Injury Activates Ca2+/Calmodulin-Dependent Phosphorylation of JAV1-JAZ8-WRKY51 Complex for Jasmonate Biosynthesis.

Insect herbivory causes severe damage to plants and threatens the world's food production. During evolutionary adaptation, plants have evolved sophisticated mechanisms to rapidly accumulate a key defense hormone, jasmonate (JA), that triggers plant defense against herbivory. However, little is known about how plants initially activate JA biosynthesis at encounter with herbivory. Here, we uncover that a novel JAV1-JAZ8-WRKY51 (JJW) complex controls JA biosynthesis to defend against insect attack. In healthy plants, the JJW complex represses JA biosynthesis to restrain JA at a low basal level to ensure proper plant growth. When plants are injured by insect attack, injury rapidly triggers calcium influxes to activate calmodulin-dependent phosphorylation of JAV1, which disintegrates JJW complex and activates JA biosynthesis, giving rise to the rapid burst of JA for plant defense. Our findings offer new insights into the highly sophisticated defense systems evolved by plants to defend against herbivory.

Jasmonate-based warfare between the pathogenic intruder and host plant: who wins?

Plants and microbial pathogens often engage in a fierce war that determines their survival. Host plants have evolved sophisticated regulatory mechanisms to fine-tune defense responses to counter attacks from pathogens, while pathogens often hijack the lipid-derived phytohormone jasmonate to cause hormonal signaling imbalances for efficient infection. This review focuses on the jasmonate-based warfare between host plants and pathogenic intruders, and further discusses approaches to uncouple plant growth and defense tradeoffs in crop breeding.

Physiological and transcriptomic analysis reveal the regulatory mechanism underlying grain quality improvement induced by rice ratooning.

BACKGROUND: Ratoon rice cropping has been introduced for increased rice production in southern China and, as a result, has been becoming increasingly popular. However, only a few studies have addressed the regulatory mechanism underlying grain quality improvement induced by rice ratooning. RESULTS: In this study, parameters of rice quality, including head rice yield, chalky grain percentage, grain chalkiness degree, hardness and taste value, were shown to be much improved in the ratooning season rice as compared to its counterparts main and late cropping season rice, indicating that such an improvement was irrespective of seasonal effects. In addition, the nutritional components of grains varied greatly between main-cropping season rice, ratooning season rice and late-cropping season rice and displayed a significant correlation with rice quality. Finally, the regulatory mechanism underlying rice quality improvement revealed that gibberellin-dominated regulation and plant hormone signal transduction jointly contributed to a decrease in formation of chalky grains. CONCLUSION: This work improves our knowledge on rice quality improvement under rice ratooning, particularly on the regulatory mechanism of plant hormones. © 2022 Society of Chemical Industry.

Strigolactone mimic 2-nitrodebranone is highly active in Arabidopsis growth and development.

Strigolactones play crucial roles in regulating plant architecture and development, as endogenous hormones, and orchestrating symbiotic interactions with fungi and parasitic plants, as components of root exudates. rac-GR24 is currently the most widely used strigolactone analog and serves as a reference compound in investigating the action of strigolactones. In this study, we evaluated a suite of debranones and found that 2-nitrodebranone (2NOD) exhibited higher biological activity than rac-GR24 in various aspects of plant growth and development in Arabidopsis, including hypocotyl elongation inhibition, root hair promotion and senescence acceleration. The enhanced activity of 2NOD in promoting AtD14-SMXL7 and AtD14-MAX2 interactions indicates that the molecular structure of 2NOD is a better match for the ligand perception site pocket of D14. Moreover, 2NOD showed lower activity than rac-GR24 in promoting Orobanche cumana seed germination, suggesting its higher ability to control plant architecture than parasitic interactions. In combination with the improved stability of 2NOD, these results demonstrate that 2NOD is a strigolactone analog that can specifically mimic the activity of strigolactones and that 2NOD exhibits strong potential as a tool for studying the strigolactone signaling pathway in plants.

Molecular basis for high ligand sensitivity and selectivity of strigolactone receptors in Striga.

