BAK1 is a coreceptor and positive regulator of multiple ligand binding leucine-rich repeat receptor kinases (LRR-RKs) and is involved in brassinosteroid (BR)-dependent growth and development, innate immunity, and cell death control. The BAK1-interacting LRR-RKs BIR2 and BIR3 were previously identified by proteomics analyses of in vivo BAK1 complexes. Here, we show that BAK1-related pathways such as innate immunity and cell death control are affected by BIR3 in Arabidopsis thaliana. BIR3 also has a strong negative impact on BR signaling. BIR3 directly interacts with the BR receptor BRI1 and other ligand binding receptors and negatively regulates BR signaling by competitive inhibition of BRI1. BIR3 is released from BAK1 and BRI1 after ligand exposure and directly affects the formation of BAK1 complexes with BRI1 or FLAGELLIN SENSING2. Double mutants of bak1 and bir3 show spontaneous cell death and constitutive activation of defense responses. BAK1 and its closest homolog BKK1 interact with and are stabilized by BIR3, suggesting that bak1 bir3 double mutants mimic the spontaneous cell death phenotype observed in bak1 bkk1 mutants via destabilization of BIR3 target proteins. Our results provide evidence for a negative regulatory mechanism for BAK1 receptor complexes in which BIR3 interacts with BAK1 and inhibits ligand binding receptors to prevent BAK1 receptor complex formation.

BACKGROUND:Transmembrane leucine-rich repeat (LRR) receptors are commonly used innate immune receptors in plants and animals but can also sense endogenous signals to regulate development. BAK1 is a plant LRR-receptor-like kinase (RLK) that interacts with several ligand-binding LRR-RLKs to positively regulate their functions. BAK1 is involved in brassinosteroid-dependent growth and development, innate immunity, and cell-death control by interacting with the brassinosteroid receptor BRI1, immune receptors, such as FLS2 and EFR, and the small receptor kinase BIR1, respectively.RESULTS:Identification of in vivo BAK1 complex partners by LC/ESI-MS/MS uncovered two novel BAK1-interacting RLKs, BIR2 and BIR3. Phosphorylation studies revealed that BIR2 is unidirectionally phosphorylated by BAK1 and that the interaction between BAK1 and BIR2 is kinase-activity dependent. Functional analyses of bir2 mutants show differential impact on BAK1-regulated processes, such as hyperresponsiveness to pathogen-associated molecular patterns (PAMP), enhanced cell death, and resistance to bacterial pathogens, but have no effect on brassinosteroid-regulated growth. BIR2 interacts constitutively with BAK1, thereby preventing interaction with the ligand-binding LRR-RLK FLS2. PAMP perception leads to BIR2 release from the BAK1 complex and enables the recruitment of BAK1 into the FLS2 complex.CONCLUSIONS:Our results provide evidence for a new regulatory mechanism for innate immune receptors with BIR2 acting as a negative regulator of PAMP-triggered immunity by limiting BAK1-receptor complex formation in the absence of ligands.

Amino acid transporters in plants are crucial for distributing amino acids between plant organs and cellular compartments. The H+-coupled plasma membrane transporter CAT1 (cationic amino acid transporter 1) facilitates the high-affinity uptake of basic amino acids. The uptake of lysine (Lys) via the roots was not altered in loss-of-function mutants, in accordance with the minor expression of CAT1 in roots, but plants ectopically overexpressing CAT1 incorporated Lys at higher rates. Exogenous Lys inhibited the primary root of Arabidopsis, whereas lateral roots were stimulated. These effects were augmented by the presence or absence of CAT1. Furthermore, the total biomass of soil-grown plants ectopically overexpressing CAT1 was reduced and the time to flowering was accelerated. These effects were accompanied by only minor changes in the overall amino acid profile. Interestingly, CAT1 belongs to a specific small cluster of nitrogen-containing metabolite transporter genes that are rapidly up-regulated upon infection with Pseudomonas syringae and that may participate in the systemic response of plants to pathogen attack. The overexpression of CAT1 indeed enhanced the resistance to the hemibiotrophic bacterial pathogen P.syringae via a constitutively activated salicylic acid (SA) pathway, which is consistent with the developmental defects and the resistance phenotype.The cationic amino acid transporter gene CAT1 was identified as part of a transcriptional pathogen response and its over-expression negatively affected the biomass, but improved the defense against pathogens via salicylic acid.

