Arabidopsis exoribonuclease USB1 interacts with the PPR-domain protein SOAR1 to negatively regulate abscisic acid signaling

Integrating the multiple functions of CHLH into chloroplast-derived signaling fundamental to plant development and adaptation as well as fruit ripening

Chlorophyll (Chl)-mediated oxygenic photosynthesis sustains life on Earth. Greening leaves play fundamental roles in plant growth and crop yield, correlating with the idea that more Chls lead to better adaptation. However, they face significant challenges from various unfavorable environments. Chl biosynthesis hinges on the first committed step, which involves inserting Mg2+ into protoporphyrin. This step is facilitated by the H subunit of magnesium chelatase (CHLH) and features a conserved mechanism from cyanobacteria to plants. For better adaptation to fluctuating land environments, especially drought, CHLH evolves multiple biological functions, including Chl biosynthesis, retrograde signaling, and abscisic acid (ABA) responses. Additionally, it integrates into various chloroplast-derived signaling pathways, encompassing both retrograde signaling and hormonal signaling. The former comprises ROS (reactive oxygen species), heme, GUN (genomes uncoupled), MEcPP (methylerythritol cyclodiphosphate), β-CC (β-cyclocitral), and PAP (3'-phosphoadenosine-5'-phosphate). The latter involves phytohormones like ABA, ethylene, auxin, cytokinin, gibberellin, strigolactone, brassinolide, salicylic acid, and jasmonic acid. Together, these elements create a coordinated regulatory network tailored to plant development and adaptation. An intriguing example is how drought-mediated improvement of fruit quality provides insights into chloroplast-derived signaling, aiding the shift from vegetative to reproductive growth. In this context, we explore the integration of CHLH's multifaceted roles into chloroplast-derived signaling, which lays the foundation for plant development and adaptation, as well as fruit ripening and quality. In the future, manipulating chloroplast-derived signaling may offer a promising avenue to enhance crop yield and quality through the homeostasis, function, and regulation of Chls.

Talaromyces marneffei suppresses macrophage inflammation by regulating host alternative splicing

Talaromyces marneffei (T. marneffei) immune escape is essential in the pathogenesis of talaromycosis. It is currently known that T. marneffei achieves immune escape through various strategies. However, the role of cellular alternative splicing (AS) in immune escape remains unclear. Here, we depict the AS landscape in macrophages upon T. marneffei infection via high-throughput RNA sequencing and detect a truncated protein of NCOR2 / SMRT, named NCOR2-013, which is significantly upregulated after T. marneffei infection. Mechanistic analysis indicates that NCOR2-013 forms a co-repression complex with TBL1XR1 / TBLR1 and HDAC3, thereby inhibiting JunB-mediated transcriptional activation of pro-inflammatory cytokines via the inhibition of histone acetylation. Furthermore, we identify TUT1 as the AS regulator that regulates NCOR2-013 production and promotes T. marneffei immune evasion. Collectively, these findings indicate that T. marneffei escapes macrophage killing through TUT1-mediated alternative splicing of NCOR2 / SMRT, providing insight into the molecular mechanisms of T. marneffei immune evasion and potential targets for talaromycosis therapy.

A Genome-Wide Analysis of the Pentatricopeptide Repeat Protein Gene Family in Two Kiwifruit Species with an Emphasis on the Role of RNA Editing in Pathogen Stress

Kiwifruit is a perennial fruit tree with high nutritional and economic value; however, various pathogen stresses have resulted in reductions in its yield and quality. Pentatricopeptide repeat proteins (PPRs), characterized by tandem repetitions of 35 amino acid motifs, play roles in RNA editing, mRNA stability, and splicing. They may also regulate plant development and growth. Nevertheless, the roles of PPRs in plant development and disease resistance remain unclear. In this study, we focused on the roles of PPRs in the fruit development and pathogen stress of kiwifruit and conducted a series of analyses of the PPR gene family in two representative kiwifruit species (Actinidia chinensis (Ach) and Actinidia eriantha (Ace)) with markedly different degrees of disease resistance. A total of 497 and 499 PPRs were identified in Ach and Ace, respectively. All the kiwifruit PPRs could be phylogenetically divided into four subfamilies. There were about 40.68% PPRs predicted to be localized to mitochondria or chloroplasts. A synteny analysis showed that the expansion of the kiwifruit PPRs mainly originated from segmental duplication. Based on RNA-seq data from the fruit over 12 periods of development and maturity, a weighted correlation network analysis suggested that two PPRs, Actinidia20495.t1 and Actinidia15159.t1, may be involved in fruit development and maturation. In addition, we observed different responses with respect to the expression of PPRs and RNA editing between resistant and susceptible kiwifruits following infection with pathogenic bacteria, indicating the regulatory role of PPRs in the stress response via the modulation of RNA editing. The differentially expressed upstream transcription factors of the PPRs were further identified; they may regulate resistance adaption by modulating the expression of the PPRs. Collectively, these results suggest that PPRs play roles in the development and disease resistance of kiwifruit and provide candidate genes for further clarifying the resistance mechanisms in kiwifruits.