Seeds of the root parasitic plant Striga hermonthica can sense very low concentrations of strigolactones (SLs) exuded from host roots. The S. hermonthica hyposensitive to light (ShHTL) proteins are putative SL receptors, among which ShHTL7 reportedly confers sensitivity to picomolar levels of SL when expressed in Arabidopsis thaliana. However, the molecular mechanism underlying ShHTL7 sensitivity is unknown. Here we determined the ShHTL7 crystal structure and quantified its interactions with various SLs and key interacting proteins. We established that ShHTL7 has an active-site pocket with broad-spectrum response to different SLs and moderate affinity. However, in contrast to other ShHTLs, we observed particularly high affinity of ShHTL7 for F-box protein AtMAX2. Furthermore, ShHTL7 interacted with AtMAX2 and with transcriptional regulator AtSMAX1 in response to nanomolar SL concentration. ShHTL7 mutagenesis analyses identified surface residues that contribute to its high-affinity binding to AtMAX2 and residues in the ligand binding pocket that confer broad-spectrum response to SLs with various structures. Crucially, yeast-three hybrid experiments showed that AtMAX2 confers responsiveness of the ShHTL7-AtSMAX1 interaction to picomolar levels of SL in line with the previously reported physiological sensitivity. These findings highlight the key role of SL-induced MAX2-ShHTL7-SMAX1 complex formation in determining the sensitivity to SL. Moreover, these data suggest a strategy to screen for compounds that could promote suicidal seed germination at physiologically relevant levels.

DWARF14 is a non-canonical hormone receptor for strigolactone.

Classical hormone receptors reversibly and non-covalently bind active hormone molecules, which are generated by biosynthetic enzymes, to trigger signal transduction. The α/ß hydrolase DWARF14 (D14), which hydrolyses the plant branching hormone strigolactone and interacts with the F-box protein D3/MAX2, is probably involved in strigolactone detection. However, the active form of strigolactone has yet to be identified and it is unclear which protein directly binds the active form of strigolactone, and in which manner, to act as the genuine strigolactone receptor. Here we report the crystal structure of the strigolactone-induced AtD14-D3-ASK1 complex, reveal that Arabidopsis thaliana (At)D14 undergoes an open-to-closed state transition to trigger strigolactone signalling, and demonstrate that strigolactone is hydrolysed into a covalently linked intermediate molecule (CLIM) to initiate a conformational change of AtD14 to facilitate interaction with D3. Notably, analyses of a highly branched Arabidopsis mutant d14-5 show that the AtD14(G158E) mutant maintains enzyme activity to hydrolyse strigolactone, but fails to efficiently interact with D3/MAX2 and loses the ability to act as a receptor that triggers strigolactone signalling in planta. These findings uncover a mechanism underlying the allosteric activation of AtD14 by strigolactone hydrolysis into CLIM, and define AtD14 as a non-canonical hormone receptor with dual functions to generate and sense the active form of strigolactone.

JAV1 controls jasmonate-regulated plant defense.

Plants evolve effective mechanisms to protect themselves from environmental stresses and employ jasmonates as vital defense signals to defend against insect attack and pathogen infection. Jasmonates are also recognized as an essential growth regulator by which diverse developmental processes are mediated. Despite substantial research, there are no key signaling components reported yet to control jasmonate-regulated plant defense independent of developmental responses. We identify JAV1, a key gene in the jasmonate pathway, which functions as a negative regulator to control plant defense but does not play a detectable role in plant development. Our results suggest that when encountering insect attack and pathogen infection, plants accumulate jasmonates that trigger JAV1 degradation via the 26S proteasome to activate defensive gene expression and elevate resistances against both insects and pathogens. These findings have provided insight into the molecular mechanism by which plants integrate jasmonate signals to protect themselves from insect attack and pathogen infection.

POSTAR2: deciphering the post-transcriptional regulatory logics.

Post-transcriptional regulation of RNAs is critical to the diverse range of cellular processes. The volume of functional genomic data focusing on post-transcriptional regulation logics continues to grow in recent years. In the current database version, POSTAR2 (http://lulab.life.tsinghua.edu.cn/postar), we included the following new features and data: updated ∼500 CLIP-seq datasets (∼1200 CLIP-seq datasets in total) from six species, including human, mouse, fly, worm, Arabidopsis and yeast; added a new module 'Translatome', which is derived from Ribo-seq datasets and contains ∼36 million open reading frames (ORFs) in the genomes from the six species; updated and unified post-transcriptional regulation and variation data. Finally, we improved web interfaces for searching and visualizing protein-RNA interactions with multi-layer information. Meanwhile, we also merged our CLIPdb database into POSTAR2. POSTAR2 will help researchers investigate the post-transcriptional regulatory logics coordinated by RNA-binding proteins and translational landscape of cellular RNAs.

