Iron is an essential element for most organisms. Both plants and microorganisms have developed different mechanisms for iron uptake, transport and storage. In the symbiosis systems, such as rhizobia–legume symbiosis and arbuscular mycorrhizal (AM) symbiosis, maintaining iron homeostasis to meet the requirements for the interaction between the host plants and the symbiotic microbes is a new challenge. This intriguing topic has drawn the attention of many botanists and microbiologists, and many discoveries have been achieved so far. In this review, we discuss the current progress on iron uptake and transport in the nodules and iron homeostasis in rhizobia–legume symbiosis. The discoveries with regard to iron uptake in AM fungi, iron uptake regulation in AM plants and interactions between iron and other nutrient elements during AM symbiosis are also summarized. At the end of this review, we propose prospects for future studies in this fascinating research area.
Abstract The differentiation of stomata provides a convenient model for studying pattern formation in plant tissues. Stomata formation is induced by a set of basic helix-loop-helix transcription factors and inhibited by a signal transduction pathway initiated by TOO MANY MOUTHS (TMM) and ERECTA family (ERf) receptors. The formation of a proper stomata pattern is also dependent upon the restriction of symplastic movement of basic helix-loop-helix transcription factors into neighboring cells, especially in the backgrounds where the function of the TMM/ERf signaling pathway is compromised. Here, we describe a novel mutant of KOBITO1 in Arabidopsis (Arabidopsis thaliana). The kob1-3 mutation leads to the formation of stomata clusters in the erl1 erl2 background but not in the wild type. Cell-to-cell mobility assays demonstrated an increase in intercellular protein trafficking in kob1-3, including increased diffusion of SPEECHLESS, suggesting that the formation of stomata clusters is due to an escape of cell fate-specifying factors from stomatal lineage cells. While plasmodesmatal permeability is increased in kob1-3, we did not detect drastic changes in callose accumulation at the neck regions of the plasmodesmata. Previously, KOBITO1 has been proposed to function in cellulose biosynthesis. Our data demonstrate that disruption of cellulose biosynthesis in the erl1 erl2 background does not lead to the formation of stomata clusters, indicating that cellulose biosynthesis is not a major determining factor for regulating plasmodesmatal permeability. Analysis of KOBITO1 structure suggests that it is a glycosyltransferase-like protein. KOBITO1 might be involved in a carbohydrate metabolic pathway that is essential for both cellulose biosynthesis and the regulation of plasmodesmatal permeability.
Summary Bundle sheath ( BS ) cells form a single cell layer surrounding the vascular tissue in leaves. In C3 plants, photosynthesis occurs in both the BS and mesophyll cells, but the BS cells are the major sites of photosynthesis in C4 plants, whereas the mesophyll cells are only involved in CO 2 fixation. Because C4 plants are more efficient photosynthetically, introduction of the C4 mechanism into C3 plants is considered a key strategy to improve crop yield. One prerequisite for such C3‐to‐C4 engineering is the ability to manipulate the number and physiology of the BS cells, but the molecular basis of BS cell‐fate specification remains unclear. Here we report that mutations in three GRAS family transcription factors, SHORT ‐ ROOT ( SHR ), SCARECROW ( SCR ) and SCARECROW ‐ LIKE 23 ( SCL 23), affect BS cell fate in A rabidopsis thaliana . SCR and SCL 23 are expressed specifically in the BS cells and act redundantly in BS cell‐fate specification, but their expression pattern and function diverge at later stages of leaf development. Using C h IP –chip experiments and sugar assays, we show that SCR is primarily involved in sugar transport whereas SCL 23 functions in mineral transport. SHR is also essential for BS cell‐fate specification, but it is expressed in the central vascular tissue. However, the SHR protein moves into the BS cells, where it directly regulates SCR and SCL 23 expression. SHR , SCR and SCL 23 homologs are present in many plant species, suggesting that this developmental pathway for BS cell‐fate specification is likely to be evolutionarily conserved.
Iron (Fe) is necessary for plant growth and development. Although it is well known that Fe deficiency causes chlorosis in plants, it remains unclear how the Fe homeostasis is regulated in mesophyll cells. The aim of this work was to identify a gene related to Fe homeostasis in leaves.A spontaneous mutant irm1, which revealed typical Fe-deficiency chlorosis, was found from Arabidopsis thaliana. Using map-based cloning, the gene responsible for the altered phenotype of irm1 was cloned. The expression of genes was analysed using northern blot hybridization and multiplex RT-PCR analysis. Further, GUS staining with transgenic promoter-GUS lines and transient expression of the fusion protein with GFP were used for detecting the expression pattern of the gene in different tissues and at different developmental stages, and for the subcelluar localization of the gene product.A point mutation from G to A at nucleotide 2317 of ClpC1 on chromosome V of Arabidopsis is responsible for the irm1 phenotype. The leaf chlorosis of the mutant irm1 and clpc1 (a T-DNA-inserted null mutant of ClpC1) could be converted to green by watering the soil with Fe solution. The expression intensity of ferric reductase FRO8 in irm1 and clpc1 was disordered (significantly higher than that of wild type).The glycine residue at amino acid 773 of ClpC1 is essential for its functions. In addition to its known functions reported previously, ClpC1 is involved in leaf Fe homeostasis, presumably via chloroplast translocation of some nuclear-encoded proteins which function in Fe transport.
