ADA2b acts to positively regulate blue light-mediated photomorphogenesis in Arabidopsis

Cryptochromes (CRYs) act as blue light photoreceptors to regulate various plant physiological processes including photomorphogenesis and repair of DNA double strand breaks (DSBs). ADA2b is a conserved transcription co-activator that is involved in multiple plant developmental processes. It is known that ADA2b interacts with CRYs to mediate blue light-promoted DSBs repair. Whether ADA2b may participate in CRYs-mediated photomorphogenesis is unknown. Here we show that ADA2b acts to inhibit hypocotyl elongation and hypocotyl cell elongation in blue light. We found that the SWIRM domain-containing C-terminus mediates the blue light-dependent interaction of ADA2b with CRYs in blue light. Moreover, ADA2b and CRYs act to co-regulate the expression of hypocotyl elongation-related genes in blue light. Based on previous studies and these results, we propose that ADA2b plays dual functions in blue light-mediated DNA damage repair and photomorphogenesis.

Disrupting FKF1 homodimerization increases FT transcript levels in the evening by enhancing CO stabilization

KEY MESSAGE

FKF1 dimerization is crucial for proper FT levels to fine-tune flowering time. Attenuating FKF1 homodimerization increased CO abundance by enhancing its COP1 binding, thereby accelerating flowering under long days. In Arabidopsis (Arabidopsis thaliana), the blue-light photoreceptor FKF1 (FLAVIN-BINDING, KELCH REPEAT, F-BOX 1) plays a key role in inducing the expression of FLOWERING LOCUS T (FT), encoding the main florigenic signal in plants, in the late afternoon under long-day conditions (LDs) by forming dimers with FT regulators. Although structural studies have unveiled a variant of FKF1 (FKF1 I160R) that disrupts homodimer formation in vitro, the mechanism by which disrupted FKF1 homodimer formation regulates flowering time remains elusive. In this study, we determined that the attenuation of FKF1 homodimer formation enhances FT expression in the evening by promoting the increased stability of CONSTANS (CO), a primary activator of FT, in the afternoon, thereby contributing to early flowering. In contrast to wild-type FKF1, introducing the FKF1 I160R variant into the fkf1 mutant led to increased FT expression under LDs. In addition, the FKF1 I160R variant exhibited diminished dimerization with FKF1, while its interaction with GIGANTEA (GI), a modulator of FKF1 function, was enhanced under LDs. Furthermore, the FKF1 I160R variant increased the level of CO in the afternoon under LDs by enhancing its binding to COP1, an E3 ubiquitin ligase responsible for CO degradation. These findings suggest that the regulation of FKF1 homodimerization and heterodimerization allows plants to finely adjust FT expression levels around dusk by modulating its interactions with GI and COP1.

[Genotype-phenotype analysis of Fabry disease caused by GLA gene variation in a pedigree]

Objective: To investigate the clinical phenotype and genetic characteristics of patients with Fabry disease caused by a GLA variant, IVS4+919G>A. Methods: It was a prospective study. Fabry disease screening was conducted among high-risk population in Ninghai from October 2021 to August 2023. Those children with decreased α-galactosidase enzyme activity<2.40 μmol/(L·h) or elavated Lyso-GL-3 level>1.10 μg/L in dried blood spot (DBS) method underwent GLA genetic testing for diagnosis confirmation. Meanwhile, family screening was carried out. A proband and his family members diagnosed with Fabry disease were research subjects. The clinical and genetic characteristics of patients with Fabry disease caused by the GLA variant (IVS4+919G>A) were analyzed. Results: The female proband aged 9.8 years with pain in both lower limbs as the initial symptom was found to have a heterozygous GLA variant IVS4+919G>A among 102 patients. In family screening, there were 4 family members (proband's father, elder sister, elder male cousin and elder female cousin) with Fabry disease and a family member (proband's fifth aunt) with a GLA variant. Among these 4 diagnosed family members, the elder male cousin of the proband, a boy aged 13.2 years had a heterozygous GLA variant, IVS4+919G>A with intermittent pain in both lower limbs as the initial symptom. The proband's father had knee joint pain. The proband's elder sister had decreased vision and his elder female cousin had no obvious symptoms. The proband's fifth aunt with a GLA variant had decreased vision. Conclusions: High-risk screening in children and family screening are helpful for early diagnosis and treatment of Fabry disease. Neuropathic pain may be a early symptom in children with Fabry disease caused by the GLA variant, IVS4+919G>A.

PIFs interact with SWI2/SNF2-related 1 complex subunit 6 to regulate H2A.Z deposition and photomorphogenesis in Arabidopsis

Light is an essential environmental signal perceived by a broad range of photoreceptors in plants. Among them, the red/far-red light receptor phytochromes function to promote photomorphogenesis, which is critical to the survival of seedlings after seeds germination. The basic-helix-loop-helix transcription factors phytochrome-interacting factors (PIFs) are the pivotal direct downstream components of phytochromes. H2A.Z is a highly conserved histone variant regulating gene transcription, and its incorporation into nucleosomes is catalyzed by SWI2/SNF2-related 1 complex, in which SWI2/SNF2-related 1 complex subunit 6 (SWC6) and actin-related protein 6 (ARP6) serve as core subunits. Here, we show that PIFs physically interact with SWC6 in vitro and in vivo, leading to the disassociation of HY5 from SWC6. SWC6 and ARP6 regulate hypocotyl elongation partly through PIFs in red light. PIFs and SWC6 coregulate the expression of auxin-responsive genes such as IAA6, IAA19, IAA20, and IAA29 and repress H2A.Z deposition at IAA6 and IAA19 in red light. Based on previous studies and our findings, we propose that PIFs inhibit photomorphogenesis, at least in part, through repression of H2A.Z deposition at auxin-responsive genes mediated by the interactions of PIFs with SWC6 and promotion of their expression in red light.

Photoexcited cryptochromes interact with ADA2b and SMC5 to promote the repair of DNA double-strand breaks in Arabidopsis

Cryptochromes (CRYs) act as blue-light photoreceptors that regulate development and circadian rhythms in plants and animals and as navigating magnetoreceptors in migratory birds. DNA double-strand breaks (DSBs) are the most serious type of DNA damage and threaten genome stability in all organisms. Although CRYs have been shown to respond to DNA damage, whether and how they participate in DSB repair is not well understood. Here we report that Arabidopsis CRYs promote the repair of DSBs through direct interactions with ADA2b and SMC5 in a blue-light-dependent manner to enhance their interaction. Mutations in CRYs and in ADA2b lead to similar enhanced DNA damage accumulation. In response to DNA damage, CRYs are localized at DSBs, and the recruitment of SMC5 to DSBs is dependent on CRYs. These results suggest that CRY-enhanced ADA2b-SMC5 interaction promotes ADA2b-mediated recruitment of SMC5 to DSBs, leading to DSB repair.

Corrigendum: Phytochromes A and B mediate light stabilization of BIN2 to regulate brassinosteroid signaling and photomorphogenesis in Arabidopsis

[This corrects the article DOI: 10.3389/fpls.2022.865019.].

Arabidopsis cryptochrome 1 undergoes COP1 and LRBs-dependent degradation in response to high blue light

Arabidopsis cryptochrome 1 (CRY1) is an important blue light photoreceptor that promotes photomorphogenesis under blue light. The blue light photoreceptors CRY2 and phototropin 1, and the red/far-red light photoreceptors phytochromes B and A undergo degradation in response to blue and red light, respectively. This study investigated whether and how CRY1 might undergo degradation in response to high-intensity blue light (HBL). We demonstrated that CRY1 is ubiquitinated and degraded through the 26S proteasome pathway in response to HBL. We found that the E3 ubiquitin ligase constitutive photomorphogenic 1 (COP1) is involved in mediating HBL-induced ubiquitination and degradation of CRY1. We also found that the E3 ubiquitin ligases LRBs physically interact with CRY1 and are also involved in mediating CRY1 ubiquitination and degradation in response to HBL. We further demonstrated that blue-light inhibitor of cryptochromes 1 interacts with CRY1 in a blue-light-dependent manner to inhibit CRY1 dimerization/oligomerization, leading to the repression of HBL-induced degradation of CRY1. Our findings indicate that the regulation of CRY1 stability in HBL is coordinated by COP1 and LRBs, which provides a mechanism by which CRY1 attenuates its own signaling and optimizes photomorphogenesis under HBL.

