Functional characterization of rice metallothionein OsMT-I-Id: Insights into metal binding and heavy metal tolerance mechanisms.

Metallothioneins (MTs) are cysteine-rich proteins known for their strong metal-binding capabilities, making them effective in detoxifying heavy metals (HMs). This study focuses on characterizing the functional properties of OsMT-I-Id, a type-I Metallothionein found in rice. Using a HM-responsive yeast cup1Δ (DTY4), ycf1∆ (for cadmium), and acr3∆ mutants (for trivalent arsenic), we assessed the impact of OsMT-I-Id on metal accumulation and cellular resilience. Our results demonstrated that yeast cells expressing OsMT-I-Id showed increased tolerance and accumulated higher levels of copper (Cu), arsenic (As), and cadmium (Cd), compared to control cells. This can be attributed to the protein's ability to chelate and bind HMs. Site-directed mutagenesis was employed to investigate the specific contributions of cysteine residues. The study revealed that yeast cells with a mutated C-domain displayed heightened HM sensitivity, while cells with a mutated N-domain exhibited reduced sensitivity. This underscores the critical role of C-cysteine-rich domains in metal binding and tolerance of type-I rice MTs. Furthermore, the study identified the significance of the 12th cysteine position at the N-domain and the 68th and 72nd cysteine positions at the C-domain in influencing OsMT-I-Id metal-binding capacity. This research provides novel insights into the structure-function relationship and metal binding properties of type-I plant MTs.

Phytoremediation potential of Solanum viarum Dunal and functional aspects of their capitate glandular trichomes in lead, cadmium, and zinc detoxification.

In the present scenario, remediation of heavy metals (HMs) contaminated soil has become an important work to be done for the well-being of human and their environment. Phytoremediation can be regarded as an excellent method in environmental technologies. The present contemporary research explores the Solanum viarum Dunal function as a potential accumulator of hazardous HMs viz. lead (Pb), cadmium (Cd), zinc (Zn), and their combination (CHM). On toxic concentrations of Pb, Cd, Zn, and their synergistic exposure, seeds had better germination percentage and their 90d old aerial tissues accumulated Pb, Cd, and Zn concentrations ranging from 44.53, 84.06, and 147.29 mg kg-1 DW, respectively. Pattern of accumulation in roots was as Zn 70.08 > Pb 48.55 > Cd 42.21 mg kg-1DW. Under HMs treatment, positive modulation in physiological performances, antioxidant activities suggested an enhanced tolerance along with higher membrane stability due to increased levels of lignin, proline, and sugar. Phenotypic variations were recorded in prickles and roots of 120 d old HM stressed plants, which are directly correlated with better acclimation. Interestingly, trichomes of the plant also showed HM accumulation. Later, SEM-EDX microanalysis suggested involvement of S. viarum capitate glandular trichomes as excretory organs for Cd and Zn. Thus, the present study provides an understanding of the mechanism that makes S. viarum to function as potent accumulator and provides information to generate plants to be used for phytoremediation.

Species-specific transcriptional reprogramming during adventitious root initiation.

Adventitious roots or shoot-borne roots transdifferentiate from cells close to vascular tissues after cell reprogramming, which is associated with increased transcriptional activity. Recently, Garg et al. provided a genome-wide landscape of transcriptional signatures during the early stages of adventitious root initiation in rice and showed that conserved transcription factors acquire species-specific function.

A tau class GST, OsGSTU5, interacts with VirE2 and modulates the Agrobacterium-mediated transformation in rice.

