Signals and Their Perception for Remodelling, Adjustment and Repair of the Plant Cell Wall.

The integrity of the cell wall is important for plant cells. Mechanical or chemical distortions, tension, pH changes in the apoplast, disturbance of the ion homeostasis, leakage of cell compounds into the apoplastic space or breakdown of cell wall polysaccharides activate cellular responses which often occur via plasma membrane-localized receptors. Breakdown products of the cell wall polysaccharides function as damage-associated molecular patterns and derive from cellulose (cello-oligomers), hemicelluloses (mainly xyloglucans and mixed-linkage glucans as well as glucuronoarabinoglucans in Poaceae) and pectins (oligogalacturonides). In addition, several types of channels participate in mechanosensing and convert physical into chemical signals. To establish a proper response, the cell has to integrate information about apoplastic alterations and disturbance of its wall with cell-internal programs which require modifications in the wall architecture due to growth, differentiation or cell division. We summarize recent progress in pattern recognition receptors for plant-derived oligosaccharides, with a focus on malectin domain-containing receptor kinases and their crosstalk with other perception systems and intracellular signaling events.

Piriformospora indica promotes early flowering in Arabidopsis through regulation of the photoperiod and gibberellin pathways.

Flowering in plants is synchronized by both environmental cues and internal regulatory factors. Previous studies have shown that the endophytic fungus Piriformospora indica promotes the growth and early flowering in Coleus forskohlii (a medicinal plant) and Arabidopsis. To further dissect the impact of P. indica on pathways responsible for flowering time in Arabidopsis, we co-cultivated Arabidopsis with P. indica and used RT-qPCR to analyze the main gene regulation networks involved in flowering. Our results revealed that the symbiotic interaction of Arabidopsis with P. indica promotes early flower development and the number of siliques. In addition, expression of the core flowering regulatory gene FLOWERING LOCUS T (FT), of genes controlling the photoperiod [CRYPTOCHROMES (CRY1, CRY2) and PHYTOCHROME B (PHYB)] and those related to gibberellin (GA) functions (RGA1, AGL24, GA3, and MYB5) were induced by the fungus, while key genes controlling the age and autonomous pathways remained unchanged. Moreover, early flowering promotion conferred by P. indica was promoted by exogenous GA and inhabited by GA inhibitor, and this effect could be observed under long day and neutral day photoperiod. Therefore, our data suggested that P. indica promotes early flowering in Arabidopsis likely through photoperiod and GA rather than age or the autonomous pathway.

Root endophyte Piriformospora indica DSM 11827 alters plant morphology, enhances biomass and antioxidant activity of medicinal plant Bacopa monniera.

Unorganized collections and over exploitation of naturally occurring medicinal plant Bacopa monniera is leading to rapid depletion of germplasm and is posing a great threat to its survival in natural habitats. The species has already been listed in the list of highly threatened plants of India. This calls for micropropagation based multiplication of potential accessions and understanding of their mycorrhizal associations for obtaining plants with enhanced secondary metabolite contents. The co-cultivation of B. monniera with axenically cultivated root endophyte Piriformospora indica resulted in growth promotion, increase in bacoside content, antioxidant activity and nuclear hypertrophy of this medicinal plant.

The root endophyte fungus Piriformospora indica leads to early flowering, higher biomass and altered secondary metabolites of the medicinal plant, Coleus forskohlii.

This study was undertaken to investigate the influence of plant probiotic fungus Piriformospora indica on the medicinal plant C. forskohlii. Interaction of the C. forskohlii with the root endophyte P. indica under field conditions, results in an overall increase in aerial biomass, chlorophyll contents and phosphorus acquisition. The fungus also promoted inflorescence development, consequently the amount of p-cymene in the inflorescence increased. Growth of the root thickness was reduced in P. indica treated plants as they became fibrous, but developed more lateral roots. Because of the smaller root biomass, the content of forskolin was decreased. The symbiotic interaction of C. forskohlii with P. indica under field conditions promoted biomass production of the aerial parts of the plant including flower development. The plant aerial parts are important source of metabolites for medicinal application. Therefore we suggest that the use of the root endophyte fungus P. indica in sustainable agriculture will enhance the medicinally important chemical production.

Expression of BvGLP-1 encoding a germin-like protein from sugar beet in Arabidopsis thaliana leads to resistance against phytopathogenic fungi.

Nematode (Heterodera schachtii) resistance in sugar beet (Beta vulgaris) is controlled by a single dominant resistance gene, Hs1(pro-1). BvGLP-1 was cloned from resistant sugar beet. The BvGLP-1 messenger (m)RNA is highly upregulated in the resistant plants after nematode infection, suggesting its role in the Hs1(pro-1) mediated resistance. BvGLP-1 exhibits sequence homology to a set of plant germin-like proteins (GLP), from which several have proved to be functional in plant basal or defense resistance against fungal pathogens. To test whether BvGLP-1 is also involved in the plant-fungus interaction, we transferred BvGLP-1 into Arabidopsis and challenged the transgenic plants with the pathogenic fungi Verticillium longisporum and Rhizoctonia solani as well as with the beneficial endophytic fungus Piriformospora indica. The expression of BvGLP-1 in Arabidopsis elevated the H(2)O(2) content and conferred significant resistance to V. longisporum and R. solani but did not affect the beneficial interaction with P. indica in seedlings. Microscopic observations revealed a dramatic reduction in the amount of hyphae of the pathogenic fungi on the root surface as well as of fungal mycelium developed inside the roots of transgenic Arabidopsis compared with wild-type plants. Molecular analysis demonstrated that the BvGLP-1 expression in Arabidopsis constitutively activates the expression of a subset of plant defense-related proteins such as PR-1 to PR-4 and PDF1.2 but not PDF2.1 and PDF2.3. In contrast, the PDF2.1 mRNA level was downregulated. These data suggest an important role of BvGLP-1 in establishment of plant defense responses, which follow specific signaling routes that diverge from those induced by the beneficial fungus.

Suppression of heterotrimeric G-protein beta-subunit affects anther shape, pollen development and inflorescence architecture in tobacco.

The role of the heterotrimeric G-protein beta-subunit in plant development was studied in transgenic tobacco (Nicotiana tabacum L.) plants with reduced beta-subunit levels due to the antisense expression of the beta-subunit mRNA. The antisense plants had aberrant anther shape and produced non-germinating pollen. The anthers were sporadically transformed to petals, whereas other floral organs were not affected. The pollen grains were smaller than the wild-type pollen and had abnormal cell walls. The architecture of mature antisense plants was altered. The plants had long branched panicles and short stems. These data suggest that the beta-subunit of the plant heterotrimeric G-proteins is involved in the regulation of the reproductive phase of the tobacco life cycle, particularly in stamen development and pollen maturation.