Role of cassava CC-type glutaredoxin MeGRXC3 in regulating sensitivity to mannitol-induced osmotic stress dependent on its nuclear activity

Maize SERRATE 1B positively regulates seed germinability under low-temperature

Low temperature poses a significant threat to seedling emergence after maize sowing. While the impact of SERRATE (SE) on plant development via RNA processing has been extensively reported, its involvement in transcriptional regulation or the formation of low-temperature germination ability remains unclear. Our previous research revealed that ZmSE1B is located at the overlapping region of qLTGR4-1 or qLTPRL4-1, which has been associated with low-temperature germination by QTL analysis using IBM Syn4 RIL population. In the present study, we observed that maize seeds overexpressing ZmSE1B exhibited enhanced germination percentages, longer roots, and longer shoots when subjected to low-temperature conditions compared to the wildtype. Through an integrated analysis of RNA-Seq and CUT&Tag, we speculated that ZmGRXCC17, which encodes a GLUTAREDOXIN, may be upregulated by ZmSE1B in maize germinated seeds at low-temperature. Further, the regulation of ZmSE1B on transcription of ZmGRXCC17 was validated using dual-luciferase reporter system and CUT&Tag-qPCR. Finally, the positive effect of ZmGRXCC17 on low-temperature tolerance during seed germination was elucidated through its heterologous expression in rice. The results indicate that ZmSE1B enhances the seed germination ability under low temperature by regulating the transcription of ZmGRXCC17.

Sexual reproduction in land plants: an evolutionary perspective

KEY MESSAGE

We link key aspects of land plant reproductive evolution and detail how successive molecular changes leading to novel tissues and organs require co-evolution of communication systems between tissues. The transition of water-dependent reproduction of algae to mechanisms with very limited water dependence in many land plant lineages allowed plants to colonize diverse terrestrial environments, leading to the vast variety of extant plant species. The emergence of modified cell types, novel tissues, and organs enabled this transition; their origin is associated with the co-evolution of novel or adapted molecular communication systems and gene regulatory networks. In the light of an increasing number of genome sequences in combination with the establishment of novel genetic model organisms from diverse green plant lineages, our knowledge and understanding about the origin and evolution of individual traits that arose in a concerted way increases steadily. For example, novel members of gene families in signaling pathways emerged for communication between gametes and gametophytes with additional tissues surrounding the gametes. Here, we provide a comprehensive overview on the origin and evolution of reproductive novelties such as pollen grains, immobile sperms, ovules and seeds, carpels, gamete/gametophytic communication systems, double fertilization, and the molecular mechanisms that have arisen anew or have been co-opted during evolution, including but not limited to the incorporation of phytohormones, reactive oxygen species and redox signaling as well as small RNAs in regulatory modules that contributed to the evolution of land plant sexual reproduction.

An evolutionary view of the function of CC-type glutaredoxins in plant development and adaptation to the environment

Land plants have to face an oxidizing, heterogeneous, and fast changing environment. Redox-dependent post-translational modifications emerge as a critical component of plant responses to stresses. Among the thiol oxidoreductase superfamily, class III CC-type glutaredoxins (called ROXYs) are land plant specific, and their evolutionary history is highly dynamic. Angiosperms encode many isoforms, classified into five subgroups (Aα, Aβ, Bα, Bβ, Bγ) that probably evolved from five common ancestral ROXYs, with higher evolutionary dynamics in the Bγ subgroup compared with the other subgroups. ROXYs can modulate the transcriptional activity of TGA transcription factor target genes, although their biochemical function is still debated. ROXYs participate in the control of proper plant development and reproduction, and are mainly negative regulators of plant responses to biotic and abiotic stresses. This suggests that most ROXYs could play essential and conserved functions in resetting redox-dependent changes in transcriptional activity upon stress signaling to ensure the responsiveness of the system and/or avoid exaggerated responses that could lead to major defects in plant growth and reproduction. In Arabidopsis Bγ members acquired important functions in responses to nitrogen availability and endogenous status, but the rapid and independent evolution of this subclass might suggest that this function results from neofunctionalization, specifically observed in core eudicots.

Differential gene expression in irradiated potato tubers contributed to sprout inhibition and quality retention during a commercial scale storage

Current study is the first ever storage cum market trial of radiation processed (28 tons) of potato conducted in India at a commercial scale. The objective was to affirm the efficacy of very low dose of gamma radiation processing of potato for extended storage with retained quality and to understand the plausible mechanism at the gene modulation level for suppression of potato sprouting. Genes pertaining to abscisic acid (ABA) biosynthesis were upregulated whereas its catabolism was downregulated in irradiated potatoes. Additionally, genes related to auxin buildup were downregulated in irradiated potatoes. The change in the endogenous phytohormone contents in irradiated potato with respect to the control were found to be correlated well with the differential expression level of certain related genes. Irradiated potatoes showed retention of processing attributes including cooking and chip-making qualities, which could be attributed to the elevated expression of invertase inhibitor in these tubers. Further, quality retention in radiation treated potatoes may also be related to inhibition in the physiological changes due to sprout inhibition. Ecological and economical analysis of national and global data showed that successful adoption of radiation processing may gradually replace sprout suppressants like isopropyl N-(3-chlorophenyl) carbamate (CIPC), known to leave residue in the commodity, stabilize the wholesale annual market price, and provide a boost to the industries involved in product manufacturing.

