The Indeterminate Domain Protein ROC1 Regulates Chilling Tolerance via Activation of DREB1B/CBF1 in Rice

Advances and opportunities in unraveling cold-tolerance mechanisms in the world's primary staple food crops

Temperatures below or above optimal growth conditions are among the major stressors affecting productivity, end-use quality, and distribution of key staple crops including rice (Oryza sativa), wheat (Triticum aestivum), and maize (Zea mays L.). Among temperature stresses, cold stress induces cellular changes that cause oxidative stress and slowdown metabolism, limit growth, and ultimately reduce crop productivity. Perception of cold stress by plant cells leads to the activation of cold-responsive transcription factors and downstream genes, which ultimately impart cold tolerance. The response triggered in crops to cold stress includes gene expression/suppression, the accumulation of sugars upon chilling, and signaling molecules, among others. Much of the information on the effects of cold stress on perception, signal transduction, gene expression, and plant metabolism are available in the model plant Arabidopsis but somewhat lacking in major crops. Hence, a complete understanding of the molecular mechanisms by which staple crops respond to cold stress remain largely unknown. Here, we make an effort to elaborate on the molecular mechanisms employed in response to low-temperature stress. We summarize the effects of cold stress on the growth and development of these crops, the mechanism of cold perception, and the role of various sensors and transducers in cold signaling. We discuss the progress in cold tolerance research at the genome, transcriptome, proteome, and metabolome levels and highlight how these findings provide opportunities for designing cold-tolerant crops for the future.

Transcriptomic analysis of Cucumis sativus uncovers putative genes related to hormone signaling under low temperature (LT) and high humidity (HH) stress

Climate change has caused changes in environmental conditions, leading to both low temperature (LT) and high humidity (HH) stress on crops worldwide. Therefore, there is a growing need to enhance our understanding of the physiological and molecular mechanisms underlying LT and HH stress tolerance in cucumbers, given the significance of climate change. The findings of this study offer a comprehensive understanding of how the transcriptome and hormone profiles of cucumbers respond to LT and HH stress. In this study, cucumber seedlings were subjected to LT and HH stress (9/5 °C day/night temperature, 95% humidity) as well as control (CK) conditions (25/18 °C day/night temperature, 80% humidity) for 24, 48, and 72 h. It was observed that the LT and HH stress caused severe damage to the morphometric traits of the plants compared to the control treatment. The concentrations of phytohormones IAA, ethylene, and GA were lower, while ABA and JA were higher during LT and HH stress at most time points. To gain insights into the molecular mechanisms underlying this stress response, RNA-sequencing was performed. The analysis revealed a total of 10,459 differentially expressed genes (DEGs) with annotated pathways. These pathways included plant hormone signal transduction, protein processing in the endoplasmic reticulum, MAPK signaling pathway, carbon fixation in photosynthetic organisms, and glycerolipid metabolism. Furthermore, 123 DEGs associated with hormone signaling pathways were identified, and their responses to LT and HH stress were thoroughly discussed. Overall, this study sheds light on the LT and HH tolerance mechanisms in cucumbers, particularly focusing on the genes involved in the LT and HH response and the signaling pathways of endogenous phytohormones.

Comprehensive Analysis of the INDETERMINATE DOMAIN (IDD) Gene Family and Their Response to Abiotic Stress in Zea mays

Transcription factors (TFs) are important regulators of numerous gene expressions due to their ability to recognize and combine cis-elements in the promoters of target genes. The INDETERMINATE DOMAIN (IDD) gene family belongs to a subfamily of C2H2 zinc finger proteins and has been identified only in terrestrial plants. Nevertheless, little study has been reported concerning the genome-wide analysis of the IDD gene family in maize. In total, 22 ZmIDD genes were identified, which can be distributed on 8 chromosomes in maize. On the basis of evolutionary relationships and conserved motif analysis, ZmIDDs were categorized into three clades (1, 2, and 3), each owning 4, 6, and 12 genes, respectively. We analyzed the characteristics of gene structure and found that 3 of the 22 ZmIDD genes do not contain an intron. Cis-element analysis of the ZmIDD promoter showed that most ZmIDD genes possessed at least one ABRE or MBS cis-element, and some ZmIDD genes owned the AuxRR-core, TCA-element, TC-rich repeats, and LTR cis-element. The Ka:Ks ratio of eight segmentally duplicated gene pairs demonstrated that the ZmIDD gene families had undergone a purifying selection. Then, the transcription levels of ZmIDDs were analyzed, and they showed great differences in diverse tissues as well as abiotic stresses. Furthermore, regulatory networks were constructed through the prediction of ZmIDD-targeted genes and miRNAs, which can inhibit the transcription of ZmIDDs. In total, 6 ZmIDDs and 22 miRNAs were discovered, which can target 180 genes and depress the expression of 9 ZmIDDs, respectively. Taken together, the results give us valuable information for studying the function of ZmIDDs involved in plant development and climate resilience in maize.

