Searching iron sensors in plants by exploring the link among 2′-OG-dependent dioxygenases, the iron deficiency response and metabolic adjustments occurring under iron deficiency

Knowledge accumulated on the regulation of iron (Fe) homeostasis, its intracellular trafficking and transport across various cellular compartments and organs in plants; storage proteins, transporters and transcription factors involved in Fe metabolism have been analyzed in detail in recent years. However, the key sensor(s) of cellular plant “Fe status” triggering the long-distance shoot–root signaling and leading to the root Fe deficiency responses is (are) still unknown. Local Fe sensing is also a major task for roots, for adjusting the internal Fe requirements to external Fe availability: how such sensing is achieved and how it leads to metabolic adjustments in case of nutrient shortage, is mostly unknown. Two proteins belonging to the 2′-OG-dependent dioxygenases family accumulate several folds in Fe-deficient Arabidopsis roots. Such proteins require Fe(II) as enzymatic cofactor; one of their subgroups, the HIF-P4H (hypoxia-inducible factor-prolyl 4-hydroxylase), is an effective oxygen sensor in animal cells. We envisage here the possibility that some members of the 2′-OG dioxygenase family may be involved in the Fe deficiency response and in the metabolic adjustments to Fe deficiency or even in sensing Fe, in plant cells

Microtubules play a role in trafficking prevacuolar compartments to vacuoles in tobacco pollen tubes

Fine regulation of exocytosis and endocytosis plays a basic role in pollen tube growth. Excess plasma membrane secreted during pollen tube elongation is known to be retrieved by endocytosis and partially reused in secretory pathways through the Golgi apparatus. Dissection of endocytosis has enabled distinct degradation pathways to be identified in tobacco pollen tubes and has shown that microtubules influence the transport of plasma membrane internalized in the tip region to vacuoles. Here we used different drugs affecting the polymerization state of microtubules together with SYP21, a marker of prevacuolar compartments, to characterize trafficking of prevacuolar compartments in Nicotiana tabacum pollen tube. Ultrastructural and biochemical analysis showed that microtubules bind SYP21-positive microsomes. Transient transformation of pollen tubes with LAT52-YFP-SYP21 revealed that microtubules play a key role in the delivery of prevacuolar compartments to tubular vacuoles

The impact of the absence of aliphatic glucosinolates on water transport under salt stress in Arabidopsis thaliana

Members of the Brassicaceae are known for their contents of nutrients and health-promoting phytochemicals, including glucosinolates. Exposure to salinity increases the levels of several of these compounds, but their role in abiotic stress response is unclear. The effect of aliphatic glucosinolates on plant water balance and growth under salt stress, involving aquaporins, was investigated by means of Arabidopsis thaliana mutants impaired in aliphatic glucosinolate biosynthesis, which is controlled by two transcription factors: Myb28 and Myb29. The double mutant myb28myb29, completely lacking aliphatic glucosinolates, was compared to wild type Col-0 (WT) and the single mutant myb28. A greater reduction in the hydraulic conductivity of myb28myb29 was observed under salt stress, when compared to the WT and myb28; this correlated with the abundance of both PIP1 and PIP2 aquaporin subfamilies. Also, changes in root architecture in response to salinity were genotype dependent. Treatment with NaCl altered glucosinolates biosynthesis in a similar way in WT and the single mutant and differently in the double mutant. The results indicate that short-chain aliphatic glucosinolates may contribute to water saving under salt stress.This work was supported by the following Spanish Ministry of Science and Innovation R&D and innovation programs AGL2009-12720 and Ramón y Cajal' (Ref RYC-2009-04574).Peer reviewedPeer Reviewe

cROStalk for Life: Uncovering ROS Signaling in Plants and Animal Systems, from Gametogenesis to Early Embryonic Development

This review explores the role of reactive oxygen species (ROS)/Ca2+ in communication within reproductive structures in plants and animals. Many concepts have been described during the last years regarding how biosynthesis, generation products, antioxidant systems, and signal transduction involve ROS signaling, as well as its possible link with developmental processes and response to biotic and abiotic stresses. In this review, we first addressed classic key concepts in ROS and Ca2+ signaling in plants, both at the subcellular, cellular, and organ level. In the plant science field, during the last decades, new techniques have facilitated the in vivo monitoring of ROS signaling cascades. We will describe these powerful techniques in plants and compare them to those existing in animals. Development of new analytical techniques will facilitate the understanding of ROS signaling and their signal transduction pathways in plants and mammals. Many among those signaling pathways already have been studied in animals; therefore, a specific effort should be made to integrate this knowledge into plant biology. We here discuss examples of how changes in the ROS and Ca2+ signaling pathways can affect differentiation processes in plants, focusing specifically on reproductive processes where the ROS and Ca2+ signaling pathways influence the gametophyte functioning, sexual reproduction, and embryo formation in plants and animals. The study field regarding the role of ROS and Ca2+ in signal transduction is evolving continuously, which is why we reviewed the recent literature and propose here the potential targets affecting ROS in reproductive processes. We discuss the opportunities to integrate comparative developmental studies and experimental approaches into studies on the role of ROS/ Ca2+ in both plant and animal developmental biology studies, to further elucidate these crucial signaling pathways

