The NAC transcription factor ONAC083 negatively regulates rice immunity against Magnaporthe oryzae by directly activating transcription of the RING-H2 gene OsRFPH2-6

Plant NAC transcription factors in the battle against pathogens

BACKGROUND

The NAC transcription factor family, which is recognized as one of the largest plant-specific transcription factor families, comprises numerous members that are widely distributed among various higher plant species and play crucial regulatory roles in plant immunity.

RESULTS

In this paper, we provided a detailed summary of the roles that NAC transcription factors play in plant immunity via plant hormone pathways and reactive oxygen species pathways. In addition, we conducted in-depth investigations into the interactions between NAC transcription factors and pathogen effectors to summarize the mechanism through which they regulate the expression of defense-related genes and ultimately affect plant disease resistance.

CONCLUSIONS

This paper presented a comprehensive overview of the crucial roles that NAC transcription factors play in regulating plant disease resistance through their involvement in diverse signaling pathways, acting as either positive or negative regulators, and thus provided references for further research on NAC transcription factors.

OsWRKY70 Plays Opposite Roles in Blast Resistance and Cold Stress Tolerance in Rice

The transcription factor WRKYs play pivotal roles in the adapting to adverse environments in plants. Prior research has demonstrated the involvement of OsWRKY70 in resistance against herbivores and its response to abiotic stress. Here, we reported the functional analysis of OsWRKY70 in immunity against fungal diseases and cold tolerance. The results revealed that OsWRKY70 was induced by various Magnaporthe oryzae strains. Knock out mutants of OsWRKY70, which were generated by the CRISPR/Cas9 system, exhibited enhanced resistance to M. oryzae. This was consistent with fortifying the reactive oxygen species (ROS) burst after inoculation in the mutants, elevated transcript levels of defense-responsive genes (OsPR1b, OsPBZ1, OsPOX8.1 and OsPOX22.3) and the observation of the sluggish growth of invasive hyphae under fluorescence microscope. RNA sequencing (RNA-seq) and quantitative real-time PCR (qRT-PCR) validations demonstrated that differentially expressed genes were related to plant-pathogen interactions, hormone transduction and MAPK cascades. Notably, OsbHLH6, a key component of the JA signaling pathway, was down-regulated in the mutants compared to wild type plants. Further investigation confirmed that OsWRKY70 bound to the promoter of OsbHLH6 by semi-in vivo chromatin immunoprecipitation (ChIP). Additionally, the loss-function of OsWRKY70 impaired cold tolerance in rice. The enhanced susceptibility in the mutants characterized by excessive ROS production, elevated ion leakage rate and increased malondialdehyde content, as well as decreased activity of catalase (CAT) and peroxidase (POD) under low temperature stress was, which might be attributed to down-regulation of cold-responsive genes (OsLti6b and OsICE1). In conclusion, our findings indicate that OsWRKY70 negatively contributes to blast resistance but positively regulates cold tolerance in rice, providing a strategy for crop breeding with tolerance to stress.

Rice E3 ubiquitin ligases: From key modulators of host immunity to potential breeding applications

To combat pathogen attacks, plants have developed a highly advanced immune system, which requires tight regulation to initiate robust defense responses while simultaneously preventing autoimmunity. The ubiquitin-proteasome system (UPS), which is responsible for degrading excess or misfolded proteins, has vital roles in ensuring strong and effective immune responses. E3 ligases, as key UPS components, play extensively documented roles in rice immunity by modulating the ubiquitination and degradation of downstream substrates involved in various immune signaling pathways. Here, we summarize the crucial roles of rice E3 ligases in both pathogen/microbe/damage-associated molecular pattern-triggered immunity and effector-triggered immunity, highlight the molecular mechanisms by which E3 ligases function in rice immune signaling, and emphasize the functions of E3 ligases as targets of pathogen effectors for pathogenesis. We also discuss potential strategies for application of immunity-associated E3 ligases in breeding of disease-resistant rice varieties without growth penalty. This review provides a comprehensive and updated understanding of the sophisticated and interconnected regulatory functions of E3 ligases in rice immunity and in balancing immunity with growth and development.