Genome-Wide Identification of the Highly Conserved INDETERMINATE DOMAIN (IDD) Zinc Finger Gene Family in Moso Bamboo (Phyllostachys edulis)

INDETERMINATE DOMAIN (IDD) proteins, a family of transcription factors unique to plants, function in multiple developmental processes. Although the IDD gene family has been identified in many plants, little is known about it in moso bamboo. In this present study, we identified 32 PheIDD family genes in moso bamboo and randomly sequenced the full-length open reading frames (ORFs) of ten PheIDDs. All PheIDDs shared a highly conserved IDD domain that contained two canonical C2H2-ZFs, two C2HC-ZFs, and a nuclear localization signal. Collinearity analysis showed that segmental duplication events played an important role in expansion of the PheIDD gene family. Synteny analysis indicated that 30 PheIDD genes were orthologous to those of rice (Oryza sativa). Thirty PheIDDs were expressed at low levels, and most PheIDDs exhibited characteristic organ-specific expression patterns. Despite their diverse expression patterns in response to exogenous plant hormones, 8 and 22 PheIDDs responded rapidly to IAA and 6-BA treatments, respectively. The expression levels of 23 PheIDDs were closely related to the outgrowth of aboveground branches and 20 PheIDDs were closely related to the awakening of underground dormant buds. In addition, we found that the PheIDD21 gene generated two products by alternative splicing. Both isoforms interacted with PheDELLA and PheSCL3. Furthermore, both isoforms could bind to the cis-elements of three genes (PH02Gene17121, PH02Gene35441, PH02Gene11386). Taken together, our work provides valuable information for studying the molecular breeding mechanism of lateral organ development in moso bamboo.

Malectin Domain Protein Kinase (MDPK) Promotes Rice Resistance to Sheath Blight via IDD12, IDD13, and IDD14

Sheath blight (ShB) caused by Rhizoctonia solani is a major disease of rice, seriously affecting yield; however, the molecular defense mechanism against ShB remains unclear. A previous transcriptome analysis of rice identified that R. solani inoculation significantly induced MDPK. Genetic studies using MDPK RNAi and overexpressing plants identified that MDPK positively regulates ShB resistance. This MDPK protein was found localized in the endoplasmic reticulum (ER) and Golgi apparatus. Yeast one-hybrid assay, electrophoresis mobility shift assay (EMSA), and chromatin immunoprecipitation (ChIP) showed that the intermediate domain proteins IDD12, IDD13, and IDD14 bind to the MDPK promoter. Moreover, IDD14 was found to interact with IDD12 and IDD13 to form a transcription complex to activate MDPK expression. The three IDDs demonstrated an additive effect on MDPK activation. Further genetic studies showed that the IDD13 and IDD14 single mutants were more susceptible to ShB but not IDD12, while IDD12, IDD13, and IDD14 overexpressing plants were less susceptible than the wild-type plants. The IDD12, IDD13, and IDD14 mutants also proved the additive effect of the three IDDs on MDPK expression, which regulates ShB resistance in rice. Notably, MDPK overexpression maintained normal yield levels in rice. Thus, our study proves that IDD12, IDD13, and IDD14 activate MDPK to enhance ShB resistance in rice. These results improve our knowledge of rice defense mechanisms and provide a valuable marker for resistance breeding.