KEY MESSAGE: OsGSTU5 interacts and glutathionylates the VirE2 protein of Agrobacterium and its (OsGSTU5) overexpression and downregulation showed a low and high AMT efficiency in rice, respectively. During Agrobacterium-mediated transformation (AMT), T-DNA along with several virulence proteins such as VirD2, VirE2, VirE3, VirD5, and VirF enter the plant cytoplasm. VirE2 serves as a single-stranded DNA binding (SSB) protein that assists the cytoplasmic trafficking of T-DNA inside the host cell. Though the regulatory roles of VirE2 have been established, the cellular reaction of their host, especially in monocots, has not been characterized in detail. This study identified a cellular interactor of VirE2 from the cDNA library of rice. The identified plant protein encoded by the gene cloned from rice was designated OsGSTU5, it interacted specifically with VirE2 in the host cytoplasm. OsGSTU5 was upregulated during Agrobacterium infection and involved in the post-translational glutathionylation of VirE2 (gVirE2). Interestingly, the in silico analysis showed that the 'gVirE2 + ssDNA' complex was structurally less stable than the 'VirE2 + ssDNA' complex. The gel shift assay also confirmed the attenuated SSB property of gVirE2 over VirE2. Moreover, knock-down and overexpression of OsGSTU5 in rice showed increased and decreased T-DNA expression, respectively after Agrobacterium infection. The present finding establishes the role of OsGSTU5 as an important target for modulation of AMT efficiency in rice.

A tau class glutathione-S-transferase (OsGSTU5) confers tolerance against arsenic toxicity in rice by accumulating more arsenic in root.

Arsenic (As) considered as one of the hazardous metalloid that hampers various physiological activities in rice. To study the mechanism of As tolerance in rice, one differentially expressed tau class glutathione-S-transferase (OsGSTU5) has been selected and transgenic rice plants with knockdown (KD) and overexpressing (OE) OsGSTU5 were generated. Our results suggested that KD lines became less tolerant to As stress than WT plants, while OE lines showed enhanced tolerance to As. Under As toxicity, OE and KD lines showed enhanced and reduced antioxidant activities such as, SOD, PRX and catalase, respectively indicating its role in ROS homeostasis. In addition, higher malondialdehyde content, poor photosynthetic parameters and higher reactive oxygen species (ROS) in KD plant, suggests that knockdown of OsGSTU5 renders KD plants more susceptible to oxidative damage. Also, the relative expression profile of various transporters such as OsABCC1 (As sequestration), Lsi2 and Lsi6 (As translocaters) and GSH dependent activity of GSTU5 suggests that GSTU5 might help in chelation of As with GSH and sequester it into the root vacuole using OsABCC1 transporter and thus limits the upward translocation of As towards shoot. This study suggests the importance of GSTU5 as a good target to improve the As tolerance in rice.

Class III peroxidase: an indispensable enzyme for biotic/abiotic stress tolerance and a potent candidate for crop improvement.

Class III peroxidases are secretory enzymes which belong to a ubiquitous multigene family in higher plants and have been identified to play role in a broad range of physiological and developmental processes. Potentially, it is involved in generation and detoxification of hydrogen peroxide (H2O2), and their subcellular localization reflects through three different cycles, namely peroxidative cycle, oxidative and hydroxylic cycles to maintain the ROS level inside the cell. Being an antioxidant, class III peroxidases are an important initial defence adapted by plants to cope with biotic and abiotic stresses. Both these stresses have become a major concern in the field of agriculture due to their devastating effect on plant growth and development. Despite numerous studies on plant defence against both the stresses, only a handful role of class III peroxidases have been uncovered by its functional characterization. This review will cover our current understanding on class III peroxidases and the signalling involved in their regulation under both types of stresses. The review will give a view of class III peroxidases and highlights their indispensable role under stress conditions. Its future application will be discussed to showcase their importance in crop improvement by genetic manipulation and by transcriptome analysis.

Recent advances in arsenic metabolism in plants: current status, challenges and highlighted biotechnological intervention to reduce grain arsenic in rice.