A distinct protein posttranslational modifications-linked OsATL32-OsPPKL2-OsGSK2 loop modulates rice immunity against blast disease

Protein posttranslational modifications play crucial roles in plant immunity through modulating a complicated signaling network mediated by different hormones. We previously demonstrated that OsATL32, an ATL-type E3 ligase, negatively contributes to rice immunity against Magnaporthe oryzae. Here, we show that OsATL32 forms a loop with OsPPKL2 and OsGSK2 through distinct protein posttranslational modifications to modulate rice immunity. OsATL32 ubiquitinates OsPPKL2, a protein phosphatase with Kelch-like repeat domains that exerts positive roles in regulating rice immunity against M. oryzae and chitin-triggered immune responses, for degradation. The glycogen synthase kinase 2 (OsGSK2), which acts as a negative regulator of rice immunity against M. oryzae and chitin-triggered immune responses, phosphorylates OsATL32 to elevate its protein stability and E3 ligase activity on OsPPKL2. Moreover, OsPPKL2 directly dephosphorylates OsGSK2, affecting its kinase activity on substrates including OsATL32 for phosphorylation. Like OsGSK2 as a BR signaling repressor, OsATL32 negatively regulates BR signaling; conversely, OsPPKL2 plays a positive role in BR signaling. These findings provide a molecular mechanism in which OsATL32 serves as a node connecting BR signaling and immunity by associating with OsPPKL2 and OsGSK2, assembling into a distinct protein posttranslational modifications-linked loop that functions in rice BR signaling and immunity.

A NAC transcription factor MNAC3-centered regulatory network negatively modulates rice immunity against blast disease

NAC transcription factors (TFs) are pivotal in plant immunity against diverse pathogens. Here, we report the functional and regulatory network of MNAC3, a novel NAC TF, in rice immunity. MNAC3, a transcriptional activator, negatively modulates rice immunity against blast and bacterial leaf blight diseases and pathogen-associated molecular pattern (PAMP)-triggered immune responses. MNAC3 binds to a CACG cis-element and activates the transcription of immune-negative target genes OsINO80, OsJAZ10, and OsJAZ11. The negative function of MNAC3 in rice immunity depends on its transcription of downstream genes such as OsINO80 and OsJAZ10. MNAC3 interacts with immunity-related OsPP2C41 (a protein phosphatase), ONAC066 (a NAC TF), and OsDjA6 (a DnaJ chaperone). ONAC066 and OsPP2C41 attenuate MNAC3 transcriptional activity, while OsDjA6 promotes it. Phosphorylation of MNAC3 at S163 is critical for its negative functions in rice immunity. OsPP2C41, which plays positive roles in rice blast resistance and chitin-triggered immune responses, dephosphorylates MNAC3, suppressing its transcriptional activity on the target genes OsINO80, OsJAZ10, and OsJAZ11 and promoting the translocation of MNAC3 from nucleus to cytoplasm. These results establish a MNAC3-centered regulatory network in which OsPP2C41 dephosphorylates MNAC3, attenuating its transcriptional activity on downstream immune-negative target genes in rice. Together, these findings deepen our understanding of molecular mechanisms in rice immunity and offer a novel strategy for genetic improvement of rice disease resistance.

OsATL32 ubiquitinates the reactive oxygen species-producing OsRac5-OsRbohB module to suppress rice immunity

Ubiquitination-mediated protein degradation is integral to plant immunity, with E3 ubiquitin ligases acting as key factors in this process. Here, we report the functions of OsATL32, a plasma membrane-localized Arabidopsis Tóxicos En Levadura (ATL)-type E3 ubiquitin ligase, in rice (Oryza sativa) immunity and its associated regulatory network. We found that the expression of OsATL32 is downregulated in both compatible and incompatible interactions between rice and the rice blast fungus Magnaporthe oryzae. The OsATL32 protein level declines in response to infection by a compatible M. oryzae strain or to chitin treatment. OsATL32 negatively regulates rice resistance to blast and bacterial leaf blight diseases, as well as chitin-triggered immunity. Biochemical and genetic studies revealed that OsATL32 suppresses pathogen-induced reactive oxygen species (ROS) accumulation by mediating ubiquitination and degradation of the ROS-producing OsRac5-OsRbohB module, which enhances rice immunity against M. oryzae. The protein phosphatase PHOSPHATASE AND TENSIN HOMOLOG enhances rice blast resistance by dephosphorylating OsATL32 and promoting its degradation, preventing its negative effect on rice immunity. This study provides insights into the molecular mechanism by which the E3 ligase OsATL32 targets a ROS-producing module to undermine rice immunity.