Convergence and Divergence: Signal Perception and Transduction Mechanisms of Cold Stress in Arabidopsis and Rice

Cold stress, including freezing stress and chilling stress, is one of the major environmental factors that limit the growth and productivity of plants. As a temperate dicot model plant species, Arabidopsis develops a capability to freezing tolerance through cold acclimation. The past decades have witnessed a deep understanding of mechanisms underlying cold stress signal perception, transduction, and freezing tolerance in Arabidopsis. In contrast, a monocot cereal model plant species derived from tropical and subtropical origins, rice, is very sensitive to chilling stress and has evolved a different mechanism for chilling stress signaling and response. In this review, the authors summarized the recent progress in our understanding of cold stress response mechanisms, highlighted the convergent and divergent mechanisms between Arabidopsis and rice plasma membrane cold stress perceptions, calcium signaling, phospholipid signaling, MAPK cascade signaling, ROS signaling, and ICE-CBF regulatory network, as well as light-regulated signal transduction system. Genetic engineering approaches of developing freezing tolerant Arabidopsis and chilling tolerant rice were also reviewed. Finally, the future perspective of cold stress signaling and tolerance in rice was proposed.

Comparative transcriptomic analysis reveals the cold acclimation during chilling stress in sensitive and resistant passion fruit (Passiflora edulis) cultivars

Chilling stress (CS) is an important limiting factor for the growth and development of passion fruit (Passiflora edulis) in winter in South China. However, little is known about how the passion fruit responds and adapts to CS. In this study, we performed transcriptome sequencing of cold-susceptible cultivar Huangjinguo (HJG) and cold-tolerant cultivar Tainong 1 (TN1) under normal temperature (NT) and CS conditions, and a total of 47,353 unigenes were obtained by seven databases. Using differentially expressed unigenes (DEGs) analysis, 3,248 and 4,340 DEGs were identified at two stages, respectively. The Gene Ontology (GO) enrichment analysis showed that the DEGs were mainly related to phosphorylation, membrane protein, and catalytic activity. In Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway, the unigenes of plant-pathogen interaction, plant hormone signal transduction and fatty acid metabolism were enriched. Then, the 12,471 filtered unigenes were clustered into eight co-expression modules, and two modules were correlated with CS. In this two modules, 32 hub unigenes were obtained. Furthermore, the unigenes related to CS were validated using quantitative real-time PCR (RT-qPCR). This work showed that the expression levels of CS-related unigenes were very different in two passion fruit cultivars. The results provide information for the development of passion fruit with increased chilling tolerance.

Indeterminate domain 3 negatively regulates plant erectness and the resistance of rice to sheath blight by controlling PIN-FORMED gene expressions

Plant architecture and disease resistance are the key factors that control the production of yield. However, the mechanism behind these factors is largely unknown. In this study, we identified that indeterminate domain 3 (IDD3) was obviously induced by inoculation of Rhizoctonia solani AG1-IA. Plants that overexpressed IDD3 (IDD3 OX) were more susceptible, while idd3 mutants showed a similar response to sheath blight disease compared with wild-type plants. Interestingly, IDD3 OX plants developed a wider tiller angle and exhibited altered shoot gravitropism, while idd3 knock-out mutants showed no visible morphological differences compared with the wild-type plants. IDD3 is ubiquitously expressed in different tissues and stages, and the IDD3 transcript was induced by exogenously applied auxin. Expression of the PIN-FORMED (PIN) and Aux/IAA genes was altered in IDD3 OX compared with wild-type plants. Furthermore, IDD3 OX plants are sensitive to auxin and the polar auxin transporter inhibitor N-1-naphthylphalamic acid (NPA). Further yeast-one hybrid, chromatin immunoprecipitation (ChIP) and transient assays revealed that IDD3 directly represses PIN1b via promoter binding. Inoculation with R. solani indicated that PIN1b RNAi plants are more susceptible to sheath blight disease (ShB) compared with the wild-type. Taken together, our analyses suggest that IDD3 controls plant architecture and the resistance of rice to ShB via the regulation of PIN auxin transporter genes.