Capsicum chinense Jacq.-derived glutaredoxin (CcGRXS12) alters redox status of the cells to confer resistance against pepper mild mottle virus (PMMoV-I)

KEY MESSAGE

The CcGRXS12 gene protects plants from cellular oxidative damage that are caused by both biotic and abiotic stresses. The protein possesses GSH-disulphide oxidoreductase property but lacks Fe-S cluster assembly mechanism. Glutaredoxins (Grxs) are small, ubiquitous and multi-functional proteins. They are present in different compartments of plant cells. A chloroplast targeted Class I GRX (CcGRXS12) gene was isolated from Capsicum chinense during the pepper mild mottle virus (PMMoV) infection. Functional characterization of the gene was performed in Nicotiana benthamiana transgenic plants transformed with native C. chinense GRX (Nb:GRX), GRX-fused with GFP (Nb:GRX-GFP) and GRX-truncated for chloroplast sequences fused with GFP (Nb:Δ2MGRX-GFP). Overexpression of CcGRXS12 inhibited the PMMoV-I accumulation at the later stage of infection, accompanied with the activation of salicylic acid (SA) pathway pathogenesis-related (PR) transcripts and suppression of JA/ET pathway transcripts. Further, the reduced accumulation of auxin-induced Glutathione-S-Transferase (pCNT103) in CcGRXS12 overexpressing lines indicated that the protein could protect the plants from the oxidative stress caused by the virus. PMMoV-I infection increased the accumulation of pyridine nucleotides (PNs) mainly due to the reduced form of PNs (NAD(P)H), and it was high in Nb:GRX-GFP lines compared to other transgenic lines. Apart from biotic stress, CcGRXS12 protects the plants from abiotic stress conditions caused by H2O2 and herbicide paraquat. CcGRXS12 exhibited GSH-disulphide oxidoreductase activity in vitro; however, it was devoid of complementary Fe-S cluster assembly mechanism found in yeast. Overall, this study proves that CcGRXS12 plays a crucial role during biotic and abiotic stress in plants.

Molecular identification and functional characterization of an environmental stress responsive glutaredoxin gene ROXY1 in Quercus glauca

Quercus glauca is a valuable natural resource with both economic and ecological values. It is one of the dominant forest tree species widely distributed in Southern China. As a perennial broadleaf plant, Q. glauca inevitably encounters numerous stresses from environment. Glutaredoxins (GRXs) are a kind of small oxidoreductases that play an important role in response to oxidative stress. CC-type GRXs also known as ROXYs are specific to land plants. In this study, we isolated a CC-type GRX gene, QgROXY1, from Q. glauca. Expression of QgROXY1 is induced by a variety of environmental stimuli. QgROXY1 protein localizes to both cytoplasm and nucleus; whereas the nucleus localized QgROXY1 could physically interact with the basic region/leucine zipper motif (bZIP) transcription factor AtTGA2 from Arabidopsis thaliana. Transgenic A. thaliana ectopically expressing QgROXY1 is hypersensitive to exogenously applied salicylic acid. Induction of plant defense gene is significantly impaired in QgROXY1 transgenic plants that results in enhanced susceptibility to infection of Botrytis cinerea pathogen, indicating the evolutionary conserved function among ROXY homologs in weedy and woody plants. This is the first described function for the ROXYs in tree plants. Through this case study, we demonstrated the feasibility and efficacy of molecular technology applied to characterization of gene function in tree species.

Redox regulation, thioredoxins, and glutaredoxins in retrograde signalling and gene transcription

Integration of reactive oxygen species (ROS)-mediated signal transduction pathways via redox sensors and the thiol-dependent signalling network is of increasing interest in cell biology for their implications in plant growth and productivity. Redox regulation is an important point of control in protein structure, interactions, cellular location, and function, with thioredoxins (TRXs) and glutaredoxins (GRXs) being key players in the maintenance of cellular redox homeostasis. The crosstalk between second messengers, ROS, thiol redox signalling, and redox homeostasis-related genes controls almost every aspect of plant development and stress response. We review the emerging roles of TRXs and GRXs in redox-regulated processes interacting with other cell signalling systems such as organellar retrograde communication and gene expression, especially in plants during their development and under stressful environments. This approach will cast light on the specific role of these proteins as redox signalling components, and their importance in different developmental processes during abiotic stress.

CC-type glutaredoxin, MeGRXC3, associates with catalases and negatively regulates drought tolerance in cassava (Manihot esculenta Crantz)

Glutaredoxins (GRXs) are essential for reactive oxygen species (ROS) homeostasis in responses of plants to environment changes. We previously identified several drought-responsive CC-type GRXs in cassava, an important tropical crop. However, how CC-type GRX regulates ROS homeostasis of cassava under drought stress remained largely unknown. Here, we report that a drought-responsive CC-type GRX, namely MeGRXC3, was associated with activity of catalase in the leaves of 100 cultivars (or unique unnamed genotypes) of cassava under drought stress. MeGRXC3 negatively regulated drought tolerance by modulating drought- and abscisic acid-induced stomatal closure in transgenic cassava. It antagonistically regulated hydrogen peroxide (H₂ O₂ ) accumulation in epidermal cells and guard cells. Moreover, MeGRXC3 interacted with two catalases of cassava, MeCAT1 and MeCAT2, and regulated their activity in vivo. Additionally, MeGRXC3 interacts with a cassava TGA transcription factor, MeTGA2, in the nucleus, and regulates the expression of MeCAT7 through a MeTGA2-MeMYB63 pathway. Overall, we demonstrated the roles of MeGRXC3 in regulating activity of catalase at both transcriptional and post-translational levels, therefore involving in ROS homeostasis and stomatal movement in responses of cassava to drought stress. Our study provides the first insights into how MeGRXC3 may be used in molecular breeding of cassava crops.