Regulation of floral senescence in Arabidopsis by coordinated action of CONSTANS and jasmonate signaling

Study on the effect of the chiral herbicide imazethapyr on flowering initiation in Arabidopsis thaliana

Non-target plants play a key role in maintaining ecological balance and biodiversity. Here, we studied the effect of the chiral herbicide imazethapyr (IM) on the flowering initiation of the non-target plant Arabidopsis thaliana and its underlying mechanism. Plants treated with R-IM initiated flowering earlier than those treated with S-IM. The herbicidally active R-IM had a much greater effect on various phytohormones than S-IM, and this effect increased with the concentration of R-IM. Before flowering, R-IM had a significant effect on the internal levels of 1-aminocyclopropane-1-carboxylic acid (ACC), indole-3-acetic acid (IAA), abscisic acid (ABA), and gibberellic acid (GA3) in Arabidopsis plants, which indicated that it promoted the production of ACC, and high concentrations of R-IM also promoted IAA, ABA, and GA3. R-IM promoted ACC, IAA, and GA3 before and during flowering. High concentrations of R-IM strongly promoted IAA and inhibited GA3, and R-IM inhibited or promoted ACC depending on the concentrations applied. Thus, earlier flowering of Arabidopsis under R-IM treatment may be affected by phytohormone levels throughout the plant, and IAA, ACC, and GA3 likely have significant effects on flowering.

The SnRK2.2-ZmHsf28-JAZ14/17 module regulates drought tolerance in maize

Abscisic acid (ABA) and jasmonic acid (JA) are important plant hormones in response to drought stress. We have identified that ZmHsf28 elevated ABA and JA accumulation to confer drought tolerance in maize; however, the underlying mechanism still remains elusive. The knockout line zmhsf28 is generated to confirm the positive role of ZmHsf28 in drought response. Multiple approaches are combined to reveal protein interaction among ZmHsf28, ZmSnRK2.2 and ZmJAZ14/17, which form a regulatory module to mediate maize drought tolerance through regulating ABA and JA key biosynthetic genes ZmNCED3 and ZmLOX8. Upon drought stress, zmhsf28 plants exhibit weaker tolerance than the WT plants with slower stomatal closure and more reactive oxygen species accumulation. ZmHsf28 interacted with ZmSnRK2.2 physically, resulting in phosphorylation at Ser220, which enhances binding to the heat shock elements of ZmNECD3 and ZmLOX8 promoters and subsequent gene expression. Meanwhile, ZmMYC2 upregulates ZmHsf28 gene expression through acting on the G-box of its promoter. Besides, ZmJAZ14/17 competitively interact with ZmHsf28 to interfere with protein interaction between ZmHsf28 and ZmSnRK2.2, blocking ZmHsf28 phosphorylation and impairing downstream gene regulation. The ZmSnRK2.2-ZmHsf28-ZmJAZ14/17 module is identified to regulate drought tolerance through coordinating ABA and JA signaling, providing the insights for breeding to improve drought resistance in maize.

More than flowering: CONSTANS plays multifaceted roles in plant development and stress responses

Plants have evolved a remarkable ability to sense and respond to changes in photoperiod, allowing adjustments to their growth and development based on seasonal and environmental cues. The floral transition is a pivotal stage in plant growth and development, signifying a shift from vegetative to reproductive growth. CONSTANS (CO), a central photoperiodic response factor conserved in various plants, mediates day-length signals to control the floral transition, although its mechanisms of action vary among plants with different day-length requirements. In addition, recent studies have uncovered roles for CO in organ development and stress responses. These pleiotropic roles in model plants and crops make CO a potentially fruitful target for molecular breeding aimed at modifying crop agronomic traits. This review systematically traces research on CO, from its discovery and functional studies to the exploration of its regulatory mechanisms and newly discovered functions, providing important insight into the roles of CO and laying a foundation for future research.