Phytochromes A and B Mediate Light Stabilization of BIN2 to Regulate Brassinosteroid Signaling and Photomorphogenesis in Arabidopsis

Phytochromes A and B (phyA and phyB) are the far-red and red lights photoreceptors mediating many light responses in Arabidopsis thaliana. Brassinosteroid (BR) is a pivotal phytohormone regulating a variety of plant developmental processes including photomorphogenesis. It is known that phyB interacts with BES1 to inhibit its DNA-binding activity and repress BR signaling. Here, we show that far-red and red lights modulate BR signaling through phyA and phyB regulation of the stability of BIN2, a glycogen synthase kinase 3 (GSK3)-like kinase that phosphorylates BES1/BZR1 to inhibit BR signaling. The BIN2 gain-of-function mutant bin2-1 displays an enhanced photomorphogenic phenotype in both far-red and red lights. phyA-enhanced accumulation of BIN2 promotes the phosphorylation of BES1 in far-red light. BIN2 acts genetically downstream from PHYA to regulate photomorphogenesis under far-red light. Both phyA and phyB interact directly with BIN2, which may promote the interaction of BIN2 with BES1 and induce the phosphorylation of BES1. Our results suggest that far-red and red lights inhibit BR signaling through phyA and phyB stabilization of BIN2 and promotion of BES1 phosphorylation, which defines a new layer of the regulatory mechanism that allows plants to coordinate light and BR signaling pathways to optimize photomorphogenesis.

Arabidopsis cryptochrome 1 promotes stomatal development through repression of AGB1 inhibition of SPEECHLESS DNA-binding activity

Cryptochromes are blue light photoreceptors that mediate various light responses in plants and mammals. The heterotrimeric G-protein is known to regulate various physiological processes in plants and mammals. In Arabidopsis, cryptochrome 1 (CRY1) and the G-protein β subunit AGB1 act antagonistically to regulate stomatal development. The molecular mechanism by which CRY1 and AGB1 regulate this process remains unknown. Here, we show that Arabidopsis CRY1 acts partially through AGB1, and AGB1 acts through SPEECHLESS (SPCH), a master transcription factor that drives stomatal initiation and proliferation, to regulate stomatal development. We demonstrate that AGB1 physically interacts with SPCH to block the bHLH DNA-binding domain of SPCH and inhibit its DNA-binding activity. Moreover, we demonstrate that photoexcited CRY1 represses the interaction of AGB1 with SPCH to release AGB1 inhibition of SPCH DNA-binding activity, leading to the expression of SPCH-target genes promoting stomatal development. Taken together, our results suggest that the mechanism by which CRY1 promotes stomatal development involves positive regulation of the DNA-binding activity of SPCH mediated by CRY1 inhibition of the AGB1-SPCH interaction. We propose that the antagonistic regulation of SPCH DNA-binding activity by CRY1 and AGB1 may allow plants to balance light and G-protein signaling and optimize stomatal density and pattern.

Blue light-dependent interactions of CRY1 with GID1 and DELLA proteins regulate gibberellin signaling and photomorphogenesis in Arabidopsis

Cryptochromes are blue light photoreceptors that mediate various light responses in plants and mammals. In Arabidopsis (Arabidopsis thaliana), cryptochrome 1 (CRY1) mediates blue light-induced photomorphogenesis, which is characterized by reduced hypocotyl elongation and enhanced anthocyanin production, whereas gibberellin (GA) signaling mediated by the GA receptor GA-INSENSITIVE DWARF1 (GID1) and DELLA proteins promotes hypocotyl elongation and inhibits anthocyanin accumulation. Whether CRY1 control of photomorphogenesis involves regulation of GA signaling is largely unknown. Here, we show that CRY1 signaling involves the inhibition of GA signaling through repression of GA-induced degradation of DELLA proteins. CRY1 physically interacts with DELLA proteins in a blue light-dependent manner, leading to their dissociation from SLEEPY1 (SLY1) and the inhibition of their ubiquitination. Moreover, CRY1 interacts directly with GID1 in a blue light-dependent but GA-independent manner, leading to the inhibition of the interaction between GID1 with DELLA proteins. These findings suggest that CRY1 controls photomorphogenesis through inhibition of GA-induced degradation of DELLA proteins and GA signaling, which is mediated by CRY1 inhibition of the interactions of DELLA proteins with GID1 and SCFSLY1, respectively.

Arabidopsis cryptochrome 1 controls photomorphogenesis through regulation of H2A.Z deposition

Light is a key environmental cue that fundamentally regulates plant growth and development, which is mediated by the multiple photoreceptors including the blue light (BL) photoreceptor cryptochrome 1 (CRY1). The signaling mechanism of Arabidopsis thaliana CRY1 involves direct interactions with CONSTITUTIVE PHOTOMORPHOGENIC 1 (COP1)/SUPPRESSOR OF PHYA-105 1 and stabilization of COP1 substrate ELONGATED HYPOCOTYL 5 (HY5). H2A.Z is an evolutionarily conserved histone variant, which plays a critical role in transcriptional regulation through its deposition in chromatin catalyzed by SWR1 complex. Here we show that CRY1 physically interacts with SWC6 and ARP6, the SWR1 complex core subunits that are essential for mediating H2A.Z deposition, in a BL-dependent manner, and that BL-activated CRY1 enhances the interaction of SWC6 with ARP6. Moreover, HY5 physically interacts with SWC6 and ARP6 to direct the recruitment of SWR1 complex to HY5 target loci. Based on previous studies and our findings, we propose that CRY1 promotes H2A.Z deposition to regulate HY5 target gene expression and photomorphogenesis in BL through the enhancement of both SWR1 complex activity and HY5 recruitment of SWR1 complex to HY5 target loci, which is likely mediated by interactions of CRY1 with SWC6 and ARP6, and CRY1 stabilization of HY5, respectively.

The involvement of the N-terminal PHR domain of Arabidopsis cryptochromes in mediating light signaling

Light is a key environmental cue that fundamentally regulates all aspects of plant growth and development, which is mediated by the multiple photoreceptors including the blue light photoreceptors cryptochromes (CRYs). In Arabidopsis, there are two well-characterized homologous CRYs, CRY1 and CRY2. Whereas CRYs are flavoproteins, they lack photolyase activity and are characterized by an N-terminal photolyase-homologous region (PHR) domain and a C-terminal extension domain. It has been established that the C-terminal extension domain of CRYs is involved in mediating light signaling through direct interactions with the master negative regulator of photomorphogenesis, COP1. Recent studies have revealed that the N-terminal PHR domain of CRYs is also involved in mediating light signaling. In this review, we mainly summarize and discuss the recent advances in CRYs signaling mediated by the N-terminal PHR domain, which involves the N-terminal PHR domain-mediated dimerization/oligomerization of CRYs and physical interactions with the pivotal transcription regulators in light and phytohormone signaling.

Phytochrome B interacts with SWC6 and ARP6 to regulate H2A.Z deposition and photomorphogensis in Arabidopsis

Light serves as a crucial environmental cue which modulates plant growth and development, and which is controlled by multiple photoreceptors including the primary red light photoreceptor, phytochrome B (phyB). The signaling mechanism of phyB involves direct interactions with a group of basic helix-loop-helix (bHLH) transcription factors, PHYTOCHROME-INTERACTING FACTORS (PIFs), and the negative regulators of photomorphogenesis, COP1 and SPAs. H2A.Z is an evolutionarily conserved H2A variant which plays essential roles in transcriptional regulation. The replacement of H2A with H2A.Z is catalyzed by the SWR1 complex. Here, we show that the Pfr form of phyB physically interacts with the SWR1 complex subunits SWC6 and ARP6. phyB and ARP6 co-regulate numerous genes in the same direction, some of which are associated with auxin biosynthesis and response including YUC9, which encodes a rate-limiting enzyme in the tryptophan-dependent auxin biosynthesis pathway. Moreover, phyB and HY5/HYH act to inhibit hypocotyl elongation partially through repression of auxin biosynthesis. Based on our findings and previous studies, we propose that phyB promotes H2A.Z deposition at YUC9 to inhibit its expression through direct phyB-SWC6/ARP6 interactions, leading to repression of auxin biosynthesis, and thus inhibition of hypocotyl elongation in red light.

