COLD1: a cold sensor in rice

The Molecular Mechanism of Cold-Stress Tolerance: Cold Responsive Genes and Their Mechanisms in Rice (Oryza sativa L.)

Rice (Oryza sativa L.) production is highly susceptible to temperature fluctuations, which can significantly reduce plant growth and development at different developmental stages, resulting in a dramatic loss of grain yield. Over the past century, substantial efforts have been undertaken to investigate the physiological, biochemical, and molecular mechanisms of cold stress tolerance in rice. This review aims to provide a comprehensive overview of the recent developments and trends in this field. We summarized the previous advancements and methodologies used for identifying cold-responsive genes and the molecular mechanisms of cold tolerance in rice. Integration of new technologies has significantly improved studies in this era, facilitating the identification of essential genes, QTLs, and molecular modules in rice. These findings have accelerated the molecular breeding of cold-resistant rice varieties. In addition, functional genomics, including the investigation of natural variations in alleles and artificially developed mutants, is emerging as an exciting new approach to investigating cold tolerance. Looking ahead, it is imperative for scientists to evaluate the collective impacts of these novel genes to develop rice cultivars resilient to global climate change.

A comprehensive investigation of the regulatory roles of OsERF096, an AP2/ERF transcription factor, in rice cold stress response

KEY MESSAGE

OsERF096 negatively regulates rice cold tolerance and mediates IAA biosynthesis and signaling under cold stress. The APETALA2/ethylene-responsive factor (AP2/ERF) transcription factors play important roles in regulating plant tolerance to abiotic stress. OsERF096 was previously identified as a direct target of miR1320, and was suggested to negatively regulate rice cold tolerance. In this study, we performed RNA-sequencing and targeted metabolomics assays to reveal the regulatory roles of OsERF096 in cold stress response. GO and KEGG analysis of differentially expressed genes showed that the starch and sucrose metabolism, plant-pathogen interaction, and plant hormone signal transduction pathways were significantly enriched. Quantification analysis confirmed a significant difference in sugar contents among WT and OsERF096 transgenic lines under cold treatment. Targeted metabolomics analysis uncovered that IAA accumulation and signaling were modified by OsERF096 in response to cold stress. Expectedly, qRT-PCR assays confirmed significant OsIAAs and OsARFs expression changes in OsERF096 transgenic lines. Finally, we identified three targets of OsERF096 based on RNA-seq, qRT-PCR, and dual-LUC assays. In summary, these results revealed the multiple regulatory roles of OsERF096 in cold stress response.

Chilling-induced phosphorylation of IPA1 by OsSAPK6 activates chilling tolerance responses in rice

Chilling is a major abiotic stress harming rice development and productivity. The C-REPEAT BINDING FACTOR (CBF)-dependent transcriptional regulatory pathway plays a central role in cold stress and acclimation in Arabidopsis. In rice, several genes have been reported in conferring chilling tolerance, however, the chilling signaling in rice remains largely unknown. Here, we report the chilling-induced OSMOTIC STRESS/ABA-ACTIVATED PROTEIN KINASE 6 (OsSAPK6)-IDEAL PLANT ARCHITECTURE 1 (IPA1)-OsCBF3 signal pathway in rice. Under chilling stress, OsSAPK6 could phosphorylate IPA1 and increase its stability. In turn, IPA1 could directly bind to the GTAC motif on the OsCBF3 promoter to elevate its expression. Genetic evidence showed that OsSAPK6, IPA1 and OsCBF3 were all positive regulators of rice chilling tolerance. The function of OsSAPK6 in chilling tolerance depended on IPA1, and overexpression of OsCBF3 could rescue the chilling-sensitive phenotype of ipa1 loss-of-function mutant. Moreover, the natural gain-of-function allele ipa1-2D could simultaneously enhance seedling chilling tolerance and increase grain yield. Taken together, our results revealed a chilling-induced OsSAPK6-IPA1-OsCBF signal cascade in rice, which shed new lights on chilling stress-tolerant rice breeding.