Identification of an Arabidopsis mitoferrinlike carrier protein involved in Fe metabolism

Iron has a major role in mitochondrial as well as in chloroplast metabolism, however the processes involved in organelle iron transport in plants are only partially understood. To identify mitochondrial iron transporters in Arabidopsis, we searched for proteins homologous to the Danio rerio (zebrafish) Mitoferrin2 MFRN2, a mitochondrial iron importer in non-erythroid cells. Among the identified putative Arabidopsis mitoferrinlike proteins, we focused on that one encoded by At5g42130, which we named AtMfl1 (MitoFerrinLike1). AtMfl1 expression strongly correlates with genes coding for proteins involved in chloroplast metabolism. Such an unexpected result is supported by the identification by different research groups, of the protein encoded by At5g42130 and of its homologs from various plant species in the inner chloroplastic envelope membrane proteome. Notably, neither the protein encoded by At5g42130 nor its homologs from other plant species have been identified in the mitochondrial proteome. AtMfl1 gene expression is dependent on Fe supply: AtMfl1 transcript strongly accumulates under Fe excess, moderately under Fe sufficiency and weakly under Fe deficiency. In order to understand the physiological role of AtMfl1, we isolated and characterized two independent AtMfl1 KO mutants, atmfl1-1 and atmfl1-2: both show reduced vegetative growth. When grown under conditions of Fe excess, atmfl1-1 and atmfl1-2 mutants (seedlings, rosette leaves) contain less total Fe than wt and also reduced expression of the iron storage ferritin AtFer1. Taken together, these results suggest that Arabidopsis mitoferrinlike gene AtMfl1 is involved in Fe transport into chloroplasts, under different conditions of Fe supply and that suppression of its expression alters plant Fe accumulation in various developmental stages.Fil: Tarantino, Delia. Universita Degli Studi Di Milano; ItaliaFil: Morandini, Piero. Universita Degli Studi Di Milano; ItaliaFil: Ramírez, Leonor. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Mar del Plata. Instituto de Investigaciones Biológicas; Argentina. Universita Degli Studi Di Milano; Italia. Universidad Nacional de Mar del Plata; ArgentinaFil: Soave, Carlo. Universita Degli Studi Di Milano; ItaliaFil: Murgia, Irene. Universita Degli Studi Di Milano; Itali

Cleaning the Medicago Microarray Database to Improve Gene Function Analysis

Transcriptomics studies have been facilitated by the development of microarray and RNA-Seq technologies, with thousands of expression datasets available for many species. However, the quality of data can be highly variable, making the combined analysis of different datasets difficult and unreliable. Most of the microarray data for Medicago truncatula, the barrel medic, have been stored and made publicly accessible on the web database Medicago truncatula Gene Expression atlas (MtGEA). The aim of this work is to ameliorate the quality of the MtGEA database through a general method based on logical and statistical relationships among parameters and conditions. The initial 716 columns available in the dataset were reduced to 607 by evaluating the quality of data through the sum of the expression levels over the entire transcriptome probes and Pearson correlation among hybridizations. The reduced dataset shows great improvements in the consistency of the data, with a reduction in both false positives and false negatives resulting from Pearson correlation and GO enrichment analysis among genes. The approach we used is of general validity and our intent is to extend the analysis to other plant microarray databases

Editorial

[No abstract available

Analysis of the transgenerational iron deficiency stress memory in Arabidopsis thaliana plants.

We investigated the existence of the transgenerational memory of iron (Fe) deficiency stress, in Arabidopsis thaliana. Plants were grown under Fe deficiency/sufficiency, and so were their offspring. The frequency of Somatic Homologous Recombination (SHR) events, of DNA strand breaks as well as the expression of the transcription elongation factor TFIIS-like gene increase when plants are grown under Fe deficiency. However, SHR frequency, DNA strand break events and TFIIS-like gene expression do not increase further when plants are grown for more than one generation under the same stress, and furthermore, they decrease back to control values within two succeeding generations grown under control conditions, regardless of the Fe deficiency stress history of the mother plants.Seedlings produced from plants grown under Fe deficiency evolve more oxygen than control seedlings, when grown under Fe sufficiency: however, this trait is not associated with any change in the protein profile of the photosynthetic apparatus and is not transmitted to more than one generation. Lastly, plants grown for multiple generations under Fe deficiency produce seeds with greater longevity: however this trait is not inherited in offspring generations unexposed to stress. These findings suggest the existence of multiple-step control of mechanisms to prevent a genuine and stable transgenerational transmission of Fe deficiency stress memory, with the tightest control on DNA integrity