[Measurement of corneal nerve fiber parameters in patients with Parkinson's disease]

Objective: To analyze the characteristic changes of corneal nerve fibers in patients with Parkinson's disease (PD) by corneal confocal microscopy (CCM) and investigate the association of corneal nerve fiber parameters with disease severity and motor symptoms. Methods: Forty-two patients with PD were recruited from the Department of Neurology, Henan University People's Hospital from June 2018 to October 2019. Meanwhile, 40 healthy controls who visited the hospital for physical examination at the same period were enrolled. Corneal nerve fibers in both eyes of all participants were detected by using CCM. The differences of corneal nerve fibers were comparatively analyzed between PD group and healthy controls. Associations of corneal nerve parameters with clinical characteristics such as course of disease, Hoehn and Yahr stage (H-Y stage), unified Parkinson disease rating scale (UPDRS), levodopa equivalent daily dosage (LEDD) were analyzed by using partial correlations. The receiver operating characteristic (ROC) curve was used to analyze the capability of corneal nerve fibers for distinguishing patients with PD from healthy controls. Results: Corneal nerve fiber density (CNFD) in PD group ((19±3)/mm²) was significantly decreased compared with healthy controls ((28±4)/mm²) (t=10.798, P<0.001). However, corneal nerve branch density (CNBD) was significantly increased in PD group ((25±11)/mm²) compared with healthy controls ((18±6)/mm²) (t=-3.427, P=0.001). Meanwhile, corneal nerve fiber length (CNFL) was decreased in PD group ((11.0±2.5) mm/mm²) in comparison with healthy controls ((12.5±1.6) mm/mm²) (t=3.139, P=0.002). ROC curve analysis revealed that CNFD could discriminate PD patients from healthy controls, with an area under the curve of 0.961 3 (95%CI: 92.42-99.84, P<0.000 1). CNFD was negatively correlated with H-Y stage and UPDRS-Ⅲ (r=-0.501 and -0.399, both P<0.05). CNBD was significantly negatively associated with H-Y stage, UPDRS-Ⅲ and UPDRS-Total (r=-0.622, -0.394 and -0.354, respectively, all P<0.05). CNFL was negatively correlated with H-Y stage, UPDRS-Ⅲ and UPDRS-total (r=-0.574, -0.484 and -0.422, respectively, all P<0.05). Conclusion: Small nerve fiber injuries exist in PD patients. Corneal nerve fibers negatively correlates with motor symptoms. CNFD have a good discriminative power to distinguish PD patients from healthy controls and may serve as a marker for PD.

Photoexcited Cryptochrome2 Interacts Directly with TOE1 and TOE2 in Flowering Regulation

Cryptochromes are photolyase-like, blue-light (BL) photoreceptors found in various organisms. Arabidopsis (Arabidopsis thaliana) cryptochromes (CRYs; CRY1, and CRY2) mediate many light responses including photoperiodic floral initiation. Cryptochromes interact with COP1 and SPA1, causing the stabilization of CONSTANS (CO) and promotion of FLOWERING LOCUS T (FT) transcription and flowering. The AP2-like transcriptional factor TOE1 negatively regulates FT expression and flowering by indirectly inhibiting CO transcriptional activation activity and directly binding to FT Here, we demonstrate that CRY1 and CRY2 physically interact with TOE1 and TOE2 in a BL-dependent manner in flowering regulation. Genetic studies showed that mutation of TOE1 and TOE2 partially suppresses the late-flowering phenotype of cry1 cry2 mutant plants. BL-triggered interactions of CRY2 with TOE1 and TOE2 promote the dissociation of TOE1 and TOE2 from CO, resulting in alleviation of their inhibition of CO transcriptional activity and enhanced transcription of FT Furthermore, we show that CRY2 represses TOE1 binding to the regulatory element within the Block E enhancer of FT These results reveal that TOE1 and TOE2 act as downstream components of CRY2, thus partially mediating CRY2 regulation of photoperiodic flowering through modulation of CO activity and FT transcription.

A dynamic model of UVR8 photoreceptor signalling in UV-B-acclimated Arabidopsis

The photoreceptor UVR8 mediates numerous photomorphogenic responses of plants to UV-B wavelengths by regulating transcription. Studies with purified UVR8 and seedlings not previously exposed to UV-B have generated a model for UVR8 action in which dimeric UVR8 rapidly monomerises in response to UV-B exposure to initiate signalling. However, the mechanism of UVR8 action in UV-B-acclimated plants growing under photoperiodic conditions, where UVR8 exists in a dimer/monomer photo-equilibrium, is poorly understood. We examined UVR8 dimer/monomer status, gene expression responses, amounts of key UVR8 signalling proteins and their interactions with UVR8 in UV-B-acclimated Arabidopsis. We show that in UV-B-acclimated plants UVR8 can mediate a response to a 15-fold increase in UV-B without any increase in abundance of UVR8 monomer. Following transfer to elevated UV-B, monomers show increased interaction with both COP1, to initiate signalling and RUP2, to maintain the photo-equilibrium when the dimer/monomer cycling rate increases. Native RUP1 is present in low abundance compared with RUP2. We present a model for UVR8 action in UV-B-acclimated plants growing in photoperiodic conditions that incorporates dimer and monomer photoreception, dimer/monomer cycling, abundance of native COP1 and RUP proteins, and interactions of the monomer population with COP1, RUP2 and potentially other proteins.

Corrigendum: Arabidopsis G-Protein β Subunit AGB1 Interacts With BES1 to Regulate Brassinosteroid Signaling and Cell Elongation

[This corrects the article DOI: 10.3389/fpls.2017.02225.].

[Depletion of PRDM9 inhibited the osteogenic differentiation potential of periodontal ligament stem cells]

Objective: To investigate the effect of PR domain zinc finger protein 9 (PRDM9), one of the histone methylated transferases, on osteogenic differentiation ability of periodontal ligament mesenchymal stem cells (PDLSC). Methods: PDLSC with PRDM9 gene knocked down by PRDM9 shRNA using recombinant lentiviral vector were allocated into the PRDM9sh group, and the transfected shRNA was as the control group. The gene expression efficiency was evaluated by reverse transcription polymerase chain reaction (RT-PCR). Alkaline phosphatase activity (ALP), alizarin red staining, mineralization and osteocalcin, which belongs to osteogenic differentiation markers detected by RT-PCR and Western blotting to detect the osteogenic differentiation ability of stem cells from periodontal ligaments in vitro. In vivo, PRDM9sh and control group cells was transplanted into the dorsal dermal to explore the osteogenesis. The area percentage of new osteogenic tissue was calculated by image pro software and statistically analyzed. Results: RT-PCR results showed that the relative expression of PRDM9 gene in PRDM9sh (0.460±0.017) was significantly lower than that in control group (1.000±0.107) (P<0.05). The results of ALP activity determined at 5 days postinduction in a significant decrease in PRDM9sh cells (0.762±0.063) compared with control group (1.225±0.058) (P<0.01). Alizarin red staining induced by osteogenesis at 2 weeks and 3 weeks showed that the staining of PRDM9sh was significantly lighter than that in control group. Quantitative calcium analysis results showed that the calcium ion concentration induced by osteogenesis at 2 weeks and 3 weeks [(0.071±0.004), (0.075±0.001)] in PRDM9sh was significantly lower than that in control group at 2 weeks and 3 weeks [(0.282±0.006), (0.485+0.004)] (P<0.01). RT-PCR results showed that the relative expression of osteocalcin mRNA in PRDM9sh (1.059±0.148) was significantly lower than that in control group at 2 weeks (2.542±0.190) (P<0.01). Western blotting results showed that osteocalcin expression in PRDM9sh was significantly lower than that in control group at 1 and 2 weeks after osteogenesis induction. Animal transplantation experiments results indicated that PRDM9 significantly inhibited the osteogenesis of PDLSC in vivo, and the proportion of osteogenic area calculated showed that the osteogenic capacity of PRDM9sh [(3.8±2.41)%] was significantly lower than that in control group [(24.54±7.06)%](P<0.05). Conclusions: Depletion of PRDM9 repressed the osteogenic differentiation of stem cells from periodontal ligament in vitro and in vivo.