Roles of E3 Ubiquitin Ligases in Plant Responses to Abiotic Stresses

Plants are frequently exposed to a variety of abiotic stresses, such as those caused by salt, drought, cold, and heat. All of these stressors can induce changes in the proteoforms, which make up the proteome of an organism. Of the many different proteoforms, protein ubiquitination has attracted a lot of attention because it is widely involved in the process of protein degradation; thus regulates many plants molecular processes, such as hormone signal transduction, to resist external stresses. Ubiquitin ligases are crucial in substrate recognition during this ubiquitin modification process. In this review, the molecular mechanisms of plant responses to abiotic stresses from the perspective of ubiquitin ligases have been described. This information is critical for a better understanding of plant molecular responses to abiotic stresses.

Recent Advances in the Analysis of Cold Tolerance in Maize

Maize (Zea mays L.) is an annual grass that originated in tropical and subtropical regions of the New World. Maize is highly sensitive to cold stress during seed gemination and the seedling phase, which can lead to reductions in plant vigor and grain production. There are large differences in the morphological and physiological changes caused by cold stress among maize varieties. In general, cold tolerant varieties have a stronger ability to maintain such changes in traits related to seed germination, root phenotypes, and shoot photosynthesis. These morphological and physiological characteristics have been widely used to evaluate the cold tolerance of maize varieties in genetic analyses. In recent years, considerable progress has been made in elucidating the mechanisms of maize in response to cold tolerance. Several QTL, GWAS, and transcriptomic analyses have been conducted on various maize genotypes and populations that show large variations in cold tolerance, resulting in the discovery of hundreds of candidate cold regulation genes. Nevertheless, only a few candidate genes have been functionally characterized. In the present review, we summarize recent progress in molecular, physiological, genetic, and genomic analyses of cold tolerance in maize. We address the advantages of joint analyses that combine multiple genetic and genomic approaches to improve the accuracy of identifying cold regulated genes that can be further used in molecular breeding. We also discuss the involvement of long-distance signaling in plant cold tolerance. These novel insights will provide a better mechanistic understanding of cold tolerance in maize.

A Sugarcane G-Protein-Coupled Receptor, ShGPCR1, Confers Tolerance to Multiple Abiotic Stresses

Sugarcane (Saccharum spp.) is a prominent source of sugar and serves as bioenergy/biomass feedstock globally. Multiple biotic and abiotic stresses, including drought, salinity, and cold, adversely affect sugarcane yield. G-protein-coupled receptors (GPCRs) are components of G-protein-mediated signaling affecting plant growth, development, and stress responses. Here, we identified a GPCR-like protein (ShGPCR1) from sugarcane and energy cane (Saccharum spp. hybrids) and characterized its function in conferring tolerance to multiple abiotic stresses. ShGPCR1 protein sequence contained nine predicted transmembrane (TM) domains connected by four extracellular and four intracellular loops, which could interact with various ligands and heterotrimeric G proteins in the cells. ShGPCR1 sequence displayed other signature features of a GPCR, such as a putative guanidine triphosphate (GTP)-binding domain, as well as multiple myristoylation and protein phosphorylation sites, presumably important for its biochemical function. Expression of ShGPCR1 was upregulated by drought, salinity, and cold stresses. Subcellular imaging and calcium (Ca²⁺) measurements revealed that ShGPCR1 predominantly localized to the plasma membrane and enhanced intracellular Ca²⁺ levels in response to GTP, respectively. Furthermore, constitutive overexpression of ShGPCR1 in sugarcane conferred tolerance to the three stressors. The stress-tolerance phenotype of the transgenic lines corresponded with activation of multiple drought-, salinity-, and cold-stress marker genes, such as Saccharum spp. LATE EMBRYOGENESIS ABUNDANT, DEHYDRIN, DROUGHT RESPONSIVE 4, GALACTINOL SYNTHASE, ETHYLENE RESPONSIVE FACTOR 3, SALT OVERLY SENSITIVE 1, VACUOLAR Na+/H+ ANTIPORTER 1, NAM/ATAF1/2/CUC2, COLD RESPONSIVE FACTOR 2, and ALCOHOL DEHYDROGENASE 3. We suggest that ShGPCR1 plays a key role in conferring tolerance to multiple abiotic stresses, and the engineered lines may be useful to enhance sugarcane production in marginal environments with fewer resources.

