Gibberellin acts through jasmonate to control the expression of MYB21, MYB24, and MYB57 to promote stamen filament growth in Arabidopsis.
ABSTRACT: Precise coordination between stamen and pistil development is essential to make a fertile flower. Mutations impairing stamen filament elongation, pollen maturation, or anther dehiscence will cause male sterility. Deficiency in plant hormone gibberellin (GA) causes male sterility due to accumulation of DELLA proteins, and GA triggers DELLA degradation to promote stamen development. Deficiency in plant hormone jasmonate (JA) also causes male sterility. However, little is known about the relationship between GA and JA in controlling stamen development. Here, we show that MYB21, MYB24, and MYB57 are GA-dependent stamen-enriched genes. Loss-of-function of two DELLAs RGA and RGL2 restores the expression of these three MYB genes together with restoration of stamen filament growth in GA-deficient plants. Genetic analysis showed that the myb21-t1 myb24-t1 myb57-t1 triple mutant confers a short stamen phenotype leading to male sterility. Further genetic and molecular studies demonstrate that GA suppresses DELLAs to mobilize the expression of the key JA biosynthesis gene DAD1, and this is consistent with the observation that the JA content in the young flower buds of the GA-deficient quadruple mutant ga1-3 gai-t6 rga-t2 rgl1-1 is much lower than that in the WT. We conclude that GA promotes JA biosynthesis to control the expression of MYB21, MYB24, and MYB57. Therefore, we have established a hierarchical relationship between GA and JA in that modulation of JA pathway by GA is one of the prerequisites for GA to regulate the normal stamen development in Arabidopsis.
Project description: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.
Project description:The phytohormone jasmonates (JAs) regulate various defense responses and diverse developmental processes including stamen development and fertility. Previous studies showed that JA induces CORONATINE INSENSITIVE 1-mediated degradation of JA ZIM-domain (JAZ) proteins, and activates the MYB transcription factors (such as MYB21 and MYB24) to regulate stamen development. In this study, we further uncover the mechanism underlying how MYB24 interacts with JAZs to control JA-regulated stamen development. We show that N-terminus of MYB21/24 interacts with 10 out of 12 JAZ proteins while both N-terminus and C-terminus of MYB24 are involved in dimerization of MYB21 and MYB24. Interestingly, male sterility of the JA-deficient mutant opr3 can be rescued by suitable level of the MYB24 overexpression but not by excessive high level of MYB24. Surprisingly, overexpression of MYB24NT, but not MYB24CT, could cause male sterility. These results provide new insights on MYB factors in JA-regulated stamen development.
Project description:The function of the plant hormone jasmonic acid (JA) in development of tomato flowers was analyzed with a mutant defective in JA perception (jasmonate-insensitive1-1, jai1-1). In contrast to Arabidopsis JA-insensitive plants that are male sterile, the tomato mutant jai1-1 exhibits major defects in female development resulting in female sterility. To identify putative JA-dependent regulatory components, transcriptomics was performed using isolated ovules of three different stages of flower development, from both wild type and jai1-1. Among the strongly down-regulated genes in jai1-1, one encoding a MYB transcription factor (SlMYB21) was found. Its orthologue in Arabidopsis has a crucial role in JA-regulated stamen development. SlMYB21 showed transcription factor activity in yeast, interaction with SlJAZ9 in yeast and in planta, and complemented the Arabidopsis mutant myb21-5. To analyze SlMYB21 function in tomato ovule development, CRISPR/Cas9 mutants were created and a TILLING mutant was identified, all showing female sterility and therefore corroborating a function of MYB21 in tomato ovule development. Transcriptomics from wild type, jai1-1 and myb21-2 carpels revealed processes that might be controlled by SlMYB21. The data suggest a positive regulation of JA biosynthesis by SlMYB21, but a negative regulation of the action of auxin and GA. The results demonstrate that SlMYB21 mediates at least partially the action of JA and might control the flower to fruit transition.