New insight into comprehensive analysis of INDETERMINATE DOMAIN (IDD) gene family in rice

The INDETERMINATE DOMAIN (IDD) transcription factor (TF), as a family of plant-specific zinc-finger proteins, regulates a variety of development processes and abiotic stresses in plants. IDD genes have been identified and characterized in other plants, however, the rice IDD family genes have not been investigated at genome-wide. In this study, 15 OsIDD genes were identified in rice genome and phylogenetically classified into two groups. Conserved motifs and potential interaction protein analysis about OsIDD proteins were carried out. Exon-intron structures, cis-acting elements and expression profiles of OsIDD genes were also examined. Exon-intron structures analysis revealed that overall structures of OsIDD genes were relatively conserved although they contained different numbers of introns. Cis-acting elements analysis suggested that most OsIDD gene transcripts could be induced by various abiotic stresses and phytohormones. The expression patterns of OsIDD genes were detected by qRT-PCR under cold and drought conditions, and by exogenous auxin (2,4-D), gibberellin (GA₃), and abscisic acid (ABA) treatments, respectively. The results showed that the OsIDDs might play essential roles under abiotic stresses and hormone responses. Distinct expression profiles in tissues/organs suggested that OsIDDs might be involved in different development processes in rice. More interestingly, the prediction of protein-protein interactions (PPIs) revealed OsIDDs could cooperate with some histone modifiers. Yeast two-hybrid assays were performed and confirmed it. Collectively, these results provide a foundation for further elucidation on the molecular mechanisms of OsIDD genes and advance our understanding of their biological function in rice.

Step by step evolution of Indeterminate Domain (IDD) transcriptional regulators: from algae to angiosperms

INTRODUCTION

The Indeterminate Domain (IDD) proteins are a plant-specific subclass of C2H2 Zinc Finger transcription factors. Some of these transcription factors play roles in diverse aspects of plant metabolism and development, but the function of most of IDD genes is unknown and the molecular evolution of the subfamily has not been explored in detail.

METHODS

In this study, we mined available genome sequences of green plants (Viridiplantae) to reconstruct the phylogeny and then described the motifs/expression patterns of IDD genes.

KEY RESULTS

We identified the complete set of IDD genes of 16 Streptophyta genomes. We found that IDD and its sister clade STOP arose by a duplication at the base of Streptophyta. Once on land, the IDD genes duplicated extensively, giving rise to at least ten lineages. Some of these lineages were lost in extant non-vascular plants and gymnosperms, but all of them were retained in angiosperms, duplicating profoundly in dicots and monocots and acquiring, at the same time, surprising heterogeneity in their C-terminal regions and expression patterns.

CONCLUSIONS

IDDs were present in the last common ancestor of Streptophyta. On land, IDDs duplicated extensively, leading to ten lineages. Later, IDDs were recruited by angiosperms where they diversified greatly in number, C-terminal and expression patterns. Interestingly, such diversification occurred during the evolution of novel traits of the plant body. This study provides a solid framework of the orthology relationships of green land plant IDD transcription factors, thus increasing the accuracy of orthologue identification in model and non-model species and facilitating the identification of agronomically important genes related to plant metabolism and development.

Gene Regulation via the Combination of Transcription Factors in the INDETERMINATE DOMAIN and GRAS Families

INDETERMINATE DOMAIN (IDD) family proteins are plant-specific transcription factors. Some Arabidopsis IDD (AtIDD) proteins regulate the expression of SCARECROW (SCR) by interacting with GRAS family transcription factors SHORT-ROOT (SHR) and SCR, which are involved in root tissue formation. Some AtIDD proteins regulate genes involved in the synthesis (GA3ox1) or signaling (SCL3) of gibberellic acid (GA) by interacting with DELLA proteins, a subfamily of the GRAS family. We analyzed the DNA binding properties and protein–protein interactions of select AtIDD proteins. We also investigated the transcriptional activity of the combination of AtIDD and GRAS proteins (AtIDD proteins combined with SHR and SCR or with REPRESSOR of ga1-3 (RGA)) on the promoters of SCR,SCL3, and GA3ox1 by conducting a transient assay using Arabidopsis culture cells. Our results showed that the SCR promoter could be activated by the IDD and RGA complexes and that the SCL3 and GA3ox1 promoters could be activated by the IDD, SHR, and SCR complexes, indicating the possibility that these complexes regulate and consequently coordinate the expression of genes involved in GA synthesis (GA3ox1), GA signaling (SCL3), and root formation (SCR).

