Diverse range of gene activity during arabidopsis thaliana leaf senescence includes pathogen-independent induction of defense-related genes

To determine the range of gene activities associated with leaf senescence, we have identified genes that show preferential transcript accumulation during this developmental stage. The mRNA levels of a diverse array of gene products increases during leaf senescence, including a protease, a ribosomal protein, two cinnamyl alcohol dehydrogenases, a nitrilase and glyoxalase II. Two of the genes identified are known to be pathogen-induced. The senescence specificity of each gene was determined by characterization of transcript accumulation during leaf development and in different tissues. The increased expression of nitrilase in senescent leaves is paralleled by an increase in free indole-3-acetic acid (IAA) levels. Additionally, we have demonstrated that the induction of defense-related genes during leaf senescence is pathogen-independent and that salicylic acid accumulation is not essential for this induction. Our data indicate that the induction of certain genes involved in plant defense responses is a component of the leaf senescence program

Heterologous expression and characterization of a putative glycoside hydrolase family 43 arabinofuranosidase from Clostridium thermocellum B8

An extensive list of putative cellulosomal enzymes from C. thermocellum is now available in the public databanks, however, most of these remain unvalidated with regard to their activity and expression control mechanisms. This is particularly true of those enzymes putatively involved in hemicellulose deconstruction. Our research group has been working on mapping and characterization of glycoside hydrolases produced by C. thermocellum B8, that are critical for lignocellulosic biomass deconstruction. One of the identified genes expressed during growth on sugar cane bagasse and straw is axb8, which encodes a putative cellulosomal GH43_29 α-arabinofuranosidase (EC 3.2.1.55) that has not previously been characterized at the molecular or kinetic levels. The AxB8 predicted amino acid sequence presented GH43 and dockerin domains, as well as a family 6 carbohydrate-binding module (CBM6). Also, it is a close homologue of Firmicutes putatives α-arabinofuranosidases, including cellulosomal proteins. Multiple alignment analysis grouped AxB8 in a cluster with four uncharacterized putative GH43_29 subfamily enzymes, all containing dockerin type I domain and CBM6 modules. Purified heterologously expressed AxB8 showed activity against the synthetic substrates pNPX (p-nytrophenyl-β-D-xylopyranoside) and pNPA (p-nytrophenyl-α-L-arabinofuranoside), as well as against the natural substrate wheat arabinoxylan (WAX), with maximal activity at 50 °C and pH between 5.0 and 6.0. The WAX degradation profile by AxB8 is different from those typically seen for α-arabinofuranosidases, presenting mainly xylose as a hydrolysis product, instead of arabinose. In addition, unlike other GH43_29 enzymes already characterized, AxB8 did not present activity against arabinan. Kinetic parameters using pNPA as a substrate were Km of 23 ± 3 mM and kcat of 104 ± 7 s−1. Despite its activity against pNPX, we did not observe AxB8 saturation with this substrate. AxB8 is the first member in its clade to be characterized regarding kinetic parameters, and together with its closest homologues could represent a large group of glycoside hydrolases with particular properties within the GH43_29 subfamily

Diversity of soil fungal communities of Cerrado and its closely surrounding agriculture Welds

Cerrado is a savanna-like region that covers a large area of Brazil. Despite its biological importance, the Cerrado has been the focus of few microbial diversity studies. A molecular approach was chosen to characterize the soil fungal communities in four areas of the Cerrado biome: a native Cerrado, a riverbank forest, an area converted to a soybean plantation, and an area converted to pasture. Global diversity of fungal communities in each area was assessed through Ribosomal intergenic spacer analysis which revealed remarkable diVerences among the areas studied. Sequencing of approximately 200 clones containing 18S rDNA sequences from each library was performed and, according to the genetic distance between sequences, these were assigned to operational taxonomic units (OTUs). A total of 75, 85, 85, and 70 OTUs were identiWed for the native Cerrado, riverbank forest, pasture, and soybean plantation, respectively. Analysis of sequences using a similarity cutoV value of 1% showed that the number of OTUs for the native Cerrado area was reduced by 35%; for the soybean plantation, a reduction by more than 50% was observed, indicating a reduction in fungal biodiversity associated with anthropogenic activity. This is the Wrst studydemonstrating the anthropogenic impact on Cerrado soil fungal diversity

Identification of fungal OTUs sequences shared by groups of oil palm leaf samples affected by FY in disease stages 2, 5 and 8, but not present in asymptomatic leaves.

<p>Identification of fungal OTUs sequences shared by groups of oil palm leaf samples affected by FY in disease stages 2, 5 and 8, but not present in asymptomatic leaves.</p

Fungal diversity in oil palm leaves showing symptoms of Fatal Yellowing disease

<div><p>Oil palm (<i>Elaeis guineensis</i> Jacq.) is an excellent source of vegetable oil for biodiesel production; however, there are still some limitations for its cultivation in Brazil such as Fatal Yellowing (FY) disease. FY has been studied for many years, but its causal agent has never been determined. In Colombia and nearby countries, it was reported that the causal agent of Fatal Yellowing (<i>Pudrición del Cogollo</i>) is the oomycete <i>Phytophthora palmivora</i>, however, several authors claim that Fatal Yellowing and <i>Pudrición del Cogollo</i> (PC) are different diseases. The major aims of this work were to test, using molecular biology tools, Brazilian oil palm trees for the co-occurrence of the oomycete <i>Phytophthora</i> and FY symptoms, and to characterize the fungal diversity in FY diseased and healthy leaves by next generation sequencing. Investigation with specific primers for the genus <i>Phytophthora</i> showed amplification in only one of the samples. Analysis of the fungal ITS region demonstrated that, at the genus level, different groups predominated in all symptomatic samples, while <i>Pyrenochaetopsis</i> and unclassified fungi predominated in all asymptomatic samples. Our results show that fungal communities were not the same between samples at the same stage of the disease or among all the symptomatic samples. This is the first study that describes the evolution of the microbial community in the course of plant disease and also the first work to use high throughput next generation sequencing to evaluate the fungal community associated with leaves of oil palm trees with and without symptoms of FY.</p></div

Sequence abundance at different taxonomic levels.

<p>Relative abundance of fungal sequences at phyla (A) and class (B) levels in oil palm leaves of plants with (stages 2, 5 and 8) or without Fatal Yellowing based on ITS region sequences. AP—FY <u>A</u>symptomatic <u>P</u>lants; SP—FY <u>S</u>ymptomatic <u>P</u>lants.</p

Identification of fungal OTUs sequences shared by groups of oil palm leaf samples affected by FY in disease stages 2, 5 and 8, but not present in asymptomatic leaves.

<p>Identification of fungal OTUs sequences shared by groups of oil palm leaf samples affected by FY in disease stages 2, 5 and 8, but not present in asymptomatic leaves.</p