The MYB transcription factor OsMYBxoc1 regulates resistance to Xoc by directly repressing transcription of the iron transport gene OsNRAMP5 in rice

Bacterial leaf streak caused by Xanthomonas oryzae pv. oryzicola (Xoc) is a continuous threat to rice cultivation, leading to substantial yield losses with socioeconomic implications. Iron ions are essential mineral nutrients for plant growth, but little information is available on how they influence mechanisms of rice immunity against Xoc. Here, we investigated the role of the myeloblastosis-related (MYB) transcriptional repressor OsMYBxoc1 in modulation of rice resistance through control of iron ion transport. Overexpression of OsMYBxoc1 significantly increased rice resistance, whereas OsMYBxoc1 RNA-interference lines and knockout mutants showed the opposite result. Suppression of OsMYBxoc1 expression dampened the immune response induced by pathogen-associated molecular patterns. We demonstrated that OsMYBxoc1 binds specifically to the OsNRAMP5 promoter and represses transcription of OsNRAMP5. OsNRAMP5, a negative regulator of rice resistance to bacterial leaf streak, possesses metal ion transport activity, and inhibition of OsMYBxoc1 expression increased the iron ion content in rice. Activity of the ion-dependent H2O2 scavenging enzyme catalase was increased in plants with suppressed expression of OsMYBxoc1 or overexpression of OsNRAMP5. We found that iron ions promoted Xoc infection and interfered with the production of reactive oxygen species induced by Xoc. The type III effector XopAK directly inhibited OsMYBxoc1 transcription, indicating that the pathogen may promote its own proliferation by relieving restriction of iron ion transport in plants. In addition, iron complemented the pathogenicity defects of the RS105_ΔXopAK mutant strain, further confirming that iron utilization by Xoc may be dependent upon XopAK. In conclusion, our study reveals a novel mechanism by which OsMYBxoc1 modulates rice resistance by regulating iron accumulation and demonstrates that Xoc can accumulate iron ions by secreting the effector XopAK to promote its own infection.

Characteristics of NAC transcription factors in Solanaceae crops and their roles in responding to abiotic and biotic stresses

As one of the largest transcription factor (TF) families in plants, the NAC (NAM, ATAF1/2, and CUC2) family plays important roles in response pathways to various abiotic and biotic stresses, such as drought, high salinity, low temperature, and pathogen infection. Although, there are a number of reviews on the involvement of NAC TF in plant responses to biotic and abiotic stresses, most of them are focused on the model plants Arabidopsis thaliana and Oryza sativa, and there is a lack of systematic evaluation of specific species. Solanaceae, the world's third most significant cash crop, has been seriously affected by environmental disturbances in recent years in terms of yield and quality, posing a severe threat to global food security. This review focuses on the functional roles of NAC transcription factors in response to external stresses involved in five important Solanaceae crops: tomato, potato, pepper, eggplant and tobacco, and analyzes the affinities between them. It will provide resources for stress-resistant breeding of Solanaceae crops using transgenic technology.

Overexpression of a Fragaria vesca NAM, ATAF, and CUC (NAC) Transcription Factor Gene (FvNAC29) Increases Salt and Cold Tolerance in Arabidopsis thaliana