Genome-Wide Identification and Expression Analysis of the COL Gene Family in Hemerocallis citrina Baroni

Hemerocallis citrina Baroni (H. citrina) is an important specialty vegetable that is not only edible and medicinal but also has ornamental value. However, much remains unknown about the regulatory mechanisms associated with the growth, development, and flowering rhythm of this plant. CO, as a core regulatory factor in the photoperiod pathway, coordinates light and circadian clock inputs to transmit flowering signals. We identified 18 COL genes (HcCOL1-HcCOL18) in the H. citrina cultivar 'Mengzihua' and studied their chromosomal distribution, phylogenetic relationships, gene and protein structures, collinearity, and expression levels in the floral organs at four developmental stages. The results indicate that these genes can be classified into three groups based on phylogenetic analysis. The major expansion of the HcCOL gene family occurred via segmental duplication, and the Ka/Ks ratio indicated that the COL genes of Arabidopsis thaliana, Oryza sativa, Phalaenopsis equestris, and H. citrina were under purifying selection. Many cis-elements, including light response elements, abiotic stress elements, and plant hormone-inducible elements, were distributed in the promoter sequences of the HcCOL genes. Expression analysis of HcCOL genes at four floral developmental stages revealed that most of the HcCOL genes were expressed in floral organs and might be involved in the growth, development, and senescence of the floral organs of H. citrina. This study lays a foundation for the further elucidation of the function of the HcCOL gene in H. citrina and provides a theoretical basis for the molecular design breeding of H. citrina.

CONSTANS alters the circadian clock in Arabidopsis thaliana

Plants are sessile organisms that have acquired highly plastic developmental strategies to adapt to the environment. Among these processes, the floral transition is essential to ensure reproductive success and is finely regulated by several internal and external genetic networks. The photoperiodic pathway, which controls plant response to day length, is one of the most important pathways controlling flowering. In Arabidopsis photoperiodic flowering, CONSTANS (CO) is the central gene activating the expression of the florigen FLOWERING LOCUS T (FT) in the leaves at the end of a long day. The circadian clock strongly regulates CO expression. However, to date, no evidence has been reported regarding a feedback loop from the photoperiod pathway back to the circadian clock. Using transcriptional networks, we have identified relevant network motifs regulating the interplay between the circadian clock and the photoperiod pathway. Gene expression, chromatin immunoprecipitation experiments, and phenotypic analysis allowed us to elucidate the role of CO over the circadian clock. Plants with altered CO expression showed a different internal clock period, measured by daily leaf rhythmic movements. We showed that CO upregulates the expression of key genes related to the circadian clock, such as CCA1, LHY, PRR5, and GI, at the end of a long day by binding to specific sites on their promoters. Moreover, a high number of PRR5-repressed target genes are upregulated by CO, and this could explain the phase transition promoted by CO. The CO-PRR5 complex interacts with the bZIP transcription factor HY5 and helps to localize the complex in the promoters of clock genes. Taken together, our results indicate that there may be a feedback loop in which CO communicates back to the circadian clock, providing seasonal information to the circadian system.

Exploring the effects of red light night break on the defence mechanisms of tomato against fungal pathogen Botrytis cinerea

Plant infections caused by fungi lead to significant crop losses worldwide every year. This study aims to better understand the plant defence mechanisms regulated by red light, in particular, the effects of red light at night when most phytopathogens are highly infectious. Our results showed that superoxide production significantly increased immediately after red light exposure and, together with hydrogen peroxide levels, was highest at dawn after 30 min of nocturnal red-light treatment. In parallel, red-light-induced expression and increased the activities of several antioxidant enzymes. The nocturnal red light did not affect salicylic acid but increased jasmonic acid levels immediately after illumination, whereas abscisic acid levels increased 3 h after nocturnal red-light exposure at dawn. Based on the RNAseq data, red light immediately increased the transcription of several chloroplastic chlorophyll a-b binding protein and circadian rhythm-related genes, such as Constans 1, CONSTANS interacting protein 1 and zinc finger protein CONSTANS-LIKE 10. In addition, the levels of several transcription factors were also increased after red light exposure, such as the DOF zinc finger protein and a MYB transcription factor involved in the regulation of circadian rhythms and defence responses in tomato. In addition to identifying these key transcription factors in tomato, the application of red light at night for one week not only reactivated key antioxidant enzymes at the gene and enzyme activity level at dawn but also contributed to a more efficient and successful defence against Botrytis cinerea infection.

CONSTANS, a HUB for all seasons: How photoperiod pervades plant physiology regulatory circuits

How does a plant detect the changing seasons and make important developmental decisions accordingly? How do they incorporate daylength information into their routine physiological processes? Photoperiodism, or the capacity to measure the daylength, is a crucial aspect of plant development that helps plants determine the best time of the year to make vital decisions, such as flowering. The protein CONSTANS (CO) constitutes the central regulator of this sensing mechanism, not only activating florigen production in the leaves but also participating in many physiological aspects in which seasonality is important. Recent discoveries place CO in the center of a gene network that can determine the length of the day and confer seasonal input to aspects of plant development and physiology as important as senescence, seed size, or circadian rhythms. In this review, we discuss the importance of CO protein structure, function, and evolutionary mechanisms that embryophytes have developed to incorporate annual information into their physiology.

