Journal of Experimental Botany最新文献

GIGANTEA is a multifaceted plant-specific protein that originated in a streptophyte ancestor. The current known functions of GI include circadian clock control, light signalling, flowering time regulation, stomata response, chloroplast biogenesis, accumulation of anthocyanin, chlorophyll, and starch, phytohormone signalling, senescence and response to drought, salt, and oxidative stress. Six decades since its discovery, no functional domains have been defined, and its mechanism of action is still not well-characterised. In this review, we explore the functional evolution of GI to distinguish between ancestral and more recently acquired roles. GI integrated itself into various existing signalling pathways of the circadian clock, blue light, photoperiod, and osmotic and oxidative stress response. It also evolved parallelly to acquire new functions for chloroplast accumulation, red light signalling and anthocyanin production. In this review, we have encapsulated the known mechanisms of various biological functions of GI. Additionally, this manuscript will throw light on the evolution of GI in plant lineage.

The inducer β-aminobutyric acid (BABA) is capable of immune response in various plants. However, the specific mitogen-activated protein kinase (MAPK) cascade involved in BABA-induced resistance (BABA-IR) has not yet been elucidated. Here, peach fruits treated with the BABA exhibited a pattern-triggered immunity (PTI) defense against Rhizopus stolonifer, accompanied by the generation of reactive oxygen species (ROS) and activation of MAPK cascade. Transcriptome sequencing suggested a total of fifteen PpMAPKKK/PpMAPKK/PpMAPK genes involved in BABA-IR in peach fruit. Further qRT-PCR analysis showed that the transcript profiles of PpMAPKKK3, PpMAPKK5 and PpMAPK1 were obviously potentiated. Subsequently, yeast two-hybrid (Y2H), luciferase complementation imaging (LCI), pull-down and in vitro phosphorylation assays were conducted to characterize the complete MAPK cascade (PpMAPKKK3-PpMAPKK5-PpMAPK1) involved in peach fruit. Moreover, the downstream events of MAPK1 include the involvement of SNARE13 and the corresponding NPR1-responsive defense. Single silencing of MAPKKK3, MAPKK5 or MAPK1 and double silencing of MAPKKK3/MAPKK5 or MAPKK5/MAPK1 resulted in enhanced susceptibility to the fungus R. stolonifer in mutants and attenuated salicylic acid (SA)-dependent defense gene expression; in contrast, the homologous or heterologous overexpression of PpSNARE13 in peach fruit or Arabidopsis led to an enhanced SA pool and elevated expression of PR genes. Reciprocally, the ppsnare13cas9 mutants are generally compromised in the priming of SA-dependent resistance. Therefore, the MAPKKK3-MAPKK5-MAPK1 cascade contributes to PTI signal transduction in BABA-elicited peach fruit, by combination with downstream events such as SNARE13, NPR1, and SA-dependent signaling.

Phosphorus (P) is a quintessential macronutrient utilized by plants to support various metabolic processes during growth and development. Recent studies have revealed the pivotal role of inositol hexa-kis/pyrophosphate (InsP6-8), the derivatives of Myo-inositol (MI), in facilitating the interaction between SYG1/PHO81/XPR1 (SPX) and Phosphate starvation response (PHR) proteins. Myo-inositol phosphate synthase (MIPS) catalyzes the first committed step in MI biosynthesis. Although the role of MIPS genes in mediating stress responses in plants is well elucidated, its role in phosphate (Pi) deficiency remains largely unexplored. This study demonstrates that out of the five MIPS genes encoded by the tomato genome, only SlMIPS2 is sharply induced at an early stage of Pi starvation in tomato seedlings. Silencing of SlMIPS2 led to improved seedling growth with enhanced total soluble Pi and total P levels in the silenced plants under high Pi availability. SlMIPS2 silencing also caused a significant reduction in MI and InsP6 content in the tomato seedlings. These seedlings with depleted InsP6 levels accumulated lower levels of SlSPX2 protein. In contrast, stabilized SlPHL1 levels were noticed in these plants, directly implicating this transcription factor in activating phosphate starvation inducible (PSI) genes in the SlMIPS2-silenced seedlings, even under high Pi conditions. The results assign a novel role to SlMIPS2 in regulating cellular InsP6 levels and SPX-PHR interactions to control Pi homeostasis in tomato seedlings.