Photoexcited CRY1 and phyB interact directly with ARF6 and ARF8 to regulate their DNA-binding activity and auxin-induced hypocotyl elongation in Arabidopsis

Arabidopsis CRY1 and phyB are the primary blue and red light photoreceptors mediating blue and red light inhibition of hypocotyl elongation, respectively. Auxin is a pivotal phytohormone involved in promoting hypocotyl elongation. CRY1 and phyB interact with and stabilize auxin/indole acetic acid proteins (Aux/IAAs) to inhibit auxin signaling. The present study investigated whether photoreceptors might interact directly with Auxin Response Factors (ARFs) to regulate auxin signaling. Protein-protein interaction studies demonstrated that CRY1 and phyB interact physically with ARF6 and ARF8 through their N-terminal domains in a blue and red light-dependent manner, respectively. Moreover, the N-terminal DNA-binding domain of ARF6 and ARF8 is involved in mediating their interactions with CRY1. Genetic studies showed that ARF6 and ARF8 act partially downstream from CRY1 and PHYB to regulate hypocotyl elongation under blue and red light, respectively. Chromatin immunoprecipitation-PCR assays demonstrated that CRY1 and phyB mediate blue and red light repression of the DNA-binding activity of ARF6 and ARF6-target gene expression, respectively. Altogether, the results herein suggest that the direct repression of auxin-responsive gene expression mediated by the interactions of CRY1 and phyB with ARFs constitutes a new layer of the regulatory mechanisms by which light inhibits auxin-induced hypocotyl elongation.

[Retrospective analysis of 13 cases of nocardiosis]

Objective: To evaluate the clinical features, chest radiological manifestations, microbiological examination and treatments of nocardial disease. Methods: A retrospective study was conducted to analyze the data of patients with nocardial infection admitted to Beijing Chaoyang Hospital from January 2010 to January 2016. Results: The 13 patients, 6 males and 7 females, aged (51±17) years. Twelve cases were diagnosed with pulmonary nocardiosis, and 1 with disseminated nocardial infection. Most of these patients had complications: autoimmune diseases in 3 (2 with autoimmune hemolytic anemia and 1 with systemic lupus erythematosus), and bronchiectasis in 6 patients. The most common symptoms were cough, expectoration and fever. The main manifestations of CT scans included nodules or masses, bronchiectasis, ground glass opacity, cavity and pleural thickening. Six cases were confirmed by sputum smear microscopy, 4 by bronchoalveolar lavage, 2 by percutaneous lung biopsy and 1 by renal abscess puncture. After diagnosis, antibiotics such as Co-trimoxazole, amikacin, cephalosporins, imipenem, minomycin, or linezolid were used, and the 13 patients were all cured and discharged. Conclusions: Pulmonary nocardiosis was the most common clinical presentation of nocardial infection. Cough, expectoration and fever were the most common symptoms. The main findings of CT scans were nodules or masses, bronchiectasis, ground glass opacity, cavity and pleural thickening. The diagnosis of nocardiosis was not easy because of the non-specific clinical presentations and difficult culture of nocardia spp. Thus, high clinical suspicion of nocardiosis is necessary for earlier diagnosis and treatment.

Phytochrome B and AGB1 Coordinately Regulate Photomorphogenesis by Antagonistically Modulating PIF3 Stability in Arabidopsis

Phytochrome B (phyB), the primary red light photoreceptor, promotes photomorphogenesis in Arabidopsis by interacting with the basic helix-loop-helix transcriptional factor PIF3 and inducing its phosphorylation and degradation. Heterotrimeric G proteins are known to regulate various developmental processes in plants and animals. In Arabidopsis, the G-protein β subunit AGB1 is known to repress photomorphogenesis. However, whether and how phyB and AGB1 coordinately regulate photomorphogenesis are largely unknown. Here we show that phyB physically interacts with AGB1 in a red light-dependent manner and that AGB1 interacts directly with PIF3. Moreover, we demonstrate that the AGB1-PIF3 interaction inhibits the association of PIF3 with phyB, leading to reduced phosphorylation and degradation of PIF3, whereas the phyB-AGB1 interaction represses the association of PIF3 with AGB1, resulting in enhanced phosphorylation and degradation of PIF3. Our results suggest that phyB and AGB1 antagonistically regulate PIF3 stability by dynamically interacting with each other and PIF3. This dynamic mechanism may allow plants to balance phyB and G-protein signaling to optimize photomorphogenesis.

Photoexcited CRYPTOCHROME 1 Interacts Directly with G-Protein β Subunit AGB1 to Regulate the DNA-Binding Activity of HY5 and Photomorphogenesis in Arabidopsis

Light and the heterotrimeric G-protein are known to antagonistically regulate photomorphogenesis in Arabidopsis. However, whether light and G-protein coordinate the regulation of photomorphogenesis is largely unknown. Here we show that the blue light photoreceptor cryptochrome 1 (CRY1) physically interacts with the G-protein β subunit, AGB1, in a blue light-dependent manner. We also show that AGB1 directly interacts with HY5, a basic leucine zipper transcriptional factor that acts as a critical positive regulator of photomorphogenesis, to inhibit its DNA-binding activity. Genetic studies suggest that CRY1 acts partially through AGB1, and AGB1 acts partially through HY5 to regulate photomorphogenesis. Moreover, we demonstrate that blue light-triggered interaction of CRY1 with AGB1 promotes the dissociation of HY5 from AGB1. Our results suggest that the CRY1 signaling mechanism involves positive regulation of the DNA-binding activity of HY5 mediated by the CRY1-AGB1 interaction, which inhibits the association of AGB1 with HY5. We propose that the antagonistic regulation of HY5 DNA-binding activity by CRY1 and AGB1 may allow plants to balance light and G-protein signaling and optimize photomorphogenesis.

[Correlation between ultrasonographic optic nerve sheath diameter and intracranial pressure]

Objective: To evaluate the association of the ultrasonographic optic nerve sheath diameter (ONSD) and intracranial pressure (ICP), and the feasibility of ultrasonographic ONSD in predicting high ICP. Methods: A prospective study. The outpatients who planned to measure ICP by lumbar puncture in Department of Neurology, Xuanwu Hospital, Capital Medical University were selected from January 2011 to May 2012. All the retrobulbar ONSD measurement with B-scan ultrasound was performed just before lumbar puncture. When high ICP was defined as ICP more than 200 mmH₂O(1 mmH₂O=0.009 8 kPa), the participants were divided into the high ICP group and the normal ICP group. The Pearson correlation coefficient analysis was used to analyze the correlation between ICP and postbulbar ONSD measurements. The difference in ONSD was compared between the high ICP and normal ICP groups with the t test. The receiver operating characteristic (ROC) curve was used to calculate the cutoff value of mean ONSD and evaluate the sensitivity and specificity of the method. Results: A total of 130 participants were involved in this study. There were 71 males and 59 females, aged (38±14) years.The mean ICP was (209.84±79.99) mmH₂O. The mean ONSD was (5.68±0.78) mm in the right eyes, (5.78±0.78) mm in the left eyes, and (5.73±0.71) mm in both eyes. The ICP had a significant correlation with ONSD in the right eyes (r=0.54, P<0.001), ONSD in the left eyes (r=0.56, P<0.001) and ONSD in both eyes (r=0.60, P<0.001), but no correlation with age (r=-0.14, P=0.114) and gender (r=0.20, P=0.817). The ONSD in the high ICP group (n=65) was (6.11±0.66) mm, (6.22±0.56) mm and (6.17±0.50) mm in the right eyes, left eyes, and both eyes, respectively. Compared with the ONSD in the normal ICP group (n=65), which was (5.26±0.64) mm in the right eyes, (5.34±0.72) mm in the left eyes and (5.30±0.62) mm in both eyes, there was a significantly enlarged ONSD in the high ICP group (t=-7.507, -7.778, -8.779, all P<0.001). The ROC analysis showed the ONSD of 5.6 mm was the best cutoff value with a sensitivity of 86% and a specificity of 71% for identifying high ICP. Conclusions: There is a significantly positive correlation between ICP and postbulbar ONSD measured by ultrasound. This non-invasive method may be an alternative approach to predicting the ICP value of patients whose ICP measurement via lumbar puncture is at high risk. However, it can not replace the direct ICP measurement with the invasive method. (Chin J Ophthalmol, 2018, 54: 683-687).