Plasma membrane-borne pattern recognition receptors, which recognize microbe-associated molecular patterns and endogenous damage-associated molecular patterns, provide the first line of defense in innate immunity. In plants, leucine-rich repeat receptor kinases fulfill this role, as exemplified by FLS2 and EFR, the receptors for the microbe-associated molecular patterns flagellin and elongation factor Tu. Here we examined the perception of the damage-associated molecular pattern peptide 1 (AtPep1), an endogenous peptide of Arabidopsis identified earlier and shown to be perceived by the leucine-rich repeat protein kinase PEPR1. Using seedling growth inhibition, elicitation of an oxidative burst and induction of ethylene biosynthesis, we show that wild type plants and the pepr1 and pepr2 mutants, affected in PEPR1 and in its homologue PEPR2, are sensitive to AtPep1, but that the double mutant pepr1/pepr2 is completely insensitive. As a central body of our study, we provide electrophysiological evidence that at the level of the plasma membrane, AtPep1 triggers a receptor-dependent transient depolarization through activation of plasma membrane anion channels, and that this effect is absent in the double mutant pepr1/pepr2. The double mutant also fails to respond to AtPep2 and AtPep3, two distant homologues of AtPep1 on the basis of homology screening, implying that the PEPR1 and PEPR2 are responsible for their perception too. Our findings provide a basic framework to study the biological role of AtPep1-related danger signals and their cognate receptors.

Plant receptor-like kinases (RLKs) are transmembrane proteins with putative N-terminal extracellular ligand-binding domains and C-terminal intracellular protein kinase domains. RLKs have been implicated in multiple physiological programs including plant development and immunity to microbial infection. Arabidopsis thaliana gene expression patterns support an important role of this class of proteins in biotic stress adaptation. Here, we provide a comprehensive survey of plant immunity-related RLK gene expression. We further document the role of the Arabidopsis Brassinosteroid Insensitive 1 (BRI1)-associated receptor kinase 1 (BAK1) in seemingly unrelated biological processes, such as plant development and immunity, and propose a role of this protein as an adaptor molecule that is required for proper functionality of numerous RLKs. This view is supported by the identification of an additional RLK, PEPR1, and its closest homolog, PEPR2 as BAK1-interacting RLKs.

Research of the last decade has revealed that plant immunity consists of different layers of defense that have evolved by the co-evolutional battle of plants with its pathogens. Particular light has been shed on PAMP- (pathogen-associated molecular pattern) triggered immunity (PTI) mediated by pattern recognition receptors. Striking similarities exist between the plant and animal innate immune system that point for a common optimized mechanism that has evolved independently in both kingdoms. Pattern recognition receptors (PRRs) from both kingdoms consist of leucine-rich repeat receptor complexes that allow recognition of invading pathogens at the cell surface. In plants, PRRs like FLS2 and EFR are controlled by a co-receptor SERK3/BAK1, also a leucine-rich repeat receptor that dimerizes with the PRRs to support their function. Pathogens can inject effector proteins into the plant cells to suppress the immune responses initiated after perception of PAMPs by PRRs via inhibition or degradation of the receptors. Plants have acquired the ability to recognize the presence of some of these effector proteins which leads to a quick and hypersensitive response to arrest and terminate pathogen growth.

An efficient system was established for high frequency embryogenesis and regeneration of indica rice, Oryza sativa L. cv. MDU 5. Basic media, carbohydrate sources and concentrations, agar concentrations, amino acids, cytokinins and auxins were evaluated in callus induction and regeneration media to establish the most efficient regeneration protocol for MDU 5 indica rice. The optimized callus induction and regeneration media consisted of the basic MS salt mixtures and vitamin solutions supplemented with 4% maltose, 1g/L casein hydrolysate and 50 mg/L tryptophan, solidified with 1% agar. The callus induction medium was supplemented with 2,4−D 2 mg/L, kinetin 0.5 mg/L, indole acetic acid 1 mg/L, and 6−benzyl aminopurine 0.5 mg/L whereas the media for regeneration phase comprised kinetin 2 mg/L, indole acetic acid 1 mg/L and 6−benzyl aminopurine 2 mg/L. The media optimized for MDU 5 was analyzed for response of 73 other indica genotypes. Of these indica varieties 64 genotypes yielded 98.5% callus induction within eight days, 59% embryogenic calli formation, initiation of multiple green buds within eight days and a regeneration rate of 90%. The embryogenic calli derived were used for transformation with Agrobacterium tumifaciens (LBA 4404 or EHA 101 strains). Two binary vectors (pKHG4 and pIG121Hm) containing hph and GUS genes were used in these transformation studies. Fifty-one genotypes responded to the optimized media by producing hygromycin−resistant calli. The -histochemical test for s−glucuronidase activity was positive from 32 genotypes with the transformation efficiencies ranging between 7.0% and 8.3%.