The NAC (NAM, ATAF1/2, CUC2) family of transcription factors (TFs) is a vital transcription factor family of plants. It controls multiple parts of plant development, tissue formation, and abiotic stress response. We cloned the FvNAC29 gene from Fragaria vesca (a diploid strawberry) for this research. There is a conserved NAM structural domain in the FvNAC29 protein. The highest homology between FvNAC29 and PaNAC1 was found by phylogenetic tree analysis. Subcellular localization revealed that FvNAC29 is localized onto the nucleus. Compared to other tissues, the expression level of FvNAC29 was higher in young leaves and roots. In addition, Arabidopsis plants overexpressing FvNAC29 had higher cold and high-salinity tolerance than the wild type (WT) and unloaded line with empty vector (UL). The proline and chlorophyll contents of transgenic Arabidopsis plants, along with the activities of the antioxidant enzymes like catalase (CAT), peroxidase (POD), and superoxide dismutase (SOD) under 200 mM NaCl treatment or -8 °C treatment, were higher than those activities of the control. Meanwhile, malondialdehyde (MDA) and the reactive oxygen species (ROS) content were higher in the WT and UL lines. FvNAC29 improves transgenic plant resistance to cold and salt stress by regulating the expression levels of AtRD29a, AtCCA1, AtP5CS1, and AtSnRK2.4. It also improves the potential to tolerate cold stress by positively regulating the expression levels of AtCBF1, AtCBF4, AtCOR15a, and AtCOR47. These findings suggest that FvNAC29 may be related to the processes and the molecular mechanisms of F. vesca response to high-salinity stress and LT stress, providing a comprehensive understanding of the NAC TFs.

Mno-miR164a and MnNAC100 regulate the resistance of mulberry to Botrytis cinerea

Although microRNAs (miRNAs) regulate the defense response of a variety of plant species against a variety of pathogenic fungi, the involvement of miRNAs in mulberry's defense against Botrytis cinerea has not yet been documented. In this study, we identified responsive B. cinerea miRNA mno-miR164a in mulberry trees. After infection with B. cinerea, the expression of mno-miR164a was reduced, which was fully correlated with the upregulation of its target gene, MnNAC100, responsible for encoding a transcription factor. By using transient infiltration/VIGS mulberry that overexpressed mno-miR164a or knocked-down MnNAC100, our study revealed a substantial enhancement in mulberry's resistance to B. cinerea when mno-miR164a was overexpressed or MnNAC100 expression was suppressed. This enhancement was accompanied by increased catalase (CAT) activity and reduced malondialdehyde (MDA) content. In addition, mno-miR164a-mediated inhibition of MnNAC100 enhanced the expression of a cluster of defense-related genes in transgenic plants upon exposure to B. cinerea. Meanwhile, MnNAC100 acts as a transcriptional repressor, directly suppressing the expression of MnPDF1.2. Our study indicated that the mno-miR164a-MnNAC100 regulatory module manipulates the defense response of mulberry to B. cinerea infection. This discovery has great potential in breeding of resistant varieties and disease control.

IbNIEL-mediated degradation of IbNAC087 regulates jasmonic acid-dependent salt and drought tolerance in sweet potato

Sweet potato (Ipomoea batatas [L.] Lam.) is a crucial staple and bioenergy crop. Its abiotic stress tolerance holds significant importance in fully utilizing marginal lands. Transcriptional processes regulate abiotic stress responses, yet the molecular regulatory mechanisms in sweet potato remain unclear. In this study, a NAC (NAM, ATAF1/2, and CUC2) transcription factor, IbNAC087, was identified, which is commonly upregulated in salt- and drought-tolerant germplasms. Overexpression of IbNAC087 increased salt and drought tolerance by increasing jasmonic acid (JA) accumulation and activating reactive oxygen species (ROS) scavenging, whereas silencing this gene resulted in opposite phenotypes. JA-rich IbNAC087-OE (overexpression) plants exhibited more stomatal closure than wild-type (WT) and IbNAC087-Ri plants under NaCl, polyethylene glycol, and methyl jasmonate treatments. IbNAC087 functions as a nuclear transcriptional activator and directly activates the expression of the key JA biosynthesis-related genes lipoxygenase (IbLOX) and allene oxide synthase (IbAOS). Moreover, IbNAC087 physically interacted with a RING-type E3 ubiquitin ligase NAC087-INTERACTING E3 LIGASE (IbNIEL), negatively regulating salt and drought tolerance in sweet potato. IbNIEL ubiquitinated IbNAC087 to promote 26S proteasome degradation, which weakened its activation on IbLOX and IbAOS. The findings provide insights into the mechanism underlying the IbNIEL-IbNAC087 module regulation of JA-dependent salt and drought response in sweet potato and provide candidate genes for improving abiotic stress tolerance in crops.