Photoexcited CRYPTOCHROME1 Interacts with Dephosphorylated BES1 to Regulate Brassinosteroid Signaling and Photomorphogenesis in Arabidopsis

Cryptochromes (CRYs) are blue light photoreceptors that mediate a variety of light responses in plants and animals, including photomorphogenesis, flowering, and circadian rhythms. The signaling mechanism by which Arabidopsis thaliana cryptochromes CRY1 and CRY2 promote photomorphogenesis involves direct interactions with COP1, a RING motif-containing E3 ubiquitin ligase, and its enhancer SPA1. Brassinosteroid (BR) is a key phytohormone involved in the repression of photomorphogenesis, and here, we show that the signaling mechanism of Arabidopsis CRY1 involves the inhibition of BR signaling. CRY1 and CRY2 physically interact with BES1-INTERACTING MYC-LIKE1 (BIM1), a basic helix-loop-helix protein. BIM1, in turn, interacts with and enhances the activity of BRI1-EMS SUPPRESSOR1 (BES1), a master transcription factor in the BR signaling pathway. In addition, CRY1 and CRY2 interact specifically with dephosphorylated BES1, the physiologically active form of BES1 that is activated by BR in a blue light-dependent manner. The CRY1-BES1 interaction leads to both the inhibition of BES1 DNA binding activity and the repression of its target gene expression. Our study suggests that the blue light-dependent, BR-induced interaction of CRY1 with BES1 is a tightly regulated mechanism by which plants optimize photomorphogenesis according to the availability of external light and internal BR signals.

Photoactivated CRY1 and phyB Interact Directly with AUX/IAA Proteins to Inhibit Auxin Signaling in Arabidopsis

Light is a key environmental cue that inhibits hypocotyl cell elongation through the blue and red/far-red light photoreceptors cryptochrome- and phytochrome-mediated pathways in Arabidopsis. In contrast, as a pivotal endogenous phytohormone auxin promotes hypocotyl elongation through the auxin receptors TIR1/AFBs-mediated degradation of AUX/IAA proteins (AUX/IAAs). However, the molecular mechanisms underlying the antagonistic interaction of light and auxin signaling remain unclear. Here, we report that light inhibits auxin signaling through stabilization of AUX/IAAs by blue and red light-dependent interactions of cryptochrome 1 (CRY1) and phytochrome B with AUX/IAAs, respectively. Blue light-triggered interactions of CRY1 with AUX/IAAs inhibit the associations of TIR1 with AUX/IAAs, leading to the repression of auxin-induced degradation of these proteins. Our results indicate that photoreceptors share AUX/IAAs with auxin receptors as the same direct downstream signaling components. We propose that antagonistic regulation of AUX/IAA protein stability by photoreceptors and auxin receptors allows plants to balance light and auxin signals to optimize their growth.

Arabidopsis G-Protein β Subunit AGB1 Interacts with BES1 to Regulate Brassinosteroid Signaling and Cell Elongation

In Arabidopsis, brassinosteroids (BR) are major growth-promoting hormones, which integrate with the heterotrimeric guanine nucleotide-binding protein (G-protein) signals and cooperatively modulate cell division and elongation. However, the mechanisms of interaction between BR and G-protein are not well understood. Here, we show that the G-protein β subunit AGB1 directly interacts with the BR transcription factor BES1 in vitro and in vivo. An AGB1-null mutant, agb1-2, displays BR hyposensitivity and brassinazole (BRZ, BR biosynthesis inhibitor) hypersensitivity, which suggests that AGB1 positively mediates the BR signaling pathway. Moreover, we demonstrate that AGB1 synergistically regulates expression of BES1 target genes, including the BR biosynthesis genes CPD and DWF4 and the SAUR family genes required for promoting cell elongation. Further, Western blot analysis of BES1 phosphorylation states indicates that the interaction between AGB1 and BES1 alters the phosphorylation status of BES1 and increases the ratio of dephosphorylated to phosphorylated BES1, which leads to accumulation of dephosphorylated BES1 in the nucleus. Finally, AGB1 promotes BES1 binding to BR target genes and stimulates the transcriptional activity of BES1. Taken together, our results demonstrate that AGB1 positively regulates cell elongation by affecting the phosphorylation status and transcriptional activity of BES1.

DELLA proteins physically interact with CONSTANS to regulate flowering under long days in Arabidopsis

Proper timing of flowering is essential for reproduction of plants. Although it is well known that both light and gibberellin (GA) signaling play critical roles in promoting flowering in Arabidopsis thaliana, whether and how they are integrated to regulate flowering remain largely unknown. Here, we show through biochemical studies that DELLA proteins physically interact with CONSTANS (CO). Furthermore, the interaction of CO with NF-YB2 is inhibited by the DELLA protein, RGA. Our findings suggest that regulation of flowering by GA signaling in leaves under long days is mediated, at least in part, through repression of DELLA proteins on CO, providing a molecular link between DELLA proteins, key components in GA signaling pathway, and CO, a critical flowering activator in photoperiod signaling pathway.

Transcriptome Analyses Reveal the Involvement of Both C and N Termini of Cryptochrome 1 in Its Regulation of Phytohormone-Responsive Gene Expression in Arabidopsis

Cryptochromes (CRY) are blue-light photoreceptors that mediate various light responses in plants and animals. It has long been demonstrated that Arabidopsis CRY (CRY1 and CRY2) C termini (CCT1 and CCT2) mediate light signaling through direct interaction with COP1. Most recently, CRY1 N terminus (CNT1) has been found to be involved in CRY1 signaling independent of CCT1, and implicated in the inhibition of gibberellin acids (GA)/brassinosteroids (BR)/auxin-responsive gene expression. Here, we performed RNA-Seq assay using transgenic plants expressing CCT1 fused to β-glucuronidase (GUS-CCT1, abbreviated as CCT1), which exhibit a constitutively photomorphogenic phenotype, and compared the results with those obtained previously from cry1cry2 mutant and the transgenic plants expressing CNT1 fused to nuclear localization signal sequence (NLS)-tagged YFP (CNT1-NLS-YFP, abbreviated as CNT1), which display enhanced responsiveness to blue light. We found that 2903 (67.85%) of the CRY-regulated genes are regulated by CCT1 and that 1095 of these CCT1-regulated genes are also regulated by CNT1. After annotating the gene functions, we found that CCT1 is involved in mediating CRY1 regulation of phytohormone-responsive genes, like CNT1, and that about half of the up-regulated genes by GA/BR/auxin are down-regulated by CCT1 and CNT1, consistent with the antagonistic role for CRY1 and these phytohormones in regulating hypocotyl elongation. Physiological studies showed that both CCT1 and CNT1 are likely involved in mediating CRY1 reduction of seedlings sensitivity to GA under blue light. Furthermore, protein expression studies demonstrate that the inhibition of GA promotion of HY5 degradation by CRY1 is likely mediated by CCT1, but not by CNT1. These results give genome-wide transcriptome information concerning the signaling mechanism of CRY1, unraveling possible involvement of its C and N termini in its regulation of response of GA and likely other phytohormones.

Brief reports: TRPM7 Senses mechanical stimulation inducing osteogenesis in human bone marrow mesenchymal stem cells

Mesenchymal stem cells (MSCs) are multipotential stem cells residing in the bone marrow. Several studies have shown that mechanical stimulation modulates MSC differentiation through mobilization of second messengers, but the mechanism of mechanotransduction remains poorly understood. In this study, using fluorescence and laser confocal microcopy as well as patch-clamp techniques, we identified the transient receptor potential melastatin type 7 (TRPM7) channel as the key channel involved in mechanotransduction in bone marrow MSCs. TRPM7 knockdown completely abolished the pressure-induced cytosolic Ca(2+) increase and pressure-induced osteogenesis. TRPM7 directly sensed membrane tension, independent of the cytoplasm and the integrity of cytoskeleton. Ca(2+) influx through TRPM7 further triggered Ca(2+) release from the inositol trisphosphate receptor type 2 on the endoplasmic reticulum and promoted NFATc1 nuclear localization and osteogenesis. These results identified a central role of TRPM7 in MSC mechanical stimulation-induced osteogenesis.

