important crops belong. Here we have characterized a null mutant of OsMet1-2 , the major CG methylase in rice. We found that seeds homozygous for OsMet1-2 gene mutation (OsMET1-2 ⁻/⁻), which directly segregated from normal heterozygote plants (OsMET1-2 ⁺/⁻), were seriously maldeveloped, and all germinated seedlings underwent swift necrotic death. Compared with wild type, genome-wide loss of ᵐCG occurred in the mutant methylome, which was accompanied by a plethora of quantitative molecular phenotypes including dysregulated expression of diverse protein-coding genes, activation and repression of transposable elements, and altered small RNA profiles. Our results have revealed conservation but also distinct functional differences in CG methylases between rice and Arabidopsis .
Allopolyploidization has been a driving force in plant evolution. Formation of common wheat (Triticum aestivum L.) represents a classic example of successful speciation via allopolyploidy. ...Nevertheless, the immediate chromosomal consequences of allopolyploidization in wheat remain largely unexplored. We report here an in-depth investigation on transgenerational chromosomal variation in resynthesized allohexaploid wheats that are identical in genome constitution to common wheat. We deployed sequential FISH, genomic in situ hybridization (GISH), and homeolog-specific pyrosequencing, which enabled unequivocal identification of each of the 21 homologous chromosome pairs in each of >1,000 individual plants from 16 independent lines. We report that whole-chromosome aneuploidy occurred ubiquitously in early generations (from selfed generation S ₁ to >S ₂₀) of wheat allohexaploidy although at highly variable frequencies (20–100%). In contrast, other types of gross structural variations were scant. Aneuploidy included an unexpected hidden type, which had a euploid chromosome number of 2 n = 42 but with simultaneous loss and gain of nonhomeologous chromosomes. Of the three constituent subgenomes, B showed the most lability for aneuploidy, followed by A, but the recently added D subgenome was largely stable in most of the studied lines. Chromosome loss and gain were also unequal across the 21 homologous chromosome pairs. Pedigree analysis showed no evidence for progressive karyotype stabilization even with multigenerational selection for euploidy. Profiling of two traits directly related to reproductive fitness showed that although pollen viability was generally reduced by aneuploidy, the adverse effect of aneuploidy on seed-set is dependent on both aneuploidy type and synthetic line.
Thioredoxins (Trxs) are ubiquitous small proteins with a redox-active disulfide bridge. In their reduced form, they constitute very efficient protein disulfide oxidoreductases. In chloroplasts, two ...types of Trxs (f and m) coexist and play central roles in the regulation of the Calvin cycle and other processes. Here, we identified a class of Trx targets in the inner plastid envelope membrane of chloroplasts that share a CxxC motif almost equal to73 aa from their carboxyl-terminal end. Members of this group belong to a superfamily of Rieske iron-sulfur proteins involved in protein translocation and chlorophyll metabolism. These proteins include the protein translocon protein TIC55, the precursor NADPH:protochlorophyllide oxidoreductase translocon protein PTC52, which operates as protochlorophyllide a-oxygenase, and the lethal leaf spot protein LLS1, which is identical with pheophorbide a oxygenase. The role of these proteins in dark/light regulation and oxidative control by the Trx system is discussed.
Disease resistance strategies are powerful approaches to sustainable agriculture because they reduce chemical input into the environment. Recently, Piriformospora indica, a plant-root-colonizing ...basidiomycete fungus, has been discovered in the Indian Thar desert and was shown to provide strong growth-promoting activity during its symbiosis with a broad spectrum of plants Verma, S. et al. (1998) Mycologia 90, 896-903. Here, we report on the potential of P. indica to induce resistance to fungal diseases and tolerance to salt stress in the monocotyledonous plant barley. The beneficial effect on the defense status is detected in distal leaves, demonstrating a systemic induction of resistance by a root-endophytic fungus. The systemically altered "defense readiness" is associated with an elevated antioxidative capacity due to an activation of the glutathione-ascorbate cycle and results in an overall increase in grain yield. Because P. indica can be easily propagated in the absence of a host plant, we conclude that the fungus could be exploited to increase disease resistance and yield in crop plants.
The barley (Hordeum vulgare L.) mutants fch2 and clo-f2 comprise an allelic group of 14 Chl b-deficient lines. The genetic map position of fch2 corresponds to the physical map position of the gene ...encoding chlorophyllide a oxygenase. This enzyme converts chlorophyllide a to chlorophyllide b and it is essential for Chl b biosynthesis. The fch2 and clo-f2 barley lines were shown to be mutated in the gene for chlorophyllide a oxygenase. A five-base insertion was found in fch2 and base deletions in clo-f2.101, clo-f2.105, clo-f2.2800 and clo-f2.3613. In clo-f2.105 and clo-f2.108, nonsense base exchanges were discovered. All of these mutations led to a premature stop of translation and none of the mutants formed Chl b. The mutant clo-f2.2807 was transcript deficient and formed no Chl b. Missense mutations in clo-f2.102 (leading to the amino acid exchange D495N) and clo-f2.103 (G280D) resulted in a total lack of Chl b, whereas in the missense mutants clo-f2.107 (P419L), clo-f2.109 (A94T), clo-f2.122 (C320Y), clo-f2.123 (A94T), clo-f2.133 (A376V) and clo-f2.181 (L373F) intermediate contents of Chl b were determined. The missense mutations affect conserved residues, and their effect on chlorophyllide a oxygenase is discussed. The mutations in clo-f2.102, clo-f2.103, clo-f2.133 and clo-f2.181 may influence electron transfer as illustrated in the active site of a structural model protein. The changes in clo-f2.107, clo-f2.109, clo-f2.122 and clo-f2.123 may lead to Chlb deficiency by interfering with the regulation of chlorophyllide a oxygenase. The correlation of mutations and phenotypes strongly supports that the barley locus fch2 encodes chlorophyllide a oxygenase.
PDF