The world is moving into a period of widespread water stress and competition,with enormous implications for food security, the health of the aquatic environment,and social and political stability. In the second half of the 20th Century water demand more than tripled,the major factor being irrigation for food production. Over the same period,the number of large dams worldwide climbed from 5,000 to 45,000 - bringing about a major alteration of river hydrology and ecosystem function. Rivers have been disconnected from portions of their channels, their floodplains, their deltas, and from the seas into which they empty. The resulting loss of aquatic habitat has put freshwater life in grave jeopardy. In the 21st Century it will be possible to satisfy the needs of 8-9 billion people while protecting the health of aquatic ecosystems,but only with a fundamental shift in the way society uses, manages and values freshwater. It will likely require a doubling of water productivity over the next 25 years - including more efficient irrigation practices and greater recycling of wastewater. To guide policy, nations need to systematically determine their freshwater ecosystem flow requirements in a way that perhaps only South Africa is attempting so far. Underpinning all these measures is the need for a guiding water ethic that states that enough water should be provided for all living things before some get more than enough.

Water scarcity in some regions is a leading source of economic and political instability. Upstream countries have a clear advantage over downstream countries. Almost 40% of the world's population relies on river systems used by at least 2 countries. Water conflicts are most evident in the Middle East where population growth rates are among the world's highest and agricultural productivity depends almost exclusively on irrigation. Water scarcity is most critical in the Jordan River basin which Israel, Jordan, the occupied West Bank, and part of Syria share. Israel exceeds its renewable water supply by 15%. Even though Jordanians use less than 50% of the water/capita Israel uses, its population grows 3.4%/year of Israel's water supply is the Yarqon-Taninim aquifer whose recharge area is on the West Bank. Israel draws water from this aquifer for its own use, but does not let West Bank Arabs draw from it. Another water supply lies in the Golan Heights with Israel seized from Syria. Its other source is an overpumped coastal aquifer. 9 nations claim the Nile with Egypt being the last country to receive its waters. Egypt has very few of its own water sources plus is has rapid population growth. Turkey plans on constructing 22 dams, 19 hydropower stations, and 25 irrigation systems on the Euphrates river, resulting in a 35% reduction in water flow to Syria in normal years and even more in dry years. This project would also pollute the river with irrigation runoff. International cooperation is needed to address wait crisis. Israel could share its drip irrigation technology with others, such as it has done with the Islamic Central Asian republics. Ethiopia could store Nile water in its highlands which have a lower evaporation rate than that at Egypt's Aswan Dam, resulting in more available water. Perhaps the mutual gains possible from cooperation will unite long standing enemies toward peace.

THE study of thyroid gland disease has been hampered by technical obstacles to measurement of thyroid stimulating hormone (TSH) in human blood. Application of several bioassay techniques, including the very sensitive tadpole method of D'Angelo, has so far yielded fragmentary or contradictory data (Hertz and Oastler, 1936; Fellinger, 1936; DeRobertis, 1948; d'Angelo et al., 1951; Asboe-Hansen et al., 1952; Gilliland and Strudwick, 1953; Simkin et at., 1953; Adams and Purves, 1953; Sampson et al., 1954). Most of these bioassays have been made on whole serum without pretreatment aimed at isolation of the TSH activity. The importance of isolating the active fraction was emphasized by Fellinger (1936) who found that serum TSH effects were more than doubled by acetone precipitation of hemolyzed whole blood and ascribed the augmented TSH biopotency to the elimination of thyroxin. Similarly, DeRobertis (1948) observed no detectable TSH activity in blood prior to acetone precipitation.

THIS report documents (1) production of fetal goiter when perchlorate is administered to pregnant guinea pigs, (2) failure of large doses of triiodothyronine to protect the fetus against perchlorate induced goiter, and (3) studies on the placental transfer of I131 labeled triiodothyronine. The findings bear upon the use of these agents in the treatment of thyroid diseases during pregnancy. In addition, they may be relevant to broader aspects of fetal-maternal interrelations.