Bridging the Gap: Type III Secretion Systems in Plant-Beneficial Bacteria

Type III secretion systems (T3SSs) are bacterial membrane-embedded nanomachines translocating effector proteins into the cytoplasm of eukaryotic cells. They have been intensively studied for their important roles in animal and plant bacterial diseases. Over the past two decades, genome sequencing has unveiled their ubiquitous distribution in many taxa of Gram-negative bacteria, including plant-beneficial ones. Here, we discuss the distribution and functions of the T3SS in two agronomically important bacterial groups: the symbiotic nodule-forming nitrogen-fixing rhizobia and the free-living plant-beneficial Pseudomonas spp. In legume-rhizobia symbiosis, T3SSs and their cognate effectors play important roles, including the modulation of the plant immune response and the initiation of the nodulation process in some cases. In plant-beneficial Pseudomonas spp., the roles of T3SSs are not fully understood, but pertain to plant immunity suppression, biocontrol against eukaryotic plant pathogens, mycorrhization facilitation, and possibly resistance against protist predation. The diversity of T3SSs in plant-beneficial bacteria points to their important roles in multifarious interkingdom interactions in the rhizosphere. We argue that the gap in research on T3SSs in plant-beneficial bacteria must be bridged to better understand bacteria/eukaryotes rhizosphere interactions and to support the development of efficient plant-growth promoting microbial inoculants.

Clohesyomyces symbioticus sp. nov., a fungal endophyte associated with roots of water smartweed (Persicaria amphibia)

The widespread aquatic plant Persicaria amphibia (water smartweed, Polygonaceae) occurs in both flooded aquatic habitats and moist terrestrial environments. Its physiological versatility and wide geographic range highlight its resilience to stress and make the species intriguing for the study of fungal endophytes. Endophytes occur within living plant tissues and are known from diverse aquatic, marine, and terrestrial plants, where they often mitigate plant responses to stress. As part of a study evaluating endophyte communities associated with aquatic plants in lentic waters of Arizona, USA, we isolated a distinctive clade of endophytes from healthy, living roots of seasonally inundated P. amphibia, which we describe here on the basis of morphology and evidence from four loci as new species Clohesyomyces symbioticus (Lindgomycetaceae, Pleosporales, Dothideomycetes, Ascomycota). Clohesyomyces has long been considered a monotypic genus comprising the saprobic species C. aquaticus, presently known from submerged wood in freshwater systems in Asia and Australia. Description of Clohesyomyces symbioticus highlights the occurrence of endophytism in this genus and expands its geographic scope to the western hemisphere.

Clathrin-mediated Endocytosis Facilitates Internalization of Magnaporthe oryzae Effectors into Rice Cells

Many filamentous eukaryotic plant pathogens, such as fungi and oomycetes, deliver effectors into living plant cells to suppress defenses and control plant processes needed for infection. To date, little is known about the mechanism by which these pathogens translocate effector proteins across the plasma membrane into the plant cytoplasm. The blast fungus Magnaporthe oryzae secretes cytoplasmic effectors into a specialized biotrophic interfacial complex (BIC) before translocation. Here we show that cytoplasmic effectors within BICs are packaged into dynamic vesicles that can occasionally be found separated from BICs in the host cytoplasm. Live cell imaging with fluorescently-labelled rice lines, showed that BICs are enriched in plant plasma membrane, actin, and Clathrin Light Chain-1, a marker for clathrin-mediated endocytosis (CME). We report that a novel cytoplasmic effector, Bas83, labels empty membrane vesicles surrounding BICs. Inhibition of CME using VIGS and chemical treatments results in a distinctive swollen BIC phenotype lacking effector vesicles. In contrast, fluorescent marker co-localization, VIGS and chemical inhibitor studies failed to implicate clathrin-independent endocytosis in effector vesicle formation. Taken together, this study provides evidence that cytoplasmic effector translocation is mediated by clathrin-mediated endocytosis in BICs and suggests a role for M. oryzae effectors in co-opting plant endocytosis.

Community Analysis of Culturable Sapwood Endophytes from Apulian Olive Varieties with Different Susceptibility to Xylella fastidiosa

Endophytes are symptomless fungal and/or bacterial microorganisms found in almost all living plant species. The symbiotic association with their host plants by colonizing the internal tissues has endowed them as a valuable tool to suppress diseases, stimulate growth, and promote stress resistance. In this context, the study of culturable endophytes residing the sapwood of Apulian olives might be a promising control strategy for xylem colonizing pathogens as Xylella fastidiosa. To date, olive sapwood cultivable endophytes are still under exploration; therefore, this work pursues a study of cultivable endophytes occurrence variation in the sapwood of different olive varieties under the effect of seasonality, geographical coordinates, and X. fastidiosa infection status. Our study confirms the stability of sapwood endophytic culturable communities in the resistant olive variety and presents the seasonal and geographical fluctuation of olive trees’ sapwood endophytes. It also describes the diversity and occurrence frequency of fungal and bacterial genera, and finally retrieves some of the sapwood-inhabiting fungal and bacterial isolates, known as biocontrol agents of plant pathogens. Thus, the potential role of these bacterial and fungal isolates in conferring olive tree protection against X. fastidiosa should be further investigated.

