SEC14-GOLD protein PATELLIN2 binds IRON-REGULATED TRANSPORTER1 linking root iron uptake to vitamin E

GmABCG5, an ATP-binding cassette G transporter gene, is involved in the iron deficiency response in soybean

Iron deficiency is a major nutritional problem causing iron deficiency chlorosis (IDC) and yield reduction in soybean, one of the most important crops. The ATP-binding cassette G subfamily plays a crucial role in substance transportation in plants. In this study, we cloned the GmABCG5 gene from soybean and verified its role in Fe homeostasis. Analysis showed that GmABCG5 belongs to the ABCG subfamily and is subcellularly localized at the cell membrane. From high to low, GmABCG5 expression was found in the stem, root, and leaf of young soybean seedlings, and the order of expression was flower, pod, seed stem, root, and leaf in mature soybean plants. The GUS assay and qRT-PCR results showed that the GmABCG5 expression was significantly induced by iron deficiency in the leaf. We obtained the GmABCG5 overexpressed and inhibitory expressed soybean hairy root complexes. Overexpression of GmABCG5 promoted, and inhibition of GmABCG5 retarded the growth of soybean hairy roots, independent of nutrient iron conditions, confirming the growth-promotion function of GmABCG5. Iron deficiency has a negative effect on the growth of soybean complexes, which was more obvious in the GmABCG5 inhibition complexes. The chlorophyll content was increased in the GmABCG5 overexpression complexes and decreased in the GmABCG5 inhibition complexes. Iron deficiency treatment widened the gap in the chlorophyll contents. FCR activity was induced by iron deficiency and showed an extraordinary increase in the GmABCG5 overexpression complexes, accompanied by the greatest Fe accumulation. Antioxidant capacity was enhanced when GmABCG5 was overexpressed and reduced when GmABCG5 was inhibited under iron deficiency. These results showed that the response mechanism to iron deficiency is more actively mobilized in GmABCG5 overexpression seedlings. Our results indicated that GmABCG5 could improve the plant's tolerance to iron deficiency, suggesting that GmABCG5 might have the function of Fe mobilization, redistribution, and/or secretion of Fe substances in plants. The findings provide new insights into the ABCG subfamily genes in the regulation of iron homeostasis in plants.

Methyl viologen-induced changes in the Arabidopsis proteome implicate PATELLIN 4 in oxidative stress responses

The photosynthesis-induced accumulation of reactive oxygen species in chloroplasts can lead to oxidative stress, triggering changes in protein synthesis, degradation, and the assembly/disassembly of protein complexes. Using shot-gun proteomics, we identified methyl viologen-induced changes in protein abundance in wild-type Arabidopsis and oxidative stress-hypersensitive fsd1-1 and fsd1-2 knockout mutants, which are deficient in IRON SUPEROXIDE DISMUTASE 1 (FSD1). The levels of proteins that are localized in chloroplasts and the cytoplasm were modified in all lines treated with methyl viologen. Compared with the wild-type, fsd1 mutants showed significant changes in metabolic protein and chloroplast chaperone levels, together with increased ratio of cytoplasmic, peroxisomal, and mitochondrial proteins. Different responses in proteins involved in the disassembly of photosystem II-light harvesting chlorophyll a/b binding proteins were observed. Moreover, the abundance of PATELLIN 4, a phospholipid-binding protein enriched in stomatal lineage, was decreased in response to methyl viologen. Reverse genetic studies using patl4 knockout mutants and a PATELLIN 4 complemented line indicate that PATELLIN 4 affects plant responses to oxidative stress by effects on stomatal closure.

