Inside out: root cortex-localized LHK1 cytokinin receptor limits epidermal infection of Lotus japonicus roots by Mesorhizobium loti.

During Lotus japonicus-Mesorhizobium loti symbiosis, the LOTUS HISTIDINE KINASE1 (LHK1) cytokinin receptor regulates both the initiation of nodule formation and the scope of root infection. However, the exact spatiotemporal mechanism by which this receptor exerts its symbiotic functions has remained elusive. In this study, we performed cell type-specific complementation experiments in the hyperinfected lhk1-1 mutant background, targeting LHK1 to either the root epidermis or the root cortex. We also utilized various genetic backgrounds to characterize expression of several genes regulating symbiotic infection. We show here that expression of LHK1 in the root cortex is required and sufficient to regulate both nodule formation and epidermal infections. The LHK1-dependent signalling that restricts subsequent infection events is triggered before initial cell divisions for nodule primordium formation. We also demonstrate that AHK4, the Arabidopsis orthologue of LHK1, is able to regulate M. loti infection in L. japonicus, suggesting that an endogenous cytokinin receptor could be sufficient for engineering nitrogen-fixing root nodule symbiosis in nonlegumes. Our data provide experimental evidence for the existence of an LHK1-dependent root cortex-to-epidermis feedback mechanism regulating rhizobial infection. This root-localized regulatory module functionally links with the systemic autoregulation of nodulation (AON) to maintain the homeostasis of symbiotic infection.

Delivery of antiangiogenic and antioxidant drugs of ophthalmic interest through a nanoporous inorganic filter.

PURPOSE: We propose a novel method of administration of antiangiogenic and antioxidant drugs, with potential clinical application in the treatment of proliferative diabetic retinopathy (PDR) and age-related macular degeneration (AMD). We suggest the encapsulation of drugs in implantable sustained release devices, limited by membranes with pores in the tens of nanometers diameter range, which display a slower, quasi-linear release kinetics, and a better selectivity than other membranes. In this paper we explored the feasibility of this approach by testing in vitro several key elements of the nanofilter system: diffusion of drugs of interest, efficacy in producing desirable effects on cells, and biocompatibility of used material with some of the cells encountered in the ocular cavity. METHODS: We used an aluminum oxide filter (Anopore) with pores of 20 nm as a limiting medium for the administration of drugs. First, we induced an oxidative stress in human retinal endothelial cells (HREC) by treating them with hydrogen peroxide diffused across the filter, in the absence or in the presence of catalase. HREC attached to the culture plate, or emerging as angiogenic sprouts from aggregates embedded in collagen gels, were also exposed to vitamin C or to endostatin delivered across the nanoporous filter. Direct exposure of the cells to the agents served as positive controls. Growth of cells on the filter was considered an indication for biocompatibility. RESULTS: Catalase diffused across the nanoporous membrane counteracted the cytotoxic effect of hydrogen peroxide on HREC. We also found that vitamin C, acting directly or after diffusion across the filter, up to concentrations physiologically present in the eye, was a concentration dependent modulator of HREC's ability to survive and sprout. Additionally, we confirmed the ability of endostatin to block the growth of HREC either attached or sprouting from cell aggregates, after diffusion across the Anopore nanofilter. CONCLUSIONS: The drug delivery method based on the administration of angiostatic and antioxidant agents across the inorganic aluminum oxide nanoporous filter passed the key in vitro tests for diffusibility and biocompatibility, opening the way for medical applications.