The DELLA proteins interact with MYB21 and MYB24 to regulate filament elongation in Arabidopsis.

BACKGROUND: Gibberellin (GA) and jasmonate (JA) are two essential phytohormones for filament elongation in Arabidopsis. GA and JA trigger degradation of DELLAs and JASMONATE ZIM-domain (JAZ) proteins through SCFSLY1 and SCFCOI1 separately to activate filament elongation. In JA pathway, JAZs interact with MYB21 and MYB24 to control filament elongation. However, little is known how DELLAs regulate filament elongation. RESULTS: Here we showed that DELLAs interact with MYB21 and MYB24, and that R2R3 domains of MYB21 and MYB24 are responsible for interaction with DELLAs. Furthermore, we demonstrated that DELLA and JAZ proteins coordinately repress the transcriptional function of MYB21 and MYB24 to inhibit filament elongation. CONCLUSION: We discovered that DELLAs interact with MYB21 and MYB24, and that DELLAs and JAZs attenuate the transcriptional function of MYB21 and MYB24 to control filament elongation. This study reveals a novel cross-talk mechanism of GA and JA in the regulation of filament elongation in Arabidopsis.

Variation in the regulatory region of FZP causes increases in secondary inflorescence branching and grain yield in rice domestication.

Inflorescence branching is a key agronomic trait determining rice yield. The primary branch of the ancestral wild rice (Oryza rufipogon Griff.) bears few grains, due to minimal secondary branching. By contrast, Oryza sativa cultivars have been selected to produce large panicles with more secondary branches. Here we showed that the CONTROL OF SECONDARY BRANCH 1 (COS1) gene, which is identical to FRIZZY PANICLE (FZP), plays an important role in the key transition from few secondary branches in wild rice to more secondary branches in domesticated rice cultivars. A 4-bp tandem repeat deletion approximately 2.7 kb upstream of FZP may affect the binding activities of auxin response factors to the FZP promoter, decrease the expression level of FZP and significantly enhance the number of secondary branches and grain yield in cultivated rice. Functional analyses showed that NARROW LEAF 1 (NAL1), a trypsin-like serine and cysteine protease, interacted with FZP and promoted its degradation. Consistently, downregulating FZP expression or upregulating NAL1 expression in the commercial cultivar Zhonghua 17 increased the number of secondary branches per panicle, grain number per panicle and grain yield per plant. Our findings not only provide insights into the molecular mechanism of increasing grain number and yield during rice domestication, but also offer favorable genes for improving the grain yield of rice.

Jasmonate action in plant defense against insects.

Herbivorous insects represent one of the major threats to sessile plants. To cope with herbivore challenges, plants have evolved sophisticated defense systems, in which the lipid-derived phytohormone jasmonate plays a crucial role. Perception of insect attack locally and systemically elicits rapid synthesis of jasmonate, which is perceived by the F-box protein COI1 to further recruit JAZ repressors for ubiquitination and degradation, thereby releasing transcription factors that subsequently activate plant defense against insect attack. Here, we review recent progress in understanding the molecular basis of jasmonate action in plant defense against insects.

GAD1 Encodes a Secreted Peptide That Regulates Grain Number, Grain Length, and Awn Development in Rice Domestication.

Cultivated rice (Oryza sativa) was domesticated from wild rice (Oryza rufipogon), which typically displays fewer grains per panicle and longer grains than cultivated rice. In addition, wild rice has long awns, whereas cultivated rice has short awns or lacks them altogether. These changes represent critical events in rice domestication. Here, we identified a major gene, GRAIN NUMBER, GRAIN LENGTH AND AWN DEVELOPMENT1 (GAD1), that regulates those critical changes during rice domestication. GAD1 is located on chromosome 8 and is predicted to encode a small secretary signal peptide belonging to the EPIDERMAL PATTERNING FACTOR-LIKE family. A frame-shift insertion in gad1 destroyed the conserved cysteine residues of the peptide, resulting in a loss of function, and causing the increased number of grains per panicle, shorter grains, and awnless phenotype characteristic of cultivated rice. Our findings provide a useful paradigm for revealing functions of peptide signal molecules in plant development and helps elucidate the molecular basis of rice domestication.