Multilayered regulation of iron homeostasis in Arabidopsis

Iron (Fe) is an essential micronutrient for plant growth and development due to its role in crucial processes such as photosynthesis and modulation of the redox state as an electron donor. While Fe is one of the five most abundant metals in the Earth's crust, it is poorly accessible to plants in alkaline soils due to the formation of insoluble complexes. To limit Fe deficiency symptoms, plant have developed a highly sophisticated regulation network including Fe sensing, transcriptional regulation of Fe-deficiency responsive genes, and post-translational modifications of Fe transporters. In this mini-review, we detail how plants perceive intracellular Fe status and how they regulate transporters involved in Fe uptake through a complex cascade of transcription factors. We also describe the current knowledge about intracellular trafficking, including secretion to the plasma membrane, endocytosis, recycling, and degradation of the two main Fe transporters, IRON-REGULATED TRANSPORTER 1 (IRT1) and NATURAL RESISTANCE ASSOCIATED MACROPHAGE PROTEIN 1 (NRAMP1). Regulation of these transporters by their non-Fe substrates is discussed in relation to their functional role to avoid accumulation of these toxic metals during Fe limitation.

Role of the plant-specific calcium-binding C2-DOMAIN ABSCISIC ACID-RELATED (CAR) protein family in environmental signaling

Many signaling processes rely on information decoding at the plasma membrane, and membrane-associated proteins and their complexes are fundamental for regulating this process. Still many questions exist as to how protein complexes are assembled and function at membrane sites to change identity and dynamics of membrane systems. Peripheral membrane proteins containing a calcium and phospholipid-binding C2-domain can act in membrane-related signaling by providing a tethering function so that protein complexes form. C2 domain proteins termed C2-DOMAIN ABSCISIC ACID-RELATED (CAR) proteins are plant-specific, and the functional relevance of this C2 domain protein subgroup is just emerging. The ten Arabidopsis CAR proteins CAR1 to CAR10 have a single C2 domain with a plant-specific insertion, the so-called "CAR-extra-signature" or also termed "sig domain". Via this "sig domain" CAR proteins can bind signaling protein complexes of different kinds and act in biotic and abiotic stress, blue light and iron nutrition. Interestingly, CAR proteins can oligomerize in membrane microdomains, and their presence in the nucleus can be linked with nuclear protein regulation. This shows that CAR proteins may play unprecedented roles in coordinating environmental responses and assembling required protein complexes to transmit information cues between plasma membrane and nucleus. The aim of this review is to summarize structure-function characteristics of the CAR protein family and assemble findings from CAR protein interactions and physiological functions. From this comparative investigation we extract common principles about the molecular operations that CAR proteins may fulfill in the cell. We also deduce functional properties of the CAR protein family based on its evolution and gene expression profiles. We highlight open questions and suggest novel avenues to prove and understand the functional networks and roles played by this protein family in plants.

Role of SEC14-like phosphatidylinositol transfer proteins in membrane identity and dynamics

Membrane identity and dynamic processes, that act at membrane sites, provide important cues for regulating transport, signal transduction and communication across membranes. There are still numerous open questions as to how membrane identity changes and the dynamic processes acting at the surface of membranes are regulated in diverse eukaryotes in particular plants and which roles are being played by protein interaction complexes composed of peripheral and integral membrane proteins. One class of peripheral membrane proteins conserved across eukaryotes comprises the SEC14-like phosphatidylinositol transfer proteins (SEC14L-PITPs). These proteins share a SEC14 domain that contributes to membrane identity and fulfills regulatory functions in membrane trafficking by its ability to sense, bind, transport and exchange lipophilic substances between membranes, such as phosphoinositides and diverse other lipophilic substances. SEC14L-PITPs can occur as single-domain SEC14-only proteins in all investigated organisms or with a modular domain structure as multi-domain proteins in animals and streptophytes (comprising charales and land plants). Here, we present an overview on the functional roles of SEC14L-PITPs, with a special focus on the multi-domain SEC14L-PITPs of the SEC14-nodulin and SEC14-GOLD group (PATELLINs, PATLs in plants). This indicates that SEC14L-PITPs play diverse roles from membrane trafficking to organism fitness in plants. We concentrate on the structure of SEC14L-PITPs, their ability to not only bind phospholipids but also other lipophilic ligands, and their ability to regulate complex cellular responses through interacting with proteins at membrane sites.