Project description:The DELLA family of transcription regulators functions as master growth repressors in plants by inhibiting phytohormone gibberellin (GA) signaling in response to developmental and environmental cues. DELLAs also play a central role in mediating cross-talk between GA and other signaling pathways via antagonistic direct interactions with key transcription factors. However, how these crucial protein-protein interactions can be dynamically regulated during plant development remains unclear. Here, we show that DELLAs are modified by the O-linked N-acetylglucosamine (O-GlcNAc) transferase (OGT) SECRET AGENT (SEC) in Arabidopsis. O-GlcNAcylation of the DELLA protein REPRESSOR OF ga1-3 (RGA) inhibits RGA binding to four of its interactors-PHYTOCHROME-INTERACTING FACTOR3 (PIF3), PIF4, JASMONATE-ZIM DOMAIN1, and BRASSINAZOLE-RESISTANT1 (BZR1)-that are key regulators in light, jasmonate, and brassinosteroid signaling pathways, respectively. Consistent with this, the sec-null mutant displayed reduced responses to GA and brassinosteroid and showed decreased expression of several common target genes of DELLAs, BZR1, and PIFs. Our results reveal a direct role of OGT in repressing DELLA activity and indicate that O-GlcNAcylation of DELLAs provides a fine-tuning mechanism in coordinating multiple signaling activities during plant development.
Project description:Gibberellins (GAs) are a class of plant hormones involved in the regulation of flower development in Arabidopsis. The GA-deficient ga1-3 mutant shows retarded growth of all floral organs, especially abortive stamen development that results in complete male sterility. Until now, it has not been clear how GA regulates the late-stage development of floral organs after the establishment of their identities within floral meristems. Various combinations of null mutations of DELLA proteins can gradually rescue floral defects in ga1-3. In particular, the synergistic effect of rga-t2 and rgl2-1 can substantially restore flower development in ga1-3. We find that the transcript levels of floral homeotic genes APETALA3 (AP3), PISTILLATA (PI), and AGAMOUS (AG) are immediately upregulated in young flowers of ga1-3 upon GA treatment. Using a steroid-inducible activation of RGA, we further demonstrated that these floral homeotic genes are transcriptionally repressed by RGA activity in young flowers whereas the expression of LEAFY (LFY) and APETALA1 (AP1) is not substantially affected. In addition, we observed the partial rescue of floral defects in ga1-3 by overexpression of AG. Our results indicate that GA promotes the expression of floral homeotic genes by antagonizing the effects of DELLA proteins, thereby allowing continued flower development.
Project description:Gibberellins (GAs) are a class of important phytohormones regulating a variety of physiological processes during normal plant growth and development. One of the major events during GA-mediated growth is the degradation of DELLA proteins, key negative regulators of GA signaling pathway. The stability of DELLA proteins is thought to be controlled by protein phosphorylation and dephosphorylation. Up to date, no phosphatase involved in this process has been identified. We have identified a dwarfed dominant-negative Arabidopsis mutant, named topp4-1. Reduced expression of TOPP4 using an artificial microRNA strategy also resulted in a dwarfed phenotype. Genetic and biochemical analyses indicated that TOPP4 regulates GA signal transduction mainly via promoting DELLA protein degradation. The severely dwarfed topp4-1 phenotypes were partially rescued by the DELLA deficient mutants rga-t2 and gai-t6, suggesting that the DELLA proteins RGA and GAI are required for the biological function of TOPP4. Both RGA and GAI were greatly accumulated in topp4-1 but significantly decreased in 35S-TOPP4 transgenic plants compared to wild-type plants. Further analyses demonstrated that TOPP4 is able to directly bind and dephosphorylate RGA and GAI, confirming that the TOPP4-controlled phosphorylation status of DELLAs is associated with their stability. These studies provide direct evidence for a crucial role of protein dephosphorylation mediated by TOPP4 in the GA signaling pathway.
Project description:For self-pollinating plants to reproduce, male and female organ development must be coordinated as flowers mature. The Arabidopsis transcription factors AUXIN RESPONSE FACTOR 6 (ARF6) and ARF8 regulate this complex process by promoting petal expansion, stamen filament elongation, anther dehiscence, and gynoecium maturation, thereby ensuring that pollen released from the anthers is deposited on the stigma of a receptive gynoecium. ARF6 and ARF8 induce jasmonate production, which in turn triggers expression of MYB21 and MYB24, encoding R2R3 MYB transcription factors that promote petal and stamen growth. To understand the dynamics of this flower maturation regulatory network, we have characterized morphological, chemical, and global gene expression phenotypes of arf, myb, and jasmonate pathway mutant flowers. We found that MYB21 and MYB24 promoted not only petal and stamen development but also gynoecium growth. As well as regulating reproductive competence, both the ARF and MYB factors promoted nectary development or function and volatile sesquiterpene production, which may attract insect pollinators and/or repel pathogens. Mutants lacking jasmonate synthesis or response had decreased MYB21 expression and stamen and petal growth at the stage when flowers normally open, but had increased MYB21 expression in petals of older flowers, resulting in renewed and persistent petal expansion at later stages. Both auxin response and jasmonate synthesis promoted positive feedbacks that may ensure rapid petal and stamen growth as flowers open. MYB21 also fed back negatively on expression of jasmonate biosynthesis pathway genes to decrease flower jasmonate level, which correlated with termination of growth after flowers have opened. These dynamic feedbacks may promote timely, coordinated, and transient growth of flower organs.