RoPod, a customizable toolkit for non-invasive root imaging, reveals cell type-specific dynamics of plant autophagy

Autophagy is the major catabolic process in eukaryotes and a key regulator of plant fitness. It enables rapid response to stress stimuli, essential for plastic adaptation of plants to changes in the environment. Fluorescent reporters and confocal microscopy are among the most frequently used methods for assessing plant autophagic activity. However, detection of dynamic changes in the pathway activity has been hampered by stresses imposed on living plant tissues during sample mounting and imaging. Here we implemented RoPod, a toolkit optimized for minimally-invasive time-lapse imaging of Arabidopsis roots, to reveal a time-resolved response of plant autophagy to drug treatments typically used for pathway modulation and discovered previously overlooked cell type-specific changes in the pathway response. These results not only give an insight into the complex dynamics of plant autophagy, but also provide necessary information for choosing sampling time for the end-point assays currently employed in plant autophagy research. RoPods are inexpensive and easy-to-use devices that are based on commercial or custom designed chambers, compatible with inverted microscopes. We describe a detailed protocol for the fabrication and use of RoPods and provide a complete pipeline including semi-automated image analysis for root hair growth assays, demonstrating the broader applicability of the RoPod toolkit.

Antioxidant Phenylpropanoid Glycosides from Ginkgo biloba Fruit and Identification of a New Phenylpropanoid Glycoside, Ginkgopanoside

Ginkgo biloba (Ginkgoaceae), well-known as the oldest living plant species and often referred to as a “living fossil,” is a famous medicinal plant that has been used in multiple countries to improve numerous illnesses, including anxiety, dementia, peripheral artery disease, and eye problems. We conducted a phytochemical exploration of G. biloba fruit, commonly consumed as a functional food as part of an ongoing natural product chemical research for the discovery of bioactive phytochemicals with novel structures. The natural product chemical analysis of the methanol extract of G. biloba fruit using column chromatography and high-performance liquid chromatography separation under the guidance of a liquid chromatography–mass spectrometry (LC/MS)-based analysis identified six phenylpropanoid glycosides (1–6), including one new compound, ginkgopanoside (1). The structures of the isolated compounds were elucidated by nuclear magnetic resonance spectroscopic data and LC/MS analysis, and the absolute configuration of compound 1 was established by chemical reactions followed by the application of Snatzke’s method. The 2,2-diphenyl-1-picrylhydrazyl (DPPH) scavenging activities of the isolated compounds 1–6 and the aglycone 1a of 1 were evaluated, and we found that compounds 1–5 exhibited antioxidant activities with IC50 values in the range 32.75–48.20 μM, while the aglycone 1a exhibited greater radical scavenging activity (IC50 = 5.23 μM) comparable to that of ascorbic acid (IC50 = 2.54 μM), a positive control, implying that the present of glucose may decrease the DPPH scavenging activity. These findings provide experimental information that the active phenylpropanoid glycosides could represent natural antioxidants for use in pharmaceuticals and functional foods.

Microbial Retting of Banana Pseudostem

Fibrous wastes correspond to approximately 54.3 wt.-% of a banana plant. The waste weight is mainly of bunches, stems, and leaves. These ligno-cellulosic fibre waste can be designed and tailored to yield value added products which can be exploited by the farmers, exporters and weavers. Pectin (plant cement) and hemicelluloses (22-25%) found in plant cell walls in the plate (middle lamella). These macromolecules have needs to be hydrolyzed faster without affecting the quality of fibre. The chemical and mechanical processes adopted for fibres actually affect color uptake, strength of fibre thus fetching lower price. We report a biological ecofriendly method of retting where pectinases produced by the endophytic microorganisms of banana pseudostem were used to separate the fibre bundles of cellulose.. Endophytes are microorganisms which live in close relationship with living plant tissues in a cooperative relationship delivering a few auxiliary metabolites and proteins with the possibility to hydrolyse a few plant-determined macromolecules of the host. They spend the entire or part of their lifecycle colonizing within sound tissues of the host plants.The endophytic pectinase helps to break down the cell walls and can find commercial application in extraction of fibres.Seven bacterial isolates were screened and isolated in pectinase screening agar medium [PSAM]. Pectinase producing endophytic bacteria is isolated from corm of Amorphophallus paeoniifolius reported by us are Staphylococcus sciuri, Exiguobacterium acetylicum, Exiguobacterium indicum which are good pectinase producers having specific activity of 8.26, 12.61, 6.81 respectively. Treatment of banana pseudostem with these microbes showed 91%, 94%, 96.7% loss in the total weight of stem leaving behind pure cellulose fibres.

Estimasi Karbon Tersimpan pada Nekromassa Tumbuhan di Rawa Lebak Kecamatan Martapura, Kalimantan Selatan

South Kalimantan is one of carbon contributor with an area of swamp with ± 1,140,207 ha area of swamp land. The potential area for changed to be an agricultural land is ± 763,207 ha, and the remain used for pool when the rainy season is come. The highest C reserve is in biomass (mass of living-plant part) and necromass (mass of dead-plant part) at the top soil, microbe, and soil-organic matter. Based on description above, the problem is how much stored-carbon in necromass of plant at martapura lowland swamp, because the largest carbon storage found in necromass of plant. The purpose of this study was to estimate the stored carbon contained in necromass of vegetation in lowland swamp. This research has been done in Martapura from April to July 2009. Sampling is done at 4 location include Tungkaran village, Keramat Baru village, Sungai Rangas village and Sungai Tabuk village. Each sampling location divided into 2 stations in one sampling. Analysis of stored-carbon in necromass of plant is using Walkey and Black Method. The result showed that average ranges of carbon stored in plant necromass are 490,95 – 1744,66 gm-2.