Red-light-dependent interaction of phyB with SPA1 promotes COP1-SPA1 dissociation and photomorphogenic development in Arabidopsis

Arabidopsis phytochromes (phyA-phyE) are photoreceptors dedicated to sensing red/far-red light. Phytochromes promote photomorphogenic developments upon light irradiation via a signaling pathway that involves rapid degradation of PIFs (PHYTOCHROME INTERACTING FACTORS) and suppression of COP1 (CONSTITUTIVE PHOTOMORPHOGENIC 1) nuclear accumulation, through physical interactions with PIFs and COP1, respectively. Both phyA and phyB, the two best characterized phytochromes, regulate plant photomorphogenesis predominantly under far-red light and red light, respectively. It has been demonstrated that SPA1 (SUPPRESSOR OF PHYTOCHROME A 1) associates with COP1 to promote COP1 activity and suppress photomorphogenesis. Here, we report that the mechanism underlying phyB-promoted photomorphogenesis in red light involves direct physical and functional interactions between red-light-activated phyB and SPA1. We found that SPA1 acts genetically downstream of PHYB to repress photomorphogenesis in red light. Protein interaction studies in both yeast and Arabidopsis demonstrated that the photoactivated phyB represses the association of SPA1 with COP1, which is mediated, at least in part, through red-light-dependent interaction of phyB with SPA1. Moreover, we show that phyA physically interacts with SPA1 in a Pfr-form-dependent manner, and that SPA1 acts downstream of PHYA to regulate photomorphogenesis in far-red light. This study provides a genetic and biochemical model of how photoactivated phyB represses the activity of COP1-SPA1 complex through direct interaction with SPA1 to promote photomorphogenesis in red light.

Housefly maggot-treated composting as sustainable option for pig manure management

In traditional composting, large amounts of bulking agents must be added to reduce the moisture of pig manure, which increases the cost of composting and dilutes the N, P and K content in organic fertilizers. In this study, maggot treatment was used in composting instead of bulking agents. In experiment of selecting an optimal inoculum level for composting, the treatment of 0.5% maggot inoculum resulted in the maximum yield of late instar maggots, 11.6% (maggots weight/manure weight). The manure residue became noticeably granular by day 6 and its moisture content was below 60%, which was suitable for further composting without bulking agents. Moreover, in composting experiment with a natural compost without maggot inoculum and maggot-treated compost at 0.5% inoculum level, there were no significant differences in nutrient content between the two organic fertilizers from the two treatments (paired Student's t15=1.0032, P=0.3317). Therefore, maggot culturing did not affect the characteristics of the organic fertilizer. The content of TNPK (total nitrogen+total phosphorus+total potassium) in organic fertilizer from maggot treatment was 10.72% (dry weight), which was far more than that of organic fertilizer made by conventional composting with bulking agents (about 8.0%). Dried maggots as feed meet the national standard (GB/T19164-2003) for commercial fish meal in China, which contained 55.32 ± 1.09% protein; 1.34 ± 0.02% methionine; 4.15 ± 0.10% lysine. This study highlights housefly maggot-treated composting can be considered sustainable alternatives for pig manure management to achieve high-quality organic fertilizer and maggots as feed without bulking agents.

Jasmonic acid enhancement of anthocyanin accumulation is dependent on phytochrome A signaling pathway under far-red light in Arabidopsis

Anthocyanins are critical for plants. It is shown that the expression of genes encoding the key enzymes such as dihydroflavonol 4-reductase (DFR), UDP-Glc: flavonoid 3-O-glucosyltransferase (UF3GT), and leucoanthocyanidin dioxygenase (LDOX) in anthocyanin biosynthesis pathway is regulated by MYB75, a R2R3 MYB transcription factor. The production of anthocyanin is known to be promoted by jasmonic acid (JA) in light but not in darkness. The photoreceptors cryptochrome 1 (CRY1), phytochrome B (phyB), and phytochrome A (phyA) are also shown to mediate light promotion of anthocyanin accumulation, respectively, whereas their downstream factor COP1, a master negative regulator of photomorphogensis, represses anthocyanin accumulation. However, whether JA coordinates with photoreceptors in the regulation of anthocyanin accumulation is unknown. Here, we show that under far-red light, JA promotes anthocyanin accumulation in a phyA signaling pathway-dependent manner. The phyA mutant is hyposensitive to jasmonic acid analog methyl jasmonic acid (MeJA) under far-red light. The dominant mutant of MYB75, pap1-D, accumulates significantly higher levels of anthocyanin than wild type under far-red light, whereas knockdown of MYBs (MYB75, MYB90, MYB113, and MYB114) through RNAi significantly reduces MeJA promotion of anthocyanin accumulation. The phyA pap1-D double mutant shows reduced responsiveness to MeJA, similar to phyA mutant under far-red light. In darkness, a mutant allele of cop1, cop1-4, shows enhanced responsiveness to MeJA, but pap1-D mutant is barely responsive to MeJA. Upon MeJA application, the cop1-4 pap1-D double mutant accumulates considerably higher levels of anthocyanin than cop1-4 in darkness. Protein studies indicate that MYB75 protein is stabilized by white light and far-red light. Further gene expression studies suggest that MeJA promotes the expression of DFR, UF3GT, and LDOX genes in a phyA- and MYB75-dependent manner under far-red light. Our findings suggest that JA promotion of anthocyanin accumulation under far-red light is dependent on phyA signaling pathway, consisting of phyA, COP1, and MYB75.

Molecular cloning, sequence analysis, prokaryotic expression, and function prediction of foot-specific peroxidase in Hydra magnipapillata Chinese strain

The cDNA sequence of foot-specific peroxidase PPOD1 from the Chinese strain of Hydra magnipapillata was cloned by reverse transcription-polymerase chain reaction. The cDNA sequence contained a coding region with an 873-bp open reading frame, a 31-bp 5'-untranslated region, and a 36-bp 3'-untranslated region. The structure prediction results showed that PPOD1 contains 10.34% of α-helix, 38.62% of extended strand, 12.41% of β-turn, and 38.62% of random coil. The structural core was α-helix at the N terminus. The GenBank protein blast server showed that PPOD1 contains 2 fascin-like domains. In addition, high-level PPOD1 activity was only present in the ectodermal epithelial cells located on the edge of the adhesive face of the basal disc, and that these cells extended lamellipodia and filopodia when the basal disc was tightly attached to a glass slide. The fascin-like domains of Hydra PPOD1 might contribute to the bundling of the actin filament of these cells, and hence, the formation of filopodia. In conclusion, these cells might play an important role in strengthening the adsorbability of the basal disc to substrates.

COP1 and phyB Physically Interact with PIL1 to Regulate Its Stability and Photomorphogenic Development in Arabidopsis

In Arabidopsis thaliana, the cryptochrome and phytochrome photoreceptors act together to promote photomorphogenic development. The cryptochrome and phytochrome signaling mechanisms interact directly with CONSTITUTIVELY PHOTOMORPHOGENIC1 (COP1), a RING motif-containing E3 ligase that acts to negatively regulate photomorphogenesis. COP1 interacts with and ubiquitinates the transcription factors that promote photomorphogenesis, such as ELONGATED HYPOCOTYL5 and LONG HYPOCOTYL IN FAR-RED1 (HFR1), to inhibit photomorphogenic development. Here, we show that COP1 physically interacts with PIF3-LIKE1 (PIL1) and promotes PIL1 degradation via the 26S proteasome. We further demonstrate that phyB physically interacts with PIL1 and enhances PIL1 protein accumulation upon red light irradiation, probably through suppressing the COP1-PIL1 association. Biochemical and genetic studies indicate that PIL1 and HFR1 form heterodimers and promote photomorphogenesis cooperatively. Moreover, we demonstrate that PIL1 interacts with PIF1, 3, 4, and 5, resulting in the inhibition of the transcription of PIF direct-target genes. Our results reveal that PIL1 stability is regulated by phyB and COP1, likely through physical interactions, and that PIL1 coordinates with HFR1 to inhibit the transcriptional activity of PIFs, suggesting that PIL1, HFR1, and PIFs constitute a subset of antagonistic basic helix-loop-helix factors acting downstream of phyB and COP1 to regulate photomorphogenic development.