The future sustainability of viticulture depends on the development of grapevine cultivars with genetic resistance to diseases such as powdery mildew, downy mildew, and Pierce's disease. Recent advances in grape and pathogen genomics have dramatically improved our approach to durable disease resistance. The availability of diploid genome references for wild species, combined with the ability to phase resistance haplotypes and conduct genome-wide association and expression analyses, has greatly enhanced our ability to dissect genetic resistance loci. This progress is yielding candidate genes that will form the foundation for precise breeding, gene stacking, and genome editing in grape improvement programs. As resistance genes are deployed in vineyards, pathogen populations evolve to adapt and evade these defenses, posing ongoing challenges. Understanding the adaptive mechanisms of grapevine pathogens in response to resistant cultivars is crucial. Grape pathogenomics is advancing rapidly, marked by the sequencing of many pathogen genomes, the discovery of effectors, including the first ones responsible for disease resistance breakdown, and the development of graph-based pangenomes. These advancements offer valuable insights into pathogen evolution and inform strategies for sustainable disease management. Together, these genomic tools and insights are paving the way for developing resilient grapevine varieties, ensuring the long-term sustainability of viticulture.

Frankia cluster-2 strains are diazotrophs that engage in root nodule symbiosis with actinorhizal plants of the Cucurbitales and the Rosales. Previous studies have shown that an assimilated nitrogen source, presumably arginine, is exported to the host in nodules of Datisca glomerata (Cucurbitales), while a different metabolite is exported in the nodules of Ceanothus thyrsiflorus (Rosales). To investigate if an assimilated nitrogen form is commonly exported to the host by cluster-2 strains, and which metabolite would be exported in Ceanothus, we analysed gene expression levels, metabolite profiles, and enzyme activities in nodules. We conclude that the export of assimilated nitrogen in symbiosis seems to be a common feature for Frankia cluster-2 strains, but which source is host-dependent. The export of assimilated ammonium to the host suggests that 2-oxoglutarate is drawn from the TCA cycle at a high rate. This specialised metabolism obviates the need for the reductive branch of the TCA cycle. We found several genes encoding enzymes of the central carbon and nitrogen metabolism were lacking in Frankia cluster-2 genomes: the glyoxylate shunt and succinate semialdehyde dehydrogenase. This led to a linearization of the TCA cycle, and we hypothesize this could explain the low saprotrophic potential of Frankia cluster-2.

Trichomes are specialized hair-like structures in the epidermal cells of the above-ground parts of plants and help to protect them from pests and pathogens, and produce valuable metabolites. Chrysanthemum morifolium, which is used in tea products, has both ornamental and medicinal value; however, it is susceptible to infection by the fungus Alternaria alternata, which can result in substantial economic losses. Increasing the density of glandular trichomes enhances disease resistance and improves the production of medicinal metabolites in chrysanthemums, and jasmonate (JA) is known to promote the formation of trichomes in various plants. However, it remains unclear whether glandular trichomes in chrysanthemums are regulated by JA. In addition, grafting, a technique that can improve plant resistance to biotic stresses, has been poorly examined for its impact on glandular trichomes, terpenoids, and disease resistance. In this study, we demonstrate that grafting with Artemisia vulgaris rootstocks improves the resistance of chrysanthemum scions to A. alternata. Heterografted chrysanthemums exhibited higher trichome density and terpenoid content compared to self-grafted counterparts. Transcriptome analysis highlighted the significant role of CmJAZ1-like in disease resistance in heterografted chrysanthemums. Lines overexpressing CmJAZ1-like exhibited sensitivity to A. alternata, and this was characterized by reduced glandular trichome density and limited terpenoid content. Conversely, CmJAZ1-like silenced lines exhibited resistance to A. alternata and showed increased glandular trichome density and terpenoid content. Higher JA content was found in the heterografted chrysanthemum scions compared to self-grafted ones. Furthermore, we established that JA promoted the development of glandular trichomes and the synthesis of terpenoids while also inducing the degradation of CmJAZ1-like proteins in chrysanthemums. Our findings suggest that higher JA increases trichome density and terpenoid content, thereby enhancing resistance to A. alternata by regulating CmJAZ1-like in heterografted chrysanthemums.