C2H2 Zinc Finger Proteins: Master Regulators of Abiotic Stress Responses in Plants

Abiotic stresses such as drought and salinity are major environmental factors that limit crop yields. Unraveling the molecular mechanisms underlying abiotic stress resistance is crucial for improving crop performance and increasing productivity under adverse environmental conditions. Zinc finger proteins, comprising one of the largest transcription factor families, are known for their finger-like structure and their ability to bind Zn2+. Zinc finger proteins are categorized into nine subfamilies based on their conserved Cys and His motifs, including the Cys2/His2-type (C2H2), C3H, C3HC4, C2HC5, C4HC3, C2HC, C4, C6, and C8 subfamilies. Over the past two decades, much progress has been made in understanding the roles of C2H2 zinc finger proteins in plant growth, development, and stress signal transduction. In this review, we focus on recent progress in elucidating the structures, functions, and classifications of plant C2H2 zinc finger proteins and their roles in abiotic stress responses.

OsCIPK7 point-mutation leads to conformation and kinase-activity change for sensing cold response

Calcineurin B-like interacting protein kinases (CIPKs) play important roles via environmental stress. However, less is known how to sense the stress in molecular structure conformation level. Here, an OsCIPK7 mutant via TILLING procedure with a point mutation in the kinase domain showed increased chilling tolerance, which could be potentially used in the molecular breeding. We found that this point mutation of OsCIPK7 led to a conformational change in the activation loop of the kinase domain, subsequently with an increase of protein kinase activity, thus conferred an increased tolerance to chilling stress.

Cold signaling in plants: Insights into mechanisms and regulation

To survive under cold temperatures plants must be able to perceive a cold signal and transduce it into downstream components that induce appropriate defense mechanisms. In addition to inducing adaptive defenses, such as the production of osmotic factors to prevent freezing and the reprogramming of transcriptional pathways, cold temperatures induce changes in plant growth and development which can affect the plant life cycle. In this review, we summarize recent progress in characterizing cold-related genes and the pathways that allow transduction of the cold signal in plants, focusing primarily on studies in Arabidopsis thaliana and rice (Oryza sativa). We summarize cold perception and signal transduction from the plasma membrane to the nucleus, which involves cold sensors, calcium signals, calcium-binding proteins, mitogen-activated protein kinase cascades, and the C-repeat binding factor/dehydration-responsive element binding pathways, as well as trehalose metabolism. Finally, we describe the balance between plant organogenesis and cold tolerance mechanisms in rice. This review encapsulates the known cold signaling factors in plants and provides perspectives for ongoing cold signaling research.

OsMADS57 together with OsTB1 coordinates transcription of its target OsWRKY94 and D14 to switch its organogenesis to defense for cold adaptation in rice

Plants modify their development to adapt to their environment, protecting themselves from detrimental conditions such as chilling stress by triggering a variety of signaling pathways; however, little is known about how plants coordinate developmental patterns and stress responses at the molecular level. Here, we demonstrate that interacting transcription factors OsMADS57 and OsTB1 directly target the defense gene OsWRKY94 and the organogenesis gene D14 to trade off the functions controlling/moderating rice tolerance to cold. Overexpression of OsMADS57 maintains rice tiller growth under chilling stress. OsMADS57 binds directly to the promoter of OsWRKY94, activating its transcription for the cold stress response, while suppressing its activity under normal temperatures. In addition, OsWRKY94 was directly targeted and suppressed by OsTB1 under both normal and chilling temperatures. However, D14 transcription was directly promoted by OsMADS57 for suppressing tillering under the chilling treatment, whereas D14 was repressed for enhancing tillering under normal condition.We demonstrated that OsMADS57 and OsTB1 conversely affect rice chilling tolerance via targeting OsWRKY94. Our findings highlight a molecular genetic mechanism coordinating organogenesis and chilling tolerance in rice, which supports and extends recent work suggesting that chilling stress environments influence organ differentiation.