Coordination of light, circadian clock with temperature: The potential mechanisms regulating chilling tolerance in rice

Rice (Oryza sativa L.) is a major staple food crop for over half of the world's population. As a crop species originated from the subtropics, rice production is hampered by chilling stress. The genetic mechanisms of rice responses to chilling stress have attracted much attention, focusing on chilling-related gene mining and functional analyses. Plants have evolved sophisticated regulatory systems to respond to chilling stress in coordination with light signaling pathway and internal circadian clock. However, in rice, information about light-signaling pathways and circadian clock regulation and their roles in chilling tolerance remains elusive. Further investigation into the regulatory network of chilling tolerance in rice is needed, as knowledge of the interaction between temperature, light, and circadian clock dynamics is limited. Here, based on phenotypic analysis of transgenic and mutant rice lines, we delineate the relevant genes with important regulatory roles in chilling tolerance. In addition, we discuss the potential coordination mechanism among temperature, light, and circadian clock in regulating chilling response and tolerance of rice, and provide perspectives for the ongoing chilling signaling network research in rice.

Indeterminate Domain Proteins Regulate Rice Defense to Sheath Blight Disease

BACKGROUND

Loose Plant Architecture 1 (LPA1), an indeterminate domain (IDD) protein, exhibits almost no expression in the leaves, but the overexpression of LPA1 significantly increases the resistance of rice to sheath blight disease (ShB) via the activation of PIN-FORMED 1a (PIN1a).

RESULTS

In this study, we determined that Rhizoctonia solani infection significantly induced LPA1 expression in the leaves, and lpa1 was more susceptible to R. solani compared with the wild-type and revertant plants. In addition, infection with R. solani altered the expression of IDD3, IDD5, IDD10, and IDD13, and yeast two-hybrid, split-GFP, and coimmunoprecipitation assays showed that LPA1 interacts with IDD3 and IDD13. IDD13 RNAi plants were more susceptible, while IDD13 overexpressors were less susceptible to ShB compared with the wild-type. In parallel, idd3 exhibited no significant differences, while IDD3 overexpressors were more susceptible compared to the wild-type response to ShB. Additional chromatin-immunoprecipitation and electrophoretic mobility shift assay experiments indicated that IDD13 and IDD3 bound to the PIN1a promoter, and the transient assay indicated that IDD13 and IDD3 positively and negatively regulate PIN1a expression, respectively. Moreover, IDD13, IDD3, and LPA1 form a transcription factor complex that regulates PIN1a. A genetic study showed that the LPA1 repressor lines were similar to lpa1/IDD13 RNAi and were more susceptible than the lpa1 and IDD13 RNAi plants in response to ShB. The overexpression of IDD13 increased resistance to ShB in the lpa1 background.

CONCLUSIONS

Taken together, our analyses established that IDD3, IDD13, and LPA1 form a transcription factor complex to regulate the defense of rice against ShB possibly via the regulation of PIN1a.

Role of the INDETERMINATE DOMAIN Genes in Plants

The INDETERMINATE DOMAIN (IDD) genes comprise a conserved transcription factor family that regulates a variety of developmental and physiological processes in plants. Many recent studies have focused on the genetic characterization of IDD family members and revealed various biological functions, including modulation of sugar metabolism and floral transition, cold stress response, seed development, plant architecture, regulation of hormone signaling, and ammonium metabolism. In this review, we summarize the functions and working mechanisms of the IDD gene family in the regulatory network of metabolism and developmental processes.

UMP Kinase Regulates Chloroplast Development and Cold Response in Rice

Pyrimidine nucleotides are important metabolites that are building blocks of nucleic acids, which participate in various aspects of plant development. Only a few genes involved in pyrimidine metabolism have been identified in rice and the majority of their functions remain unclear. In this study, we used a map-based cloning strategy to isolate a UMPK gene in rice, encoding the UMP kinase that phosphorylates UMP to form UDP, from a recessive mutant with pale-green leaves. In the mutant, UDP content always decreased, while UTP content fluctuated with the development of leaves. Mutation of UMPK reduced chlorophyll contents and decreased photosynthetic capacity. In the mutant, transcription of plastid-encoded RNA polymerase-dependent genes, including psaA, psbB, psbC and petB, was significantly reduced, whereas transcription of nuclear-encoded RNA polymerase-dependent genes, including rpoA, rpoB, rpoC1, and rpl23, was elevated. The expression of UMPK was significantly induced by various stresses, including cold, heat, and drought. Increased sensitivity to cold stress was observed in the mutant, based on the survival rate and malondialdehyde content. High accumulation of hydrogen peroxide was found in the mutant, which was enhanced by cold treatment. Our results indicate that the UMP kinase gene plays important roles in regulating chloroplast development and stress response in rice.

