Cell wall integrity controls root elongation via a general 1-aminocyclopropane-1-carboxylic acid-dependent, ethylene-independent pathway.

Cell expansion in plants requires cell wall biosynthesis and rearrangement. During periods of rapid elongation, such as during the growth of etiolated hypocotyls and primary root tips, cells respond dramatically to perturbation of either of these processes. There is growing evidence that this response is initiated by a cell wall integrity-sensing mechanism and dedicated signaling pathway rather than being an inevitable consequence of lost structural integrity. However, the existence of such a pathway in root tissue and its function in a broader developmental context have remained largely unknown. Here, we show that various types of cell wall stress rapidly reduce primary root elongation in Arabidopsis (Arabidopsis thaliana). This response depended on the biosynthesis of 1-aminocyclopropane-1-carboxylic acid (ACC). In agreement with the established ethylene signaling pathway in roots, auxin signaling and superoxide production are required downstream of ACC to reduce elongation. However, this cell wall stress response unexpectedly does not depend on the perception of ethylene. We show that the short-term effect of ACC on roots is partially independent of its conversion to ethylene or ethylene signaling and that this ACC-dependent pathway is also responsible for the rapid reduction of root elongation in response to pathogen-associated molecular patterns. This acute response to internal and external stress thus represents a novel, noncanonical signaling function of ACC.

Comparative analysis of CAX2-like cation transporters indicates functional and regulatory diversity.

Internal compartmentalization of metals is an important metal tolerance mechanism in many organisms. In plants and fungi, sequestration into the vacuole is a major detoxification mechanism for metals. Cation transport into the vacuole can be mediated by CAX (cation exchanger) transporters. The Arabidopsis thaliana AtCAX2 transporter was shown previously to transport Ca(2+), Cd(2+) and Mn(2+). To assess the conservation of the functional and regulatory characteristics of CAX2-like transporters in higher plants, we have characterized AtCAX2 orthologues from Arabidopsis (AtCAX5), tomato (LeCAX2) and barley (HvCAX2). Substrate specificity and regulatory activity were assessed using a yeast heterologous-expression assay. Each CAX could transport Ca(2+) and Mn(2+) into the yeast vacuole, but they each had different cation transport kinetics. Most notably, there was variation in the regulation of the transporters. As found with AtCAX2 previously, only expression of an N-terminally truncated form of AtCAX5 in yeast was able to mediate Ca(2+) and Mn(2+) transport, indicating that activity may be controlled by an autoregulatory region at the N-terminus. In contrast, either full-length or truncated LeCAX2 could efficiently transport Ca(2+), although Mn(2+) transport was controlled by the N-terminus. HvCAX2 did not appear to possess an N-terminal regulatory domain. Expression of AtCAX2 was not significantly modulated by metal stress; however, AtCAX5 and HvCAX2 were transcriptionally up-regulated by high Mn(2+) treatment, and by Ca(2+) and Na(+) stress respectively. It is therefore apparent that, despite the high sequence identity between plant CAX2 orthologues, there is significant diversity in their functional characteristics, particularly with regard to regulatory mechanisms.

High quality clinical grade human embryonic stem cell lines derived from fresh discarded embryos.

BACKGROUND: Human embryonic stem cells (hESCs) hold tremendous promise for cell replacement therapies for a range of degenerative diseases. In order to provide cost-effective treatments affordable by public health systems, HLA-matched allogeneic tissue banks of the highest quality clinical-grade hESCs will be required. However only a small number of existing hESC lines are suitable for clinical use; they are limited by moral and ethical concerns and none of them apply Good Manufacturing Practice (GMP) standards to the earliest and critical stages of gamete and embryo procurement. We thus aimed to derive new clinical grade hESC lines of highest quality from fresh surplus GMP grade human embryos. METHODS: A comprehensive screen was performed for suitable combinations of culture media with supporting feeder cells or feeder-free matrix, at different stages, to support expansion of the inner cell mass and to establish new hESC lines. RESULTS: We developed a novel two-step and sequential media system of clinical-grade hESC derivation and successfully generated seven new hESC lines of widely varying HLA type, carefully screened for genetic health, from human embryos donated under the highest ethical and moral standards under an integrated GMP system which extends from hESC banking all the way back to gamete and embryo procurement. CONCLUSIONS: The present study, for the first time, reports the successful derivation of highest-quality clinical-grade hESC lines from fresh poor-quality surplus human embryos generated in a GMP-grade IVF laboratory. The availability of hESC lines of this status represents an important step towards more widespread application of regenerative medicine therapies.

A cation-regulated and proton gradient-dependent cation transporter from Chlamydomonas reinhardtii has a role in calcium and sodium homeostasis.

The CrCAX1 gene encoding a Ca2+/H+ and Na+/H+ exchanger was cloned and characterized from the unicellular green alga Chlamydomonas reinhardtii to begin to understand the mechanisms of cation homeostasis in this model organism. CrCAX1 was more closely related to fungal cation exchanger (CAX) genes than those from higher plants but has structural characteristics similar to plant Ca2+/H+ exchangers including a long N-terminal tail. When CrCAX1-GFP was expressed in Saccharomyces cerevisiae, it localized at the vacuole. CrCAX1 could suppress the Ca2+-hypersensitive phenotype of a yeast mutant and mediated proton gradient-dependent Ca2+/H+ exchange activity in vacuolar membrane vesicles. Ca2+ transport activity was increased following N-terminal truncation of CrCAX1, suggesting the existence of an N-terminal auto-regulatory mechanism. CrCAX1 could also provide tolerance to Na+ stress when expressed in yeast or Arabidopsis thaliana because of Na+/H+ exchange activity. This Na+/H+ exchange activity was not regulated by the N terminus of the CrCAX1 protein. A subtle tolerance by CrCAX1 in yeast to Co2+ stress was also observed. CrCAX1 was transcriptionally regulated in Chlamydomonas cells grown in elevated Ca2+ or Na+. This study has thus uncovered a novel eukaryotic proton-coupled transporter, CrCAX1, that can transport both monovalent and divalent cations and that appears to play a role in cellular cation homeostasis by the transport of Ca2+ and Na+ into the vacuole.