Strigolactone-regulated hypocotyl elongation is dependent on cryptochrome and phytochrome signaling pathways in Arabidopsis

Seedling development including hypocotyl elongation is a critical phase in the plant life cycle. Light regulation of hypocotyl elongation is primarily mediated through the blue light photoreceptor cryptochrome and red/far-red light photoreceptor phytochrome signaling pathways, comprising regulators including COP1, HY5, and phytochrome-interacting factors (PIFs). The novel phytohormones, strigolactones, also participate in regulating hypocotyl growth. However, how strigolactone coordinates with light and photoreceptors in the regulation of hypocotyl elongation is largely unclear. Here, we demonstrate that strigolactone inhibition of hypocotyl elongation is dependent on cryptochrome and phytochrome signaling pathways. The photoreceptor mutants cry1 cry2, phyA, and phyB are hyposensitive to strigolactone analog GR24 under the respective monochromatic light conditions, while cop1 and pif1 pif3 pif4 pif5 (pifq) quadruple mutants are hypersensitive to GR24 in darkness. Genetic studies indicate that the enhanced responsiveness of cop1 to GR24 is dependent on HY5 and MAX2, while that of pifq is independent of HY5. Further studies demonstrate that GR24 constitutively up-regulates HY5 expression in the dark and light, whereas GR24-promoted HY5 protein accumulation is light- and cryptochrome and phytochrome photoreceptor-dependent. These results suggest that the light dependency of strigolactone regulation of hypocotyl elongation is likely mediated through MAX2-dependent promotion of HY5 expression, light-dependent accumulation of HY5, and PIF-regulated components.

Auxin controls seed dormancy through stimulation of abscisic acid signaling by inducing ARF-mediated ABI3 activation in Arabidopsis

The transition from dormancy to germination in seeds is a key physiological process during the lifecycle of plants. Abscisic acid (ABA) is the sole plant hormone known to maintain seed dormancy; it acts through a gene expression network involving the transcription factor ABSCISIC ACID INSENSITIVE 3 (ABI3). However, whether other phytohormone pathways function in the maintenance of seed dormancy in response to environmental and internal signals remains an important question. Here, we show that the plant growth hormone auxin, which acts as a versatile trigger in many developmental processes, also plays a critical role in seed dormancy in Arabidopsis. We show that disruptions in auxin signaling in MIR160-overexpressing plants, auxin receptor mutants, or auxin biosynthesis mutants dramatically release seed dormancy, whereas increases in auxin signaling or biosynthesis greatly enhance seed dormancy. Auxin action in seed dormancy requires the ABA signaling pathway (and vice versa), indicating that the roles of auxin and ABA in seed dormancy are interdependent. Furthermore, we show that auxin acts upstream of the major regulator of seed dormancy, ABI3, by recruiting the auxin response factors AUXIN RESPONSE FACTOR 10 and AUXIN RESPONSE FACTOR 16 to control the expression of ABI3 during seed germination. Our study, thus, uncovers a previously unrecognized regulatory factor of seed dormancy and a coordinating network of auxin and ABA signaling in this important process.

Substitution of a conserved glycine in the PHR domain of Arabidopsis cryptochrome 1 confers a constitutive light response

CRYPTOCHROMES (CRYs) are photolyase-like ultraviolet-A/blue light photoreceptors that mediate various light responses in plants. The signaling mechanism of Arabidopsis CRYs (CRY1 and CRY2) involves direct CRY-COP1 interaction. Here, we report that CRY1(G380R), which carries a Gly-to-Arg substitution of the highly conserved G380 in the photolyase-related (PHR) domain of Arabidopsis CRY1, shows constitutive CRY1 photoreceptor activity in Arabidopsis. Transgenic plants overexpressing CRY1(G380R) display a constitutively photomorphogenic (COP) phenotype in darkness, as well as a dramatic early flowering phenotype under short-day light conditions (SD). We further demonstrate that CRY1(G380R) expression driven by the native CRY1 promoter also results in a COP phenotype in darkness. Moreover, overexpression of either the Arabidopsis homolog CRY2(G377R) or the rice ortholog OsCRY1b(G388R) of CRY1(G380R) in Arabidopsis results in a COP phenotype in darkness. Cellular localization studies indicate that CRY1(G380R) co-localizes with COP1 in the same nuclear bodies (NBs) in vivo and inhibits the nuclear accumulation of COP1 in darkness. These results suggest that the conserved G380 may play a critical role in regulating the photoreceptor activity of plant CRYs and that CRY1(G380R) might constitutively phenocopy the photo-activated CRY1 in darkness and thus constitutively mediate CRY1 signaling.

A gain-of-function mutation in IAA7/AXR2 confers late flowering under short-day light in Arabidopsis

Floral initiation is a major step in the life cycle of plants, which is influenced by photoperiod, temperature, and phytohormones, such as gibberellins (GAs). It is known that GAs promote floral initiation under short-day light conditions (SDs) by regulating the floral meristem-identity gene LEAFY (LFY) and the flowering-time gene SUPPRESSOR OF OVEREXPRESSION OF CO 1 (SOC1). We have defined the role of the auxin signaling component INDOLE-3-ACETIC ACID 7 (IAA7)/AUXIN RESISTANT 2 (AXR2) in the regulation of flowering time in Arabidopsis thaliana. We demonstrate that the gain-of-function mutant of IAA7/AXR2, axr2-1, flowers late under SDs. The exogenous application of GAs rescued the late flowering phenotype of axr2-1 plants. The expression of the GA20 oxidase (GA20ox) genes, GA20ox1 and GA20ox2, was reduced in axr2-1 plants, and the levels of both LFY and SOC1 transcripts were reduced in axr2-1 mutants under SDs. Furthermore, the overexpression of SOC1 or LFY in axr2-1 mutants rescued the late flowering phenotype under SDs. Our results suggest that IAA7/AXR2 might act to inhibit the timing of floral transition under SDs, at least in part, by negatively regulating the expressions of the GA20ox1 and GA20ox2 genes.

Blue-light-dependent interaction of cryptochrome 1 with SPA1 defines a dynamic signaling mechanism

Cryptochromes (CRYs) are blue-light photoreceptors that mediate various light responses in plants and animals. The signaling mechanism by which CRYs regulate light responses involves their physical interactions with COP1. Here, we report that CRY1 interacts physically with SPA1 in a blue-light-dependent manner. SPA acts genetically downstream from CRYs to regulate light-controlled development. Blue-light activation of CRY1 attenuates the association of COP1 with SPA1 in both yeast and plant cells. These results indicate that the blue-light-triggered CRY1-SPA1 interaction may negatively regulate COP1, at least in part, by promoting the dissociation of COP1 from SPA1. This interaction and consequent dissociation define a dynamic photosensory signaling mechanism.

MicroRNA171c-targeted SCL6-II, SCL6-III, and SCL6-IV genes regulate shoot branching in Arabidopsis

MicroRNAs (miRNAs) are ∼21-nucleotide noncoding RNAs that play critical roles in regulating plant growth and development through directing the degradation of target mRNAs. Axillary meristem activity, and hence shoot branching, is influenced by a complicated network that involves phytohormones such as auxin, cytokinin, and strigolactone. GAI, RGA, and SCR (GRAS) family members take part in a variety of developmental processes, including axillary bud growth. Here, we show that the Arabidopsis thaliana microRNA171c (miR171c) acts to negatively regulate shoot branching through targeting GRAS gene family members SCARECROW-LIKE6-II (SCL6-II), SCL6-III, and SCL6-IV for cleavage. Transgenic plants overexpressing MIR171c (35Spro-MIR171c) and scl6-II scl6-III scl6-IV triple mutant plants exhibit a similar reduced shoot branching phenotype. Expression of any one of the miR171c-resistant versions of SCL6-II, SCL6-III, and SCL6-IV in 35Spro-MIR171c plants rescues the reduced shoot branching phenotype. Scl6-II scl6-III scl6-IV mutant plants exhibit pleiotropic phenotypes such as increased chlorophyll accumulation, decreased primary root elongation, and abnormal leaf and flower patterning. SCL6-II, SCL6-III, and SCL6-IV are located to the nucleus, and show transcriptional activation activity. Our results suggest that miR171c-targeted SCL6-II, SCL6-III, and SCL6-IV play an important role in the regulation of shoot branch production.