Identification of novel candidate loci and genes for seed vigor-related traits in upland cotton (Gossypium hirsutum L.) via GWAS

Seed vigor (SV) is a crucial trait determining the quality of crop seeds. Currently, over 80% of China's cotton-planting area is in Xinjiang Province, where a fully mechanized planting model is adopted, accounting for more than 90% of the total fiber production. Therefore, identifying SV-related loci and genes is crucial for improving cotton yield in Xinjiang. In this study, three seed vigor-related traits, including germination potential, germination rate, and germination index, were investigated across three environments in a panel of 355 diverse accessions based on 2,261,854 high-quality single-nucleotide polymorphisms (SNPs). A total of 26 significant SNPs were detected and divided into six quantitative trait locus regions, including 121 predicted candidate genes. By combining gene expression, gene annotation, and haplotype analysis, two novel candidate genes (Ghir_A09G002730 and Ghir_D03G009280) within qGR-A09-1 and qGI/GP/GR-D03-3 were associated with vigor-related traits, and Ghir_A09G002730 was found to be involved in artificial selection during cotton breeding by population genetic analysis. Thus, understanding the genetic mechanisms underlying seed vigor-related traits in cotton could help increase the efficiency of direct seeding by molecular marker-assisted selection breeding.

Two environmental signal-driven RNA metabolic processes: Alternative splicing and translation

Plants live in fixed locations and have evolved adaptation mechanisms that integrate multiple responses to various environmental signals. Among the different components of these response pathways, receptors/sensors represent nodes that recognise environmental signals. Additionally, RNA metabolism plays an essential role in the regulation of gene expression and protein synthesis. With the development of RNA biotechnology, recent advances have been made in determining the roles of RNA metabolism in response to different environmental signals-especially the roles of alternative splicing and translation. In this review, we discuss recent progress in research on how the environmental adaptation mechanisms in plants are affected at the posttranscriptional level. These findings improve our understanding of the mechanism through which plants adapt to environmental changes by regulating the posttranscriptional level and are conducive for breeding stress-tolerant plants to cope with dynamic and rapidly changing environments.

The PPR-Domain Protein SOAR1 Regulates Salt Tolerance in Rice

Previous studies in Arabidopsis reported that the PPR protein SOAR1 plays critical roles in plant response to salt stress. In this study, we reported that expression of the Arabidopsis SOAR1 (AtSOAR1) in rice significantly enhanced salt tolerance at seedling growth stage and promoted grain productivity under salt stress without affecting plant productivity under non-stressful conditions. The transgenic rice lines expressing AtSOAR1 exhibited increased ABA sensitivity in ABA-induced inhibition of seedling growth, and showed altered transcription and splicing of numerous genes associated with salt stress, which may explain salt tolerance of the transgenic plants. Further, we overexpressed the homologous gene of SOAR1 in rice, OsSOAR1, and showed that transgenic plants overexpressing OsSOAR1 enhanced salt tolerance at seedling growth stage. Five salt- and other abiotic stress-induced SOAR1-like PPRs were also identified. These data showed that the SOAR1-like PPR proteins are positively involved in plant response to salt stress and may be used for crop improvement in rice under salinity conditions through transgenic manipulation.

