Nice to meet you: genetic, epigenetic and metabolic controls of plant perception of beneficial associative and endophytic diazotrophic bacteria in non-leguminous plants.

A wide range of rhizosphere diazotrophic bacteria are able to establish beneficial associations with plants, being able to associate to root surfaces or even endophytically colonize plant tissues. In common, both associative and endophytic types of colonization can result in beneficial outcomes to the plant leading to plant growth promotion, as well as increase in tolerance against biotic and abiotic stresses. An intriguing question in such associations is how plant cell surface perceives signals from other living organisms, thus sorting pathogens from beneficial ones, to transduce this information and activate proper responses that will finally culminate in plant adaptations to optimize their growth rates. This review focuses on the recent advances in the understanding of genetic and epigenetic controls of plant-bacteria signaling and recognition during beneficial associations with associative and endophytic diazotrophic bacteria. Finally, we propose that "soil-rhizosphere-rhizoplane-endophytes-plant" could be considered as a single coordinated unit with dynamic components that integrate the plant with the environment to generate adaptive responses in plants to improve growth. The homeostasis of the whole system should recruit different levels of regulation, and recognition between the parties in a given environment might be one of the crucial factors coordinating these adaptive plant responses.

Nitrogen signalling in plant interactions with associative and endophytic diazotrophic bacteria.

Some beneficial plant-interacting bacteria can biologically fix N2 to plant-available ammonium. Biological nitrogen fixation (BNF) is an important source of nitrogen (N) input in agriculture and represents a promising substitute for chemical N fertilizers. Diazotrophic bacteria have the ability to develop different types of root associations with different plant species. Among the highest rates of BNF are those measured in legumes nodulated by endosymbionts, an already very well documented model of plant-diazotrophic bacterial association. However, it has also been shown that economically important crops, especially monocots, can obtain a substantial part of their N needs from BNF by interacting with associative and endophytic diazotrophic bacteria, that either live near the root surface or endophytically colonize intercellular spaces and vascular tissues of host plants. One of the best reported outcomes of this association is the promotion of plant growth by direct and indirect mechanisms. Besides fixing N, these bacteria can also produce plant growth hormones, and some species are reported to improve nutrient uptake and increase plant tolerance against biotic and abiotic stresses. Thus, this particular type of plant-bacteria association consists of a natural beneficial system to be explored; however, the regulatory mechanisms involved are still not clear. Plant N status might act as a key signal, regulating and integrating various metabolic processes that occur during association with diazotrophic bacteria. This review will focus on the recent progress in understanding plant association with associative and endophytic diazotrophic bacteria, particularly on the knowledge of the N networks involved in BNF and in the promotion of plant growth.

Characterization and partial isolation of ouabain-insensitive Na(+) -ATPase in MDCK I cells.

We show that MDCK I cells express, besides the classical (Na(+)+K(+))ATPase, a Na(+)-stimulated ATPase activity with the following characteristics: (1) K(0.5) for Na(+) 7.5+/-1.5 mM and V(max) 23.12+/-1.1 nmol Pi/mg per min; (2) insensitive to 1 mM ouabain and 30 mM KCl; and (3) inhibited by furosemide and vanadate (IC(50) 42.1+/-8.0 and 4.3+/-0.3 microM, respectively). This enzyme forms a Na(+)-stimulated, furosemide- and hydroxylamine-sensitive ATP-driven acylphosphate phosphorylated intermediate with molecular weight of 100 kDa. Immunoprecipitation of the (Na(+)+K(+))ATPase with monoclonal anti-alpha(1) antibody reduced its activity in the supernatant by 90%; the Na(+)-ATPase activity was completely maintained. In addition, the formation of the Na(+)-stimulated, furosemide- and hydroxylamine-sensitive ATP-driven acylphosphate intermediate occurred at the same magnitude as that observed before immunoprecipitation. These data suggest that Na(+)-ATPase and (Na(+)+K(+))ATPase activities are independent, with Na(+)-ATPase belonging to a different enzyme entity.

PI-PLCbeta is involved in the modulation of the proximal tubule Na+-ATPase by angiotensin II.

In previous papers we showed that Ang II increases the proximal tubule Na+-ATPase activity through AT1/PKC pathway [L.B. Rangel, C. Caruso-Neves, L.S. Lara, A.G. Lopes, Angiotensin II stimulates renal proximal tubule Na+-ATPase activity through the activation of protein kinase C. Biochim. Biophys. Acta 1564 (2002) 310-316, L.B.A. Rangel, A.G. Lopes, L.S. Lara, C. Caruso-Neves, Angiotensin II stimulates renal proximal tubule Na+)-ATPase activity through the activation of protein kinase C. Biochim. Biophys. Acta 1564 (2002) 310-316]. In the present paper, we study the involvement of PI-PLCbeta on the stimulatory effect of angiotensin II (Ang II) on the proximal tubule Na+-ATPase activity. Western blotting assays, using a polyclonal antibody for PI-PLCbeta, show a single band of about 150 KDa, which correspond to PI-PLCbeta isoforms. Ang II induces a rapid decrease in PIP2 levels, a PI-PLCbeta substrate, being the maximal effect observed after 30 s incubation. This effect of Ang II is completely abolished by 5 x 10(-8) M U73122, a specific inhibitor of PI-PLCbeta. In this way, the effect of 10(-8) M Ang II on the proximal tubule basolateral membrane (BLM) Na+-ATPase activity is completely abolished by 5 x 10(-8) M U73122. The increase in diacylglycerol (DAG) concentration, an product of PI-PLCbeta, from 0.1 to 10 nM raises the Na+-ATPase activity from 6.1+/-0.2 to 13.1+/-1.8 nmol Pi mg(-1) min(-1). This effect is similar and non-additive to that observed with Ang II. Furthermore, the stimulatory effect of 10 nM DAG is completely reversed by 10(-8) M calphostin C (Calph C), an inhibitor of PKC. Taken together these data indicate that Ang II stimulates the Na+-ATPase activity of proximal tubule BLM through a PI-PLCbeta/PKC pathway.