Dissection of the IDA promoter identifies WRKY transcription factors as abscission regulators in Arabidopsis

Plants shed organs such as leaves, petals, or fruits through the process of abscission. Monitoring cues such as age, resource availability, and biotic and abiotic stresses allow plants to abscise organs in a timely manner. How these signals are integrated into the molecular pathways that drive abscission is largely unknown. The INFLORESCENCE DEFICIENT IN ABSCISSION (IDA) gene is one of the main drivers of floral organ abscission in Arabidopsis and is known to transcriptionally respond to most abscission-regulating cues. By interrogating the IDA promoter in silico and in vitro, we identified transcription factors that could potentially modulate IDA expression. We probed the importance of ERF- and WRKY-binding sites for IDA expression during floral organ abscission, with WRKYs being of special relevance to mediate IDA up-regulation in response to biotic stress in tissues destined for separation. We further characterized WRKY57 as a positive regulator of IDA and IDA-like gene expression in abscission zones. Our findings highlight the promise of promoter element-targeted approaches to modulate the responsiveness of the IDA signaling pathway to harness controlled abscission timing for improved crop productivity.

Transcription factors NtNAC028 and NtNAC080 form heterodimers to regulate jasmonic acid biosynthesis during leaf senescence in Nicotiana tabacum

Plant senescence, as a highly integrated developmental stage, involves functional degeneration and nutrient redistribution. NAM/ATAF1/CUC (NAC) transcription factors orchestrate various senescence-related signals and mediate the fine-tuning underlying plant senescence. Previous data revealed that knockout of either NtNAC028 or NtNAC080 leads to delayed leaf senescence in tobacco (Nicotiana tabacum), which implies that NtNAC028 and NtNAC080 play respective roles in the regulation of leaf senescence, although they share 91.87% identity with each other. However, the mechanism underlying NtNAC028- and NtNAC080-regulated leaf senescence remains obscure. Here, we determined that NtNAC028 and NtNAC080 activate a putative jasmonic acid (JA) biosynthetic gene, NtLOX3, and enhance the JA level in vivo. We found that NtNAC028 and NtNAC080 interact with each other and themselves through their NA-terminal region. Remarkably, only the dimerization between NtNAC028 and NtNAC080 stimulated the transcriptional activation activity, but not the DNA binding activity of this heterodimer on NtLOX3. Metabolome analysis indicated that overexpression of either NtNAC028 or NtNAC080 augments both biosynthesis and degradation of nicotine in the senescent stages. Thus, we conclude that NtNAC028 cooperates with NtNAC080 and forms a heterodimer to enhance NtLOX3 expression and JA biosynthesis to trigger the onset of leaf senescence and impact secondary metabolism in tobacco.

ALLENE OXIDE SYNTHASE (AOS) induces petal senescence through a novel JA-associated regulatory pathway in Arabidopsis

Flowers are crucial for the reproduction of flowering plants and their senescence has drastic effects on plant-animal interactions as well as pollination. Petal senescence is the final phase of flower development which is regulated by hormones and genes. Among these, jasmonic acid (JA) has emerged as a major contributor to petal senescence, but its molecular mechanisms remain elusive. Here, the role of JA in petal senescence in Arabidopsis was investigated. We showed that petal senescence in aos mutant was significantly delayed, which also affected petal cell size and proliferation. Similar significant delays in petal senescence were observed in dad1 and coi1 mutants. However, MYB21/24 and MYC2/3/4, known downstream regulators of JA in flower development, played no role in petal senescence. This indicated that JA regulates petal senescence by modulating other unknown transcription factors. Transcriptomic analysis revealed that AOS altered the expression of 3681 genes associated, and identified groups of differentially expressed transcription factors, highlighting the potential involvement of AP-2, WRKY and NAC. Furthermore, bHLH13, bHLH17 and URH2 were identified as potential new regulators of JA-mediated petal senescence. In conclusion, our findings suggest a novel genetic pathway through which JA regulates petal senescence in Arabidopsis. This pathway operates independently of stamen development and leaf senescence, suggesting the evolution of specialized mechanisms for petal senescence.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12298-024-01425-w.