Efficient ASK-assisted system for expression and purification of plant F-box proteins.

Ubiquitin-mediated protein degradation plays an essential role in plant growth and development as well as responses to environmental and endogenous signals. F-box protein is one of the key components of the SCF (SKP1-CUL1-F-box protein) E3 ubiquitin ligase complex, which recruit specific substrate proteins for subsequent ubiquitination and 26S proteasome-mediated degradation to regulate developmental processes and signaling networks. However, it is not easy to obtain purified F-box proteins with high activity due to their unstable protein structures. Here, we found that Arabidopsis SKP-like proteins (ASKs) can significantly improve soluble expression of F-box proteins and maintain their bioactivity. We established an efficient ASK-assisted method to express and purify plant F-box proteins. The method meets a broad range of criteria required for the biochemical analysis or protein crystallization of plant F-box proteins.

CLCuMuB ßC1 Subverts Ubiquitination by Interacting with NbSKP1s to Enhance Geminivirus Infection in Nicotiana benthamiana.

Viruses interfere with and usurp host machinery and circumvent defense responses to create a suitable cellular environment for successful infection. This is usually achieved through interactions between viral proteins and host factors. Geminiviruses are a group of plant-infecting DNA viruses, of which some contain a betasatellite, known as DNAß. Here, we report that Cotton leaf curl Multan virus (CLCuMuV) uses its sole satellite-encoded protein ßC1 to regulate the plant ubiquitination pathway for effective infection. We found that CLCuMu betasatellite (CLCuMuB) ßC1 interacts with NbSKP1, and interrupts the interaction of NbSKP1s with NbCUL1. Silencing of either NbSKP1s or NbCUL1 enhances the accumulation of CLCuMuV genomic DNA and results in severe disease symptoms in plants. ßC1 impairs the integrity of SCFCOI1 and the stabilization of GAI, a substrate of the SCFSYL1 to hinder responses to jasmonates (JA) and gibberellins (GA). Moreover, JA treatment reduces viral accumulation and symptoms. These results suggest that CLCuMuB ßC1 inhibits the ubiquitination function of SCF E3 ligases through interacting with NbSKP1s to enhance CLCuMuV infection and symptom induction in plants.

Rice DWARF14 acts as an unconventional hormone receptor for strigolactone.

Strigolactones (SLs) act as an important class of phytohormones to regulate plant shoot branching, and also serve as rhizosphere signals to mediate interactions of host plants with soil microbes and parasitic weeds. SL receptors in dicots, such as DWARF14 in Arabidopsis (AtD14), RMS3 in pea, and ShHTL7 in Striga, serve as unconventional receptors that hydrolyze SLs into a D-ring-derived intermediate CLIM and irreversibly bind CLIM to trigger SL signal transduction. Here, we show that D14 from the monocot rice can complement Arabidopsis d14 mutant and interact with the SL signaling components in Arabidopsis. Our results further reveal that rice D14, similar to SL receptors in dicots, also serves as an unconventional hormone receptor that generates and irreversibly binds the active form of SLs. These findings uncover the conserved functions of D14 proteins in monocots and dicots.

Regulation of Jasmonate-Mediated Stamen Development and Seed Production by a bHLH-MYB Complex in Arabidopsis.