Project description:The C-repeat binding factor (CBF) is crucial for regulation of cold response in higher plants. In Arabidopsis, the mechanism of CBF3-caused growth retardation is still unclear. Our present work shows that CBF3 shares the similar repression of bioactive gibberellin (GA) as well as upregulation of DELLA proteins with CBF1 and -2. Genetic analysis reveals that DELLAs play an essential role in growth reduction mediated by CBF1, -2, -3 genes. The in vivo and in vitro evidences demonstrate that GA2-oxidase 7 gene is a novel CBF3 regulon. Meanwhile, DELLAs contribute to cold induction of CBF1, -2, -3 genes through interaction with jasmonate (JA) signaling. We conclude that CBF3 promotes DELLAs accumulation through repressing GA biosynthesis and DELLAs positively regulate CBF3 involving JA signaling. CBFs and DELLAs collaborate to retard plant growth in response to low temperature.
Project description:Flower maturation consists of several events that contribute to reproductive success as flowers open, including petal expansion, stamen filament elongation, pollen release, nectary maturation, stigma growth, and gynoecium maturation to support pollen tube growth. The Arabidopsis transcription factors ARF6 (Auxin Response Factor 6) and ARF8 regulate all of these processes, in part by activating jasmonate biosynthesis. Jasmonates in turn activate genes encoding the transcription factors MYB21 and MYB24, which mediate a subset of the processes controlled by ARF6 and ARF8. This experiment was designed to characterize gene expression in flowers before and after they open, and to determine how arf6 arf8 and myb21 myb24 mutation combinations affect these gene expression patterns. Three biological replicates were prepared at each of two developmental stages, stage 12 (oldest closed buds) and stage 13 (youngest open flowers), for three genotypes (Wild type, arf6-2 arf8-3, and myb21-5 myb24-5). For the mutant genotypes, stage 13 flowers do not actually open, so corresponding flowers of equivalent age were chosen based on the position of open flowers in wild-type inflorescences.
Project description:Gibberellins (GAs) play a critical role in fruit-set and fruit growth. Gibberellin is perceived by its nuclear receptors GA INSENSITIVE DWARF1s (GID1s), which then trigger degradation of downstream repressors DELLAs. To understand the role of the three GA receptor genes (GID1A, GID1B and GID1C) in Arabidopsis during fruit initiation, we have examined their temporal and spatial localization, in combination with analysis of mutant phenotypes. Distinct expression patterns are revealed for each GID1: GID1A is expressed throughout the whole pistil, while GID1B is expressed in ovules, and GID1C is expressed in valves. Functional study of gid1 mutant combinations confirms that GID1A plays a major role during fruit-set and growth, whereas GID1B and GID1C have specific roles in seed development and pod elongation, respectively. Therefore, in ovules, GA perception is mediated by GID1A and GID1B, while GID1A and GID1C are involved in GA perception in valves. To identify tissue-specific interactions between GID1s and DELLAs, we analyzed spatial expression patterns of four DELLA genes that have a role in fruit initiation (GAI, RGA, RGL1 and RGL2). Our data suggest that GID1A can interact with RGA and GAI in all tissues, whereas GID1C-RGL1 and GID1B-RGL2 interactions only occur in valves and ovules, respectively. These results uncover specific functions of each GID1-DELLA in the different GA-dependent processes that occur upon fruit-set. In addition, the distribution of GA receptors in valves along with lack of expression of GA biosynthesis genes in this tissue, strongly suggests transport of GAs from the developing seeds to promote fruit growth.