CRYPTOCHROME 1 is implicated in promoting R protein-mediated plant resistance to Pseudomonas syringae in Arabidopsis

Plants have evolved complex mechanisms to defend themselves against pathogens. It has been shown that several defense responses are influenced by light, and the red/far-red light photoreceptor phytochromes (PHY) modulate plant defense responses in Arabidopsis. Blue light receptor cryptochromes (CRY) work together with PHY to regulate many light-controlled responses, including photomorphogenesis, floral induction, and entrainment of the circadian clock. We report here that the Arabidopsis blue light photoreceptor CRY1 positively regulates inducible resistance to Pseudomonas syringae under continuous light conditions. By challenging plants with P. syringae pv. tomato (Pst.) DC3000 carrying avrRpt2, we demonstrate that effector-triggered local resistance is down-regulated in the cry1 mutant, leading to more pathogen multiplication. In plants overexpressing CRY1 (CRY1-ovx), however, local resistance is significantly up-regulated. We also show that systemic acquired resistance (SAR) is positively regulated by CRY1, and that salicylic acid (SA)-induced pathogenesis-related gene PR-1 expression is reduced in the cry1 mutant, but enhanced in CRY1-ovx plants. However, our results indicate that CRY1 only modestly influences SA accumulation and has no effect on hypersensitive cell death. These results suggest that CRY1 may positively regulate R protein-mediated resistance to P. syringae with increased PR gene expression.

Phytochrome B is involved in mediating red light-induced stomatal opening in Arabidopsis thaliana

The stomatal pores of higher plants enable gaseous exchange into and out of leaves for photosynthesis and evaporation. Stomatal opening is induced by both blue and red lights. It is shown that blue light-induced stomatal opening is mediated by the blue light receptor phototropins (PHOT1 and PHOT2) and cryptochromes (CRY1 and CRY2). However, whether phytochrome B (phyB) is involved in red light regulation of stomatal opening remains largely unclear. Here, we report a positive role for Arabidopsis (Arabidopsis thaliana) phyB in the regulation of red light-induced stomatal opening. The phyB mutant stomata displayed a reduced red light response, whereas stomata of the phyB-overexpressing plants displayed a hypersensitive response to red light. In addition, stomata of the cry1 cry2 phyB, phot1 phot2 phyB, and cry1 phyA phyB triple mutant plants showed more reduced light response than those of the single or double mutant plants under white light, implying that phyB acts in concert with phyA, CRY, and PHOT in light regulation of stomatal opening. Stomata of phyB cop1 mutant opened less wide than those of the cop1 mutant, and stomata of the pif3 pif4 mutant opened wider than those of the wild-type, indicating that COP1, together with the PIFs (phytochrome interacting factors), may act downstream of PHYB in regulating stomatal opening. Furthermore, quantitative RT-PCR analysis showed that the expression of MYB60 was reduced in the cry1 cry2 and phyA phyB mutants under blue and red lights, respectively, but induced in the CRY1- and phyB-overexpressing plants. These results demonstrate that phyB and CRY might regulate stomatal opening, at least in part, by regulating MYB60 expression.

Cryptochromes, phytochromes, and COP1 regulate light-controlled stomatal development in Arabidopsis

In Arabidopsis thaliana, the cryptochrome (CRY) blue light photoreceptors and the phytochrome (phy) red/far-red light photoreceptors mediate a variety of light responses. COP1, a RING motif-containing E3 ubiquitin ligase, acts as a key repressor of photomorphogenesis. Production of stomata, which mediate gas and water vapor exchange between plants and their environment, is regulated by light and involves phyB and COP1. Here, we show that, in the loss-of-function mutants of CRY and phyB, stomatal development is inhibited under blue and red light, respectively. In the loss-of-function mutant of phyA, stomata are barely developed under far-red light. Strikingly, in the loss-of-function mutant of either COP1 or YDA, a mitogen-activated protein kinase kinase kinase, mature stomata are developed constitutively and produced in clusters in both light and darkness. CRY, phyA, and phyB act additively to promote stomatal development. COP1 acts genetically downstream of CRY, phyA, and phyB and in parallel with the leucine-rich repeat receptor-like protein TOO MANY MOUTHS but upstream of YDA and the three basic helix-loop-helix proteins SPEECHLESS, MUTE, and FAMA, respectively. These findings suggest that light-controlled stomatal development is likely mediated through a crosstalk between the cryptochrome-phytochrome-COP1 signaling system and the mitogen-activated protein kinase signaling pathway.

COP1-mediated ubiquitination of CONSTANS is implicated in cryptochrome regulation of flowering in Arabidopsis

In Arabidopsis thaliana, the blue light photoreceptor cryptochromes (CRY) act to promote photomorphogenic development and the transition from vegetative to floral development in long days (LDs). We previously proposed that one of the mechanisms by which CRY regulates light responses is via its physical interaction with COP1, a RING motif-containing E3 ligase. Under LDs, the transcription of FLOWERING LOCUS T (FT) is activated by CONSTANS (CO) in leaf, and the FT protein moves to the shoot apex to induce flowering. CO protein is degraded in darkness, whereas it is stabilized by the CRY-mediated signal. However, the mechanism underlying this process is unknown. We show in this report that CO acts genetically downstream of COP1 and CRY to regulate flowering time. In addition, COP1 physically interacts with CO and functions as an E3 ligase, ubiquitinating CO in vitro and reducing CO levels in vivo. These results suggest that COP1 acts as a repressor of flowering by promoting the ubiquitin-mediated proteolysis of CO in darkness and that CRY-mediated signal may negatively regulate COP1, thereby stabilizing CO, activating FT transcription, and inducing flowering.

Cryptochrome signaling in plants

Cryptochromes are blue light receptors that mediate various light-induced responses in plants and animals. They share sequence similarity to photolyases, flavoproteins that catalyze the repair of UV light-damaged DNA, but do not have photolyase activity. Arabidopsis cryptochromes work together with the red/far-red light receptor phytochromes to regulate various light responses, including the regulation of cell elongation and photoperiodic flowering, and are also found to act together with the blue light receptor phototropins to mediate blue light regulation of stomatal opening. The signaling mechanism of Arabidopsis cryptochromes is mediated through negative regulation of COP1 by direct CRY-COP1 interaction through CRY C-terminal domain. Arabidopsis CRY dimerized through its N-terminal domain and dimerization of CRY is required for light activation of the photoreceptor activity. Recently, significant progresses have been made in our understanding of cryptochrome functions in other dicots such as pea and tomato and lower plants including moss and fern. This review will focus on recent advances in functional and mechanism characterization of cryptochromes in plants. It is not intended to cover every aspect of the field; readers are referred to other review articles for historical perspectives and a more comprehensive understanding of this photoreceptor.

Functional and signaling mechanism analysis of rice CRYPTOCHROME 1

Cryptochromes (CRY) are blue-light photoreceptors that mediate various light responses, such as inhibition of hypocotyl elongation, enhancement of cotyledon expansion, anthocyanin accumulation and stomatal opening in Arabidopsis. The signaling mechanism of Arabidopsis CRY is mediated through direct interaction with COP1, a negative regulator of photomorphogenesis. CRY has now been characterized in tomato, pea, moss and fern, but its function in monocots is largely unknown. Here we report the function and basic signaling mechanism of rice cryptochrome 1 (OsCRY1). Overexpresion of OsCRY1b resulted in a blue light-dependent short hypcotyl phenotype in Arabidopsis, and a short coleoptile, leaf sheath and leaf blade phenotype in rice (Oryza sativa). On fusion with beta-glucuronidase (GUS), the C-terminal domain of either OsCRY1a (OsCCT1a) or OsCRY1b (OsCCT1b) mediated a constitutive photomorphogenic (COP) phenotype in both Arabidopsis and rice, whereas OsCCT1b mutants corresponding to missense mutations in previously described Arabidopsis cry1 alleles failed to confer a COP phenotype. Yeast two-hybrid and subcellular co-localization studies demonstrated that OsCRY1b interacted physically with rice COP1 (OsCOP1). From these results, we conclude that OsCRY1 is implicated in blue-light inhibition of coleoptile and leaf elongation during early seedling development in rice, and that the signaling mechanism of OsCRY1 involves direct interaction with OsCOP1.