Publikationen - Molekulare Signalverarbeitung

The Lotus japonicus SYMBIOSIS RECEPTOR-LIKE KINASE (SYMRK) is required for symbiotic signal transduction upon stimulation of root cells by microbial signaling molecules. Here, we identified members of the SEVEN IN ABSENTIA (SINA) E3 ubiquitin-ligase family as SYMRK interactors and confirmed their predicted ubiquitin-ligase activity. In Nicotiana benthamiana leaves, SYMRK–yellow fluorescent protein was localized at the plasma membrane, and interaction with SINAs, as determined by bimolecular fluorescence complementation, was observed in small punctae at the cytosolic interface of the plasma membrane. Moreover, fluorescence-tagged SINA4 partially colocalized with SYMRK and caused SYMRK relocalization as well as disappearance of SYMRK from the plasma membrane. Neither the localization nor the abundance of Nod-factor receptor1 was altered by the presence of SINA4. SINA4 was transcriptionally upregulated during root symbiosis, and rhizobia inoculated roots ectopically expressing SINA4 showed reduced SYMRK protein levels. In accordance with a negative regulatory role in symbiosis, infection thread development was impaired upon ectopic expression of SINA4. Our results implicate SINA4 E3 ubiquitin ligase in the turnover of SYMRK and provide a conceptual mechanism for its symbiosis-appropriate spatio-temporal containment.

Plant receptor-like kinases (RLKs) function in diverse signaling pathways, including the responses to microbial signals in symbiosis and defense. This versatility is achieved with a common overall structure: an extracytoplasmic domain (ectodomain) and an intracellular protein kinase domain involved in downstream signal transduction. Various surfaces of the leucine-rich repeat (LRR) ectodomain superstructure are utilized for interaction with the cognate ligand in both plant and animal receptors. RLKs with lysin-motif (LysM) ectodomains confer recognitional specificity toward N-acetylglucosamine-containing signaling molecules, such as chitin, peptidoglycan (PGN), and rhizobial nodulation factor (NF), that induce immune or symbiotic responses. Signaling downstream of RLKs does not follow a single pattern; instead, the detailed analysis of brassinosteroid (BR) signaling, innate immunity, and symbiosis revealed at least three largely nonoverlapping pathways. In this review, we focus on RLKs involved in plant-microbe interactions and contrast the signaling pathways leading to symbiosis and defense.

Prosopis strombulifera, a common legume in high-salinity soils of Argentina, is a useful model for elucidation of salt tolerance mechanisms and specific biochemical pathways in halophytes, since its NaCl tolerance exceeds the limit described for most halophytic plants. We analyzed the effects of the increasing concentration of two main soil salts, Na2SO4 and NaCl, on growth parameters of P. strombulifera, chlorophyll levels, and content of jasmonates (JAs) and polyamines (PAs), which are key molecules involved in stress responses. P. strombulifera showed a halophytic response (growth promotion) to NaCl, but strong growth inhibition by iso-osmotic solutions of Na2SO4. Chlorophyll levels, number of leaves and leaf area were also differentially affected. An important finding was the partial alleviation of SO42− toxicity by treatment with two-salt mixture. JAs are not directly involved in salt tolerance in this species since its levels decrease under all salt treatments. Beneficial effects of Putrescine (Put) accumulation in NaCl treated plants maybe inferred probably associated with the antioxidative defense system. Another novel finding is the accumulation of the uncommon PA cadaverine in roots under high Na2SO4, which may be related to SO42− toxicity.

This chapter focuses on Ophioviridae family whose sole member genus is Ophiovirus. The member species of the genus include Citrus psorosis virus (CPsV), Freesia sneak virus(FreSV), Lettuce ring necrosis virus (LRNV), and Mirafiori lettuce big-vein virus (MiLBVV).The single stranded negative/possibly ambisense RNA genome is divided into 3–4 segments, each of which is encapsidated in a single coat protein (43–50 kDa) forming filamentous virions of about 3 nm in diameter, in shape of kinked or probably internally coiled circles of at least two different contour lengths. Ophioviruses can be mechanically transmitted to a limited range of test plants, inducing local lesions and systemic mottle. The natural hosts of CPsV, ranunculus white mottle virus (RWMV), MiLBVV, and LRNV are dicotyledonous plants of widely differing taxonomy. CPsV has a wide geographical distribution in citrus in the Americas, in the Mediterranean and in New Zealand. FreSV has been reported in two species of the family Ranunculacae from Northern Italy, and in lettuce in France and Germany. Tulip mild mottle mosaic virus (TMMMV) has been reported in tulips in Japan. LRNV is closely associated with lettuce ring necrosis disease in The Netherlands, Belgium, and France, and FreSV has been reported in Europe, Africa, North America and New Zealand.

In the present paper we study the possible biological relevance of endogenous jasmonic acid (JA) and exogenous salicylic acid (SA) in a plant-microbial system maize-virus. The virus disease "Mal de Río Cuarto" is caused by the maize rough dwarf virus - Río Cuarto. The characteristic symptoms are the appearance of galls or "enations" in leaves, shortening of the stem internodes, poor radical system and general stunting. Changes in JA and protein pattern in maize control and infected plants of a virus-tolerant cultivar were investigated. Healthy and infected-leaf discs were collected for JA measurement at different post-infection times (20, 40, 60 and 68 days). JA was also measured in roots on day 60 after infection. For SDS-PAGE protein analysis, leaf discs were also harvested on day 60 after infection. Infected leaves showed higher levels of JA than healthy leaves, and the rise in endogenous JA coincided with the enation formation. The soluble protein amount did not show differences between infected and healthy leaves; moreover, no difference in the expression of soluble protein was revealed by SDS-PAGE. Our results show that the octadecanoid pathway was stimulated in leaves and roots of the tolerant maize cultivar when infected by this virus. This finding, together with fewer plants with the disease symptoms, suggest that higher foliar and roots JA content may be related to disease tolerance. SA exogenous treatment caused the reversion of the dwarfism symptom.

Among the multiple environmental signals and hormonal factors regulatingpotato plant morphogenesis and controlling tuber induction, jasmonates (JAs)andgibberellins (GAs) are important components of the signalling pathways in theseprocesses. In the present study, with Solanum tuberosum L.cv. Spunta, we followed the endogenous changes of JAs and GAs during thedevelopmental stages of soil-grown potato plants. Foliage at initial growthshowed the highest jasmonic acid (JA) concentration, while in roots the highestcontent was observed in the stage of tuber set. In stolons at the developmentalstage of tuber set an important increase of JA was found; however, in tubersthere was no change in this compound during tuber set and subsequent growth.Methyl jasmonate (Me-JA) in foliage did not show the same pattern as JA; Me-JAdecreased during the developmental stages in which it was monitored, meanwhileJA increased during those stages. The highest total amount of JAs expressed asJA + Me-JA was found at tuber set. A very important peak ofJA in roots was coincident with that observed in stolons at tuber set. Also, aprogressive increase of this compound in roots was shown during the transitionof stolons to tubers. Of the two GAs monitored, gibberellic acid(GA3) was the most abundant in all the organs. While GA1and GA3 were also found in stolons at the time of tuber set, noothermeasurements of GAs were obtained for stolons at previous stages of plantdevelopment. Our results indicate that high levels of JA and GAs are found indifferent tissues, especially during stolon growth and tuber set.