Successful plant reproduction depends on the adequate development of floral organs controlled by cell proliferation and other processes. The Stigma/style cell-cycle inhibitor 1 (SCI1) gene regulates cell proliferation and affects the final size of the female reproductive organ. To unravel the molecular mechanism exerted by Nicotiana tabacum SCI1 in cell proliferation control, we searched for its interaction partners through semi-in vivo pull-down experiments, uncovering a cyclin-dependent kinase, NtCDKG;2. Bimolecular fluorescence complementation and co-localization experiments showed that SCI1 interacts with NtCDKG;2 and its cognate NtCyclin L in nucleoli and splicing speckles. The screening of a yeast two-hybrid cDNA library using SCI1 as bait revealed a novel DEAD-box RNA helicase (NtRH35). Interaction between the NtCDKG;2-NtCyclin L complex and NtRH35 is also shown. Subcellular localization experiments showed that SCI1, NtRH35, and the NtCDKG;2-NtCyclin L complex associate with each other within splicing speckles. The yeast two-hybrid screening of NtCDKG;2 and NtRH35 identified the conserved spliceosome components U2a', NF-κB activating protein (NKAP), and CACTIN. This work presents SCI1 and its interactors, the NtCDKG;2-NtCyclin L complex and NtRH35, as new spliceosome-associated proteins. Our findings reveal a network of interactions and indicate that SCI1 may regulate cell proliferation through the splicing process, providing new insights into the intricate molecular pathways governing plant development.

Understanding the spatial organization of genomes within chromatin is crucial for deciphering gene regulation. A recently developed CRISPR-dCas9-based genome labeling tool, known as CRISPR-FISH, allows efficient labeling of repetitive sequences. Unlike standard fluorescence in situ hybridization (FISH), CRISPR-FISH eliminates the need for global DNA denaturation, allowing for superior preservation of chromatin structure. Here, we report on further development of the CRISPR-FISH method, which has been enhanced for increased efficiency through the engineering of a recombinant dCas9 protein containing an ALFA-tag. Using an ALFA-tagged dCas9 protein assembled with an Arabidopsis centromere-specific guide RNA, we demonstrate target-specific labeling with a fluorescence-labeled NbALFA nanobody. The dCas9 protein possessing multiple copies of the ALFA-tag, in combination with a minibody and fluorescence-labeled anti-rabbit secondary antibody, resulted in enhanced target-specific signals. The dCas9-ALFA-tag system was also instrumental in live cell imaging of telomeres in Nicotiana benthamiana. This method will further expand the CRISPR imaging toolkit, facilitating a better understanding of genome organization. Furthermore, we report the successful integration of the highly sensitive tyramide signal amplification method with CRISPR-FISH, demonstrating effective labeling of Arabidopsis centromeres.

Plant viruses exist in a broader ecological community that includes non-vector herbivores that can impact vector abundance, behavior, and virus transmission within shared host plants. However, little is known about the effects of non-vector herbivore infestation on virus transmission by vector insects on neighboring plants through inter-plant airborne chemicals. In this study, we investigated how volatiles emitted from tomato plants infested with the two-spotted spider mite (Tetranychus urticae) affect the infection of neighboring plants by tomato yellow leaf curl virus (TYLCV) transmitted by whitefly (Bemisia tabaci). Exposure of neighboring tomato plants to volatiles released from T. urticae-infested tomato plants reduced subsequent herbivory as well as TYLCV transmission and infection, and the jasmonic acid signaling pathway was essential for generation of the inter-plant defense signals. We also demonstrated that (E)-β-ocimene and methyl salicylic acid were two volatiles induced by T. urticae that synergistically attenuated TYLCV transmission and infection in tomato. Thus, our findings suggest that plant-plant communication via volatiles likely represents a widespread defensive mechanism that substantially contributes to plant fitness. Understanding such phenomena may help us to predict the occurrence and epidemics of multiple herbivores and viruses in agroecosystems, and ultimately to manage pest and virus outbreaks.