Abstract Iron is an essential element for most organisms. As an indispensable co-factor of many enzymes, iron is involved in various crucial metabolic processes that are required for the survival of plants and pathogens. Conversely, excessive iron produces highly active reactive oxygen species, which are toxic to the cells of plants and pathogens. Therefore, plants and pathogens have evolved sophisticated mechanisms to modulate iron status at a moderate level for maintaining their fitness. Over the past decades, many efforts have been made to reveal these mechanisms, and some progress has been made. In this review, we describe recent advances in understanding the roles of iron in plant–pathogen interactions and propose prospects for future studies.
Tropical areas have a large distribution of saline soils and tidal flats with a high salinity level. Salinity stress is a key factor limiting the widespread use of tropical forage such as Stylosanthes guianensis (Aubl.) Sw. This study was designed to screen the salinity tolerance of 84 S. guianensis accessions; In a greenhouse experiment, plants were subjected to Hoagland solution or Hoagland solution with 200 mM NaCl for up to 15 days. Salinity tolerant accession CIAT11365 and salinity sensitive accession FM05-2 were obtained based on withered leaf rate (WLR). Further verification of salinity tolerance in CIAT11365 and FM05-2 with different salinity gradients showed that salinity stress increased WLR and decreased relative chlorophyll content (SPAD), maximum photochemical efficiency of photosystem II (Fv/Fm), and photosynthetic rate (Pn) in FM05-2, but CIAT11365 exhibited lower WLR and higher SPAD, Fv/Fm, and Pn. Leaf RNA-Seq revealed that Ca 2+ signal transduction and Na + transport ability, salinity tolerance-related transcription factors and antioxidant ability, an increase of auxin, and inhibition of cytokinin may play key roles in CIAT11365 response to salinity stress. The results of this study may contribute to our understanding of the molecular mechanism underlying the responses of S. guianensis to salinity stress and also provide important clues for further study and in-depth characterization of salinity resistance breeding candidate genes in S. guianensis .
Plants can be simultaneously exposed to multiple stresses. The interplay of abiotic and biotic stresses may result in synergistic or antagonistic effects on plant development and health. Temporary drought stress can stimulate plant immunity; however, the molecular mechanism of drought-induced immunity is largely unknown. In this study, we demonstrate that cysteine protease RD21A is required for drought-induced immunity. Temporarily drought-treated wild-type Arabidopsis plants became more sensitive to the bacterial pathogen-associated molecular pattern flg22, triggering stomatal closure, which resulted in increased resistance to Pseudomonas syringae pv. tomato DC3000 (Pst-DC3000). Knocking out rd21a inhibited flg22-triggered stomatal closure and compromised the drought-induced immunity. Ubiquitin E3 ligase SINAT4 interacted with RD21A and promoted its degradation in vivo. The overexpression of SINAT4 also consistently compromised the drought-induced immunity to Pst-DC3000. A bacterial type III effector, AvrRxo1, interacted with both SINAT4 and RD21A, enhancing SINAT4 activity and promoting the degradation of RD21A in vivo. Therefore, RD21A could be a positive regulator of drought-induced immunity, which could be targeted by pathogen virulence effectors during pathogenesis.
Author(s): Wu, Huilan; Du, Juan; Kong, Danyu; Ling, Hong-Qing | Abstract: Iron (Fe) is an essential mineral for plant growth and development. It plays crucial roles in many fundamental processes in cells, such as respiration, photosynthesis. In plant cells, iron is compartmentalized into different organelles, such as chloroplasts, mitochondria and vacuoles for its synthetic functions or storage. Chloroplast, a photosynthetic apparatus, represents one of the organelles possessing the most iron-enriched biochemical reaction systems (photosystem I, photosystem II, cytochrome b6-f complex and ferredoxin) in the plant cell. However, little is to known about the iron metabolism in this organelle.The ATP-dependent Clp protease is widely distributed in bacteria, cyanobacteria, mitochondria and chloroplasts and plays an important role in protein import to chloroplast (literature). In plants, the ATP-dependent Clp protease in chloroplasts is encoded by a nucleus gene ClpC. It is imported into chloroplast and functions in control of chlorophyll b synthesis (Nakagawara et al., 2007). Here, we show that CipC is involved in the iron homeostasis in mesophyll cells. Lesion of ClpC caused leaf chlorosis and growth inhibition, and this phenotype can be rescued by supplying iron. Expression profile analysis showed that the lesion of ClpC significantly increased the expression of AtFRO8 in the leaf, indicating that ClpC might be indirectly involved in the control of the expression of AtFRO8, consequently effect on iron homeostasis in chloroplasts.
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