OsIDD2, a zinc finger and INDETERMINATE DOMAIN protein, regulates secondary cell wall formation

Previously, we found 123 transcription factors (TFs) as candidate regulators of secondary cell wall (SCW) formation in rice by using phylogenetic and co-expression network analyses. Among them, we examined in this work the role of OsIDD2, a zinc finger and indeterminate domain (IDD) family TF. Its overexpressors showed dwarfism, fragile leaves, and decreased lignin content, which are typical phenotypes of plants defective in SCW formation, whereas its knockout plants showed slightly increased lignin content. The RNA-seq and quantitative reverse transcription polymerase chain reaction analyses confirmed that some lignin biosynthetic genes were downregulated in the OsIDD2-overexpressing plants, and revealed the same case for other genes involved in cellulose synthesis and sucrose metabolism. The transient expression assay using rice protoplasts revealed that OsIDD2 negatively regulates the transcription of genes involved in lignin biosynthesis, cinnamyl alcohol dehydrogenase 2 and 3 (CAD2 and 3), and sucrose metabolism, sucrose synthase 5 (SUS5), whereas an AlphaScreen assay, which can detect the interaction between TFs and their target DNA sequences, directly confirmed the interaction between OsIDD2 and the target sequences located in the promoter regions of CAD2 and CAD3. Based on these observations, we conclude that OsIDD2 is negatively involved in SCW formation and other biological events by downregulating its target genes.

Gene Regulation and Signal Transduction in the ICE-CBF-COR Signaling Pathway during Cold Stress in Plants

Low temperature is an abiotic stress that adversely affects the growth and production of plants. Resistance and adaptation of plants to cold stress is dependent upon the activation of molecular networks and pathways involved in signal transduction and the regulation of cold-stress related genes. Because it has numerous and complex genes, regulation factors, and pathways, research on the ICE-CBF-COR signaling pathway is the most studied and detailed, which is thought to be rather important for cold resistance of plants. In this review, we focus on the function of each member, interrelation among members, and the influence of manipulators and repressors in the ICE-CBF-COR pathway. In addition, regulation and signal transduction concerning plant hormones, circadian clock, and light are discussed. The studies presented provide a detailed picture of the ICE-CBF-COR pathway.

Overexpressing IbCBF3 increases low temperature and drought stress tolerance in transgenic sweetpotato

Dehydration-responsive element-binding/C-repeat-binding factor (DREB/CBF) proteins regulate the transcription of genes involved in cold acclimation in several species. However, little is known about the physiological functions of CBF proteins in the low temperature-sensitive crop sweetpotato. We previously reported that the DREB1/CBF-like sweetpotato gene SwDREB1/IbCBF3 is involved in responses to diverse abiotic stresses. In this study, we confirmed that IbCBF3 is localized to the nucleus and binds to the C-repeat/dehydration-responsive elements (CRT/DRE) in the promoters of cold-regulated (COR) genes. We generated transgenic sweetpotato plants overexpressing IbCBF3 under the control of the CaMV 35S promoter (referred to as SC plants) and evaluated their responses to various abiotic stresses. IbCBF3 expression was dramatically induced by cold and drought but much less strongly induced by high salinity and ABA. We further characterized two SC lines (SC3 and SC6) with high levels of IbCBF3 transcript. The SC plants displayed enhanced tolerance to cold, drought, and oxidative stress on the whole-plant level. Under cold stress treatment (4 °C for 48 h), severe wilting and chilling injury were observed in the leaves of wild-type (WT) plants, whereas SC plants were not affected by cold stress. In addition, the COR genes were significantly upregulated in SC plants compared with the WT. The SC plants also showed significantly higher tolerance to drought stress than the WT, which was associated with higher photosynthesis efficiency and lower hydrogen peroxide levels. These results indicate that IbCBF3 is a functional transcription factor involved in the responses to various abiotic stresses in sweetpotato.