The key clock component ZEITLUPE (ZTL) negatively regulates ABA signaling by degradation of CHLH in Arabidopsis

Ubiquitination-mediated protein degradation plays important roles in ABA signal transduction and delivering responses to chloroplast stress signals in plants, but additional E3 ligases of protein ubiquitination remain to be identified to understand the complex signaling network. Here we reported that ZEITLUPE (ZTL), an F-box protein, negatively regulates abscisic acid (ABA) signaling during ABA-inhibited early seedling growth and ABA-induced stomatal closure in Arabidopsis thaliana. Using molecular biology and biochemistry approaches, we demonstrated that ZTL interacts with and ubiquitinates its substrate, CHLH/ABAR (Mg-chelatase H subunit/putative ABA receptor), to modulate CHLH stability via the 26S proteasome pathway. CHLH acts genetically downstream of ZTL in ABA and drought stress signaling. Interestingly, ABA conversely induces ZTL phosphorylation, and high levels of ABA also induce CHLH proteasomal degradation, implying that phosphorylated ZTL protein may enhance the affinity to CHLH, leading to the increased degradation of CHLH after ABA treatment. Taken together, our results revealed a possible mechanism of reciprocal regulation between ABA signaling and the circadian clock, which is thought to be essential for plant fitness and survival.

Exogenous melatonin increases salt tolerance in bitter melon by regulating ionic balance, antioxidant system and secondary metabolism-related genes

BACKGROUND

Melatonin is a multi-functional molecule widely employed in order to mitigate abiotic stress factors, in general and salt stress in particular. Even though previous reports revealed that melatonin could exhibit roles in promoting seed germination and protecting plants during various developmental stages of several plant species under salt stress, no reports are available with respect to the regulatory acts of melatonin on the physiological and biochemical status as well as the expression levels of defense- and secondary metabolism-related related transcripts in bitter melon subjected to the salt stress.

RESULTS

Herewith the present study, we performed a comprehensive analysis of the physiological and ion balance, antioxidant system, as well as transcript analysis of defense-related genes (WRKY1, SOS1, PM H⁺-ATPase, SKOR, Mc5PTase7, and SOAR1) and secondary metabolism-related gene expression (MAP30, α-MMC, polypeptide-P, and PAL) in salt-stressed bitter melon (Momordica charantia L.) plants in response to melatonin treatment. In this regard, different levels of melatonin (0, 75 and 150 µM) were applied to mitigate salinity stress (0, 50 and 100 mM NaCl) in bitter melon. Accordingly, present findings revealed that 100 mM salinity stress decreased growth and photosynthesis parameters (SPAD, ^Fv/_Fo, Y(II)), RWC, and some nutrient elements (K⁺, Ca²⁺, and P), while it increased Y(NO), Y(NPQ), proline, Na⁺, Cl^-, H₂O₂, MDA, antioxidant enzyme activity, and lead to the induction of the examined genes. However, prsiming with 150 µM melatonin increased SPAD, ^Fv/_Fo, Y(II)), RWC, and K⁺, Ca²⁺, and P concentration while decreased Y(NO), Y(NPQ), Na⁺, Cl^-, H₂O₂, and MDA under salt stress. In addition, the antioxidant system and gene expression levels were increased by melatonin (150 µM).

CONCLUSIONS

Overall, it can be postulated that the application of melatonin (150 µM) has effective roles in alleviating the adverse impacts of salinity through critical modifications in plant metabolism.

Plant hormone regulation of abiotic stress responses

Plant hormones are signalling compounds that regulate crucial aspects of growth, development and environmental stress responses. Abiotic stresses, such as drought, salinity, heat, cold and flooding, have profound effects on plant growth and survival. Adaptation and tolerance to such stresses require sophisticated sensing, signalling and stress response mechanisms. In this Review, we discuss recent advances in understanding how diverse plant hormones control abiotic stress responses in plants and highlight points of hormonal crosstalk during abiotic stress signalling. Control mechanisms and stress responses mediated by plant hormones including abscisic acid, auxin, brassinosteroids, cytokinins, ethylene and gibberellins are discussed. We discuss new insights into osmotic stress sensing and signalling mechanisms, hormonal control of gene regulation and plant development during stress, hormone-regulated submergence tolerance and stomatal movements. We further explore how innovative imaging approaches are providing insights into single-cell and tissue hormone dynamics. Understanding stress tolerance mechanisms opens new opportunities for agricultural applications.