Stamens are the plant male reproductive organs essential for plant fertility. Proper development of stamens is modulated by environmental cues and endogenous hormone signals. Deficiencies in biosynthesis or perception of the phytohormone jasmonate (JA) attenuate stamen development, disrupt male fertility, and abolish seed production in Arabidopsis thaliana. This study revealed that JA-mediated stamen development and seed production are regulated by a bHLH-MYB complex. The IIIe basic helix-loop-helix (bHLH) transcription factor MYC5 acts as a target of JAZ repressors to function redundantly with other IIIe bHLH factors such as MYC2, MYC3, and MYC4 in the regulation of stamen development and seed production. The myc2 myc3 myc4 myc5 quadruple mutant exhibits obvious defects in stamen development and significant reduction in seed production. Moreover, these IIIe bHLH factors interact with the MYB transcription factors MYB21 and MYB24 to form a bHLH-MYB transcription complex and cooperatively regulate stamen development. We speculate that the JAZ proteins repress the bHLH-MYB complex to suppress stamen development and seed production, while JA induces JAZ degradation and releases the bHLH-MYB complex to subsequently activate the expression of downstream genes essential for stamen development and seed production.

Regulation of Jasmonate-Induced Leaf Senescence by Antagonism between bHLH Subgroup IIIe and IIId Factors in Arabidopsis.

Plants initiate leaf senescence to relocate nutrients and energy from aging leaves to developing tissues or storage organs for growth, reproduction, and defense. Leaf senescence, the final stage of leaf development, is regulated by various environmental stresses, developmental cues, and endogenous hormone signals. Jasmonate (JA), a lipid-derived phytohormone essential for plant defense and plant development, serves as an important endogenous signal to activate senescence-associated gene expression and induce leaf senescence. This study revealed one of the mechanisms underlying JA-induced leaf senescence: antagonistic interactions of the bHLH subgroup IIIe factors MYC2, MYC3, and MYC4 with the bHLH subgroup IIId factors bHLH03, bHLH13, bHLH14, and bHLH17. We showed that MYC2, MYC3, and MYC4 function redundantly to activate JA-induced leaf senescence. MYC2 binds to and activates the promoter of its target gene SAG29 (SENESCENCE-ASSOCIATED GENE29) to activate JA-induced leaf senescence. Interestingly, plants have evolved an elaborate feedback regulation mechanism to modulate JA-induced leaf senescence: The bHLH subgroup IIId factors (bHLH03, bHLH13, bHLH14, and bHLH17) bind to the promoter of SAG29 and repress its expression to attenuate MYC2/MYC3/MYC4-activated JA-induced leaf senescence. The antagonistic regulation by activators and repressors would mediate JA-induced leaf senescence at proper level suitable for plant survival in fluctuating environmental conditions.

MYC5 is Involved in Jasmonate-Regulated Plant Growth, Leaf Senescence and Defense Responses.

Jasmonates (JAs), lipid-derived phytohormones, regulate plant growth, development and defenses against biotic stresses. CORONATINE INSENSITIVE1 perceives bioactive JA and recruits JASMONATE ZIM-DOMAIN (JAZ) proteins for ubiquitination and subsequent degradation via the 26S proteasome, which de-represses JAZ-targeted transcription factors that regulate diverse JA responses. Recent studies showed that the Arabidopsis basic helix-loop-helix transcription factor MYC5 interacts with JAZs and regulates stamen development. However, whether MYC5 mediates other JA responses is unclear. Here, we show that MYC5 functions redundantly with MYC2, MYC3 and MYC4 to modulate JA-regulated root growth inhibition and plant defenses against insect attack and pathogen infection, and that it positively regulates JA-induced leaf senescence. Our findings define MYC5 as an important regulator that is essential for diverse JA responses.

Endogenous Bioactive Jasmonate Is Composed of a Set of (+)-7-iso-JA-Amino Acid Conjugates.

Jasmonates (JAs) regulate a wide range of plant defense and development processes. The bioactive JA is perceived by its receptor COI1 to trigger the degradation of JASMONATE ZIM-DOMAIN (JAZ) proteins and subsequently derepress the JAZ-repressed transcription factors for activation of expression of JA-responsive genes. So far, (+)-7-iso-JA-l-Ile has been the only identified endogenous bioactive JA molecule. Here, we designed coronafacic acid (CFA) conjugates with all the amino acids (CFA-AA) to mimic the JA amino acid conjugates, and revealed that (+)-7-iso-JA-Leu, (+)-7-iso-JA-Val, (+)-7-iso-JA-Met, and (+)-7-iso-JA-Ala are new endogenous bioactive JA molecules. Furthermore, our studies uncover the general characteristics for all the bioactive JA molecules, and provide a new strategy to synthetically generate novel active JA molecules.