Arsenic (As), classified as a "metalloid" element, is well known for its carcinogenicity and other toxic effects to humans. Arsenic exposure in plants results in the alteration of the physiochemical and biological properties and consequently, loss of crop yield. Being a staple food for half of the world's population, the consumption of As-contaminated rice grain by humans may pose serious health issues and risks for food security. In this study, we have described the principal understanding of the molecular basis of arsenic toxicity and accumulation in plant parts. We described the measures for decreasing As accumulation in rice and understanding the mechanism and transport of As uptake, its transport from root to shoot to rice grain, its metabolism, detoxification, as well as the mechanisms lying behind its accumulation in rice grains. There are various checkpoints, such as the tuning of AsV/Pi specific Pi transporters, arsenate reductase, transporters that are involved in the efflux of As to either the vacuole or outside the cell, xylem loading, loading and unloading to the phloem, and transporters involved in the loading of As to grain, that can be targeted to reduce As accumulation in rice grain. Genes/proteins involved in As detoxification, particularly the glutathione (GSH) biosynthesis pathway, phytochelatin (PC) synthesis, and arsenic methyltransferase, also provide a great pool of pathways that can also be castellated for the low As in rice grains. Paddy rice is also used as fodder for animals, enhancing vacuolar sequestration and using constitutive promoters, which may be of concern for animal health. Therefore, using a root-specific promoter and/or converting inorganic arsenic into volatile organic arsenic might be a better strategy for low As in grain. Furthermore, in this review, the other specific approaches, such as bio-remediation, bio-augmentation practices, and molecular breeding, which have great potential to reduce As uptake from soil to rice grains, have also been highlighted.

Oryza sativa class III peroxidase (OsPRX38) overexpression in Arabidopsis thaliana reduces arsenic accumulation due to apoplastic lignification.

ClassIII peroxidases are multigene family of plant-specific peroxidase enzyme. They are involved in various physiological and developmental processes like auxin catabolism, cell metabolism, various biotic, abiotic stresses and cell elongation. In the present study, we identified a class III peroxidase (OsPRX38) from rice which is upregulated several folds in both arsenate (AsV) and arsenite (AsIII) stresses. The overexpression of OsPRX38 in Arabidopsis thaliana significantly enhances Arsenic (As) tolerance by increasing SOD, PRX GST activity and exhibited low H2O2, electrolyte leakage and malondialdehyde content. OsPRX38 overexpression also affect the plant growth by increasing total biomass and seeds production in transgenics than WT under As stress condition. Confocal microscopy revealed that the OsPRX38-YFP fusion protein was localized to the apoplast of the onion epidermal cells. In addition, lignification was positively correlated with an increase in cell-wall-associated peroxidase activities in transgenic plants. This study indicates the role of OsPRX38 in lignin biosynthesis, where lignin act as an apoplastic barrier for As entry in root cells leading to reduction of As accumulation in transgenic. Overall the study suggests that overexpression of OsPRX38 in Arabidopsis thaliana activates the signaling network of different antioxidant systems under As stress condition, enhancing the plant tolerance by reducing As accumulation due to high lignification.

Genome-wide analysis of rice dehydrin gene family: Its evolutionary conservedness and expression pattern in response to PEG induced dehydration stress.

Abiotic stresses adversely affect cellular homeostasis, impairing overall growth and development of plants. These initial stress signals activate downstream signalling processes, which, subsequently, activate stress-responsive mechanisms to re-establish homeostasis. Dehydrins (DHNs) play an important role in combating dehydration stress. Rice (Oryza sativa L.), which is a paddy crop, is susceptible to drought stress. As drought survival in rice might be viewed as a trait with strong evolutionary selection pressure, we observed DHNs in the light of domestication during the course of evolution. Overall, 65 DHNs were identified by a genome-wide survey of 11 rice species, and 3 DHNs were found to be highly conserved. The correlation of a conserved pattern of DHNs with domestication and diversification of wild to cultivated rice was validated by synonymous substitution rates, indicating that Oryza rufipogon and Oryza sativa ssp. japonica follow an adaptive evolutionary pattern; whereas Oryza nivara and Oryza sativa ssp. indica demonstrate a conserved evolutionary pattern. A comprehensive analysis of tissue-specific expression of DHN genes in japonica and their expression profiles in normal and PEG (poly ethylene glycol)-induced dehydration stress exhibited a spatiotemporal expression pattern. Their interaction network reflects the cross-talk between gene expression and the physiological processes mediating adaptation to dehydration stress. The results obtained strongly indicated the importance of DHNs, as they are conserved during the course of domestication.