Lack of the CCT domain changes the ability of mango MiCOL14A to resist salt and drought stress in Arabidopsis

CONSTANS (CO) is the key gene in the photoperiodic pathway that regulates flowering in plants. In this paper, a CONSTANS-like 14A (COL14A) gene was obtained from mango, and its expression patterns and functions were characterized. Sequence analysis shows that MiCOL14A-JH has an additional A base, which leads to code shifting in subsequent coding boxes and loss of the CCT domain. The MiCOL14A-JH and MiCOL14A-GQ genes both belonged to group Ⅲ of the CO/COL gene family. Analysis of tissue expression patterns showed that MiCOL14A was expressed in all tissues, with the highest expression in the leaves of seedling, followed by lower expression levels in the flowers and stems of adult leaves. However, there was no significant difference between different mango varieties. At different development stages of flowering, the expression level of MiCOL14A-GQ was the highest in the leaves before floral induction period, and the lowest at flowering stage, while the highest expression level of MiCOL14A-JH appeared in the leaves at flowering stage. The transgenic functional analysis showed that both MiCOL14A-GQ and MiCOL14A-JH induced delayed flowering of transgenic Arabidopsis. In addition, MiCOL14A-JH enhanced the resistance of transgenic Arabidopsis to drought stress, while MiCOL14A-GQ increased the sensitivity of transgenic Arabidopsis to salt stress. Further proteinprotein interaction analysis showed that MiCOL14A-JH directly interacted with MYB30-INTERACTING E3 LIGASE 1 (MiMIEL1), CBL-interacting protein kinase 9 (MiCIPK9) and zinc-finger protein 4 (MiZFP4), but MiCOL14A-GQ could not interact with these three stress-related proteins. Together, our results demonstrated that MiCOL14A-JH and MiCOL14A-GQ not only regulate flowering but also play a role in the abiotic stress response in mango, and the lack of the CCT domain affects the proteinprotein interaction, thus affecting the gene response to stress. The insertion of an A base can provide a possible detection site for mango resistance breeding.

The CALCINEURIN B-LIKE 4/CBL-INTERACTING PROTEIN 3 module degrades repressor JAZ5 during rose petal senescence

Flower senescence is genetically regulated and developmentally controlled. The phytohormone ethylene induces flower senescence in rose (Rosa hybrida), but the underlying signaling network is not well understood. Given that calcium regulates senescence in animals and plants, we explored the role of calcium in petal senescence. Here, we report that the expression of calcineurin B-like protein 4 (RhCBL4), which encodes a calcium receptor, is induced by senescence and ethylene signaling in rose petals. RhCBL4 interacts with CBL-interacting protein kinase 3 (RhCIPK3), and both positively regulate petal senescence. Furthermore, we determined that RhCIPK3 interacts with the jasmonic acid response repressor jasmonate ZIM-domain 5 (RhJAZ5). RhCIPK3 phosphorylates RhJAZ5 and promotes its degradation in the presence of ethylene. Our results reveal that the RhCBL4-RhCIPK3-RhJAZ5 module mediates ethylene-regulated petal senescence. These findings provide insights into flower senescence, which may facilitate innovations in postharvest technology for extending rose flower longevity.

CONSTANS interacts with and antagonizes ABF transcription factors during salt stress under long-day conditions

CONSTANS (CO) is a critical regulator of flowering that combines photoperiodic and circadian signals in Arabidopsis (Arabidopsis thaliana). CO is expressed in multiple tissues, including seedling roots and young leaves. However, the roles and underlying mechanisms of CO in modulating physiological processes outside of flowering remain obscure. Here, we show that the expression of CO responds to salinity treatment. CO negatively mediated salinity tolerance under long-day (LD) conditions. Seedlings from co-mutants were more tolerant to salinity stress, whereas overexpression of CO resulted in plants with reduced tolerance to salinity stress. Further genetic analyses revealed the negative involvement of GIGANTEA (GI) in salinity tolerance requires a functional CO. Mechanistic analysis demonstrated that CO physically interacts with 4 critical basic leucine zipper (bZIP) transcription factors; ABSCISIC ACID-RESPONSIVE ELEMENT BINDING FACTOR1 (ABF1), ABF2, ABF3, and ABF4. Disrupting these ABFs made plants hypersensitive to salinity stress, demonstrating that ABFs enhance salinity tolerance. Moreover, ABF mutations largely rescued the salinity-tolerant phenotype of co-mutants. CO suppresses the expression of several salinity-responsive genes and influences the transcriptional regulation function of ABF3. Collectively, our results show that the LD-induced CO works antagonistically with ABFs to modulate salinity responses, thus revealing how CO negatively regulates plant adaptation to salinity stress.