Cooperative transcriptional regulation by ATAF1 and HY5 promotes light-induced cotyledon opening in Arabidopsis thaliana

The opening of the embryonic leaves (cotyledons) as seedlings emerge from the dark soil into the light is crucial to ensure the survival of the plant. Seedlings that sprout in the dark elongate rapidly to reach light but keep their cotyledons closed. During de-etiolation, the transition from dark to light growth, elongation slows and the cotyledons open. Here, we report that the transcription factor ACTIVATING FACTOR1 (ATAF1) participates in de-etiolation and facilitates light-induced cotyledon opening. The transition from dark to light rapidly induced ATAF1 expression and ATAF1 accumulation in cotyledons. Seedlings lacking or overexpressing ATAF1 exhibited reduced or enhanced cotyledon opening, respectively, and transcriptomic analysis indicated that ATAF1 repressed the expression of genes associated with growth and cotyledon closure. The activation of the photoreceptor phytochrome A (phyA) by far-red light induced its association with the ATAF1 promoter and stimulation of ATAF1 expression. The transcription factor ELONGATED HYPOCOTYL5 (HY5), which is also activated in response far-red light, cooperated with phyA to induce ATAF1 expression. ATAF1 and HY5 interacted with one another and cooperatively repressed the expression of growth-promoting and cotyledon closure genes. Together, our study reveals a mechanism through which far-red light promotes cotyledon opening.

Causal role of a promoter polymorphism in natural variation of the Arabidopsis floral repressor gene FLC

Noncoding polymorphism frequently associates with phenotypic variation, but causation and mechanism are rarely established. Noncoding single-nucleotide polymorphisms (SNPs) characterize the major haplotypes of the Arabidopsis thaliana floral repressor gene FLOWERING LOCUS C (FLC). This noncoding polymorphism generates a range of FLC expression levels, determining the requirement for and the response to winter cold. The major adaptive determinant of these FLC haplotypes was shown to be the autumnal levels of FLC expression. Here, we investigate how noncoding SNPs influence FLC transcriptional output. We identify an upstream transcription start site (uTSS) cluster at FLC, whose usage is increased by an A variant at the promoter SNP-230. This variant is present in relatively few Arabidopsis accessions, with the majority containing G at this site. We demonstrate a causal role for the A variant at -230 in reduced FLC transcriptional output. The G variant upregulates FLC expression redundantly with the major transcriptional activator FRIGIDA (FRI). We demonstrate an additive interaction of SNP-230 with an intronic SNP+259, which also differentially influences uTSS usage. Combinatorial interactions between noncoding SNPs and transcriptional activators thus generate quantitative variation in FLC transcription that has facilitated the adaptation of Arabidopsis accessions to distinct climates.

Mapping QTL conferring flag leaf senescence in durum wheat cultivars

Flag leaf senescence is a critical factor affecting the yield and quality of wheat. The aim of this study was to identify QTLs associated with flag leaf senescence in an F10 recombinant inbred line population derived from durum wheats UC1113 and Kofa. Bulked segregant analysis using the wheat 660K SNP array identified 3225 SNPs between extreme-phenotype bulks, and the differential SNPs were mainly clustered on chromosomes 1A, 1B, 3B, 5A, 5B, and 7A. BSR-Seq indicated that the significant SNPs were mainly located in two intervals of 354.0-389.0 Mb and 8.0-15.0 Mb on 1B and 3B, respectively. Based on the distribution of significant SNPs on chromosomes 1B and 3B, a total of 109 insertion/deletion (InDel) markers were developed, and 8 of them were finally used to map QTL in UC1113/Kofa population for flag leaf senescence. Inclusive composite interval mapping identified two major QTL in marker intervals Mar2005-Mar2116 and Mar207-Mar289, explaining 14.2-15.4% and 31.4-68.6% of the phenotypic variances across environments, respectively. Using BSR-Seq, gene expression and sequence analysis, the TraesCS1B02G211600 and TraesCS3B02G023000 were identified as candidate senescence-associated genes. This study has potential to be used in cloning key genes for flag leaf senescence and provides available molecular markers for genotyping and marker-assisted selection breeding.

Supplementary Information

The online version contains supplementary material available at 10.1007/s11032-023-01410-3.