PHOSPHATE STARVATION RESPONSE1 (PHR1) interacts with JASMONATE ZIM-DOMAIN (JAZ) and MYC2 to modulate phosphate deficiency-induced jasmonate signaling in Arabidopsis

Phosphorus (P) is a macronutrient necessary for plant growth and development. Inorganic phosphate (Pi) deficiency modulates the signaling pathway of the phytohormone jasmonate in Arabidopsis thaliana, but the underlying molecular mechanism currently remains elusive. Here, we confirmed that jasmonate signaling was enhanced under low Pi conditions, and the CORONATINE INSENSITIVE1 (COI1)-mediated pathway is critical for this process. A mechanistic investigation revealed that several JASMONATE ZIM-DOMAIN (JAZ) repressors physically interacted with the Pi signaling-related core transcription factors PHOSPHATE STARVATION RESPONSE1 (PHR1), PHR1-LIKE2 (PHL2), and PHL3. Phenotypic analyses showed that PHR1 and its homologs positively regulated jasmonate-induced anthocyanin accumulation and root growth inhibition. PHR1 stimulated the expression of several jasmonate-responsive genes, whereas JAZ proteins interfered with its transcriptional function. Furthermore, PHR1 physically associated with the basic helix-loop-helix (bHLH) transcription factors MYC2, MYC3, and MYC4. Genetic analyses and biochemical assays indicated that PHR1 and MYC2 synergistically increased the transcription of downstream jasmonate-responsive genes and enhanced the responses to jasmonate. Collectively, our study reveals the crucial regulatory roles of PHR1 in modulating jasmonate responses and provides a mechanistic understanding of how PHR1 functions together with JAZ and MYC2 to maintain the appropriate level of jasmonate signaling under conditions of Pi deficiency.

Auxin contributes to jasmonate-mediated regulation of abscisic acid signaling during seed germination in Arabidopsis

Abscisic acid (ABA) represses seed germination and postgerminative growth in Arabidopsis thaliana. Auxin and jasmonic acid (JA) stimulate ABA function; however, the possible synergistic effects of auxin and JA on ABA signaling and the underlying molecular mechanisms remain elusive. Here, we show that exogenous auxin works synergistically with JA to enhance the ABA-induced delay of seed germination. Auxin biosynthesis, perception, and signaling are crucial for JA-promoted ABA responses. The auxin-dependent transcription factors AUXIN RESPONSE FACTOR10 (ARF10) and ARF16 interact with JASMONATE ZIM-DOMAIN (JAZ) repressors of JA signaling. ARF10 and ARF16 positively mediate JA-increased ABA responses, and overaccumulation of ARF16 partially restores the hyposensitive phenotype of JAZ-accumulating plants defective in JA signaling in response to combined ABA and JA treatment. Furthermore, ARF10 and ARF16 physically associate with ABSCISIC ACID INSENSITIVE5 (ABI5), a critical regulator of ABA signaling, and the ability of ARF16 to stimulate JA-mediated ABA responses is mainly dependent on ABI5. ARF10 and ARF16 activate the transcriptional function of ABI5, whereas JAZ repressors antagonize their effects. Collectively, our results demonstrate that auxin contributes to the synergetic modulation of JA on ABA signaling, and explain the mechanism by which ARF10/16 coordinate with JAZ and ABI5 to integrate the auxin, JA, and ABA signaling pathways.

Photoperiod controls plant seed size in a CONSTANS-dependent manner

Photoperiodic plants perceive changes in day length as seasonal cues to orchestrate their vegetative and reproductive growth. Although it is known that the floral transition of photoperiod-sensitive plants is tightly controlled by day length, how photoperiod affects their post-flowering development remains to be clearly defined, as do the underlying mechanisms. Here we demonstrate that photoperiod plays a prominent role in seed development. We found that long-day (LD) and short-day (SD) plants produce larger seeds under LD and SD conditions, respectively; however, seed size remains unchanged when CONSTANS (CO), the central regulatory gene of the photoperiodic response pathway, is mutated in Arabidopsis and soybean. We further found that CO directly represses the transcription of AP2 (a known regulatory gene of seed development) under LD conditions in Arabidopsis and SD conditions in soybean, thereby controlling seed size in a photoperiod-dependent manner, and that these effects are exerted through regulation of the proliferation of seed coat epidermal cells. Collectively, our findings reveal that a crucial regulatory cascade involving CO-AP2 modulates photoperiod-mediated seed development in plants and provide new insights into how plants with different photoperiod response types perceive seasonal changes that enable them to optimize their reproductive growth.