Alternative localization of HEME OXYGENASE 1 in plant cells regulates cytosolic heme catabolism.

Heme, an organometallic tetrapyrrole, is widely engaged in oxygen transport, electron delivery, enzymatic reactions, and signal transduction. In plants, it is also involved in photomorphogenesis and photosynthesis. HEME OXYGENASE 1 (HO1) initiates the first committed step in heme catabolism, and it has generally been thought that this reaction takes place in chloroplasts. Here, we show that HO1 in both Arabidopsis (Arabidopsis thaliana) and rice (Oryza sativa) has two transcription start sites (TSSs), producing long (HO1L) and short (HO1S) transcripts. Their products localize to the chloroplast and the cytosol, respectively. During early development or de-etiolation, the HO1L/HO1S ratio gradually increases. Light perception via phytochromes and cryptochromes elevates the HO1L/HO1S ratio in the whole seedling through the functions of ELONGATED HYPOCOTYL 5 (HY5) and HY5 HOMOLOG (HYH) and through the suppression of DE-ETIOLATED 1 (DET1), CONSTITUTIVE PHOTOMORPHOGENESIS 1 (COP1), and PHYTOCHROME INTERACTING FACTORs (PIFs). HO1L introduction complements the HO1-deficient mutant; surprisingly, HO1S expression also restores the short hypocotyl phenotype and high pigment content and helps the mutant recover from the genomes uncoupled (gun) phenotype. This indicates the assembly of functional phytochromes within these lines. Furthermore, our findings support the hypothesis that a mobile heme signal is involved in retrograde signaling from the chloroplast. Altogether, our work clarifies the molecular mechanism of HO1 TSS regulation and highlights the presence of a cytosolic bypass for heme catabolism in plant cells.

The Arabidopsis katamari2 Mutant Exhibits a Hypersensitive Seedling Arrest Response at the Phase Transition from Heterotrophic to Autotrophic Growth.

Young seedlings use nutrients stored in the seeds to grow and acquire photosynthetic potential. This process, called seedling establishment, involves a developmental phase transition from heterotrophic to autotrophic growth. Some membrane-trafficking mutants of Arabidopsis (Arabidopsis thaliana), such as the katamari2 (kam2) mutant, exhibit growth arrest during seedling development, with a portion of individuals failing to develop true leaves on sucrose-free solid medium. However, the reason for this seedling arrest is unclear. In this study, we show that seedling arrest is a temporal growth arrest response that occurs not only in kam2 but also in wild-type (WT) Arabidopsis; however, the threshold for this response is lower in kam2 than in the WT. A subset of the arrested kam2 seedlings resumed growth after transfer to fresh sucrose-free medium. Growth arrest in kam2 on sucrose-free medium was restored by increasing the gel concentration of the medium or covering the surface of the medium with a perforated plastic sheet. WT Arabidopsis seedlings were also arrested when the gel concentration of sucrose-free medium was reduced. RNA sequencing revealed that transcriptomic changes associated with the rate of seedling establishment were observed as early as 4 d after sowing. Our results suggest that the growth arrest of both kam2 and WT seedlings is an adaptive stress response and is not simply caused by the lack of a carbon source in the medium. This study provides a new perspective on an environmental stress response under unfavorable conditions during the phase transition from heterotrophic to autotrophic growth in Arabidopsis.

Stomatal regulators are co-opted for seta development in the astomatous liverwort Marchantia polymorpha.

The evolution of special types of cells requires the acquisition of new gene regulatory networks controlled by transcription factors (TFs). In stomatous plants, a TF module formed by subfamilies Ia and IIIb basic helix-loop-helix TFs (Ia-IIIb bHLH) regulates stomatal formation; however, how this module evolved during land plant diversification remains unclear. Here we show that, in the astomatous liverwort Marchantia polymorpha, a Ia-IIIb bHLH module regulates the development of a unique sporophyte tissue, the seta, which is found in mosses and liverworts. The sole Ia bHLH gene, MpSETA, and a IIIb bHLH gene, MpICE2, regulate the cell division and/or differentiation of seta lineage cells. MpSETA can partially replace the stomatal function of Ia bHLH TFs in Arabidopsis thaliana, suggesting that a common regulatory mechanism underlies setal and stomatal formation. Our findings reveal the co-option of a Ia-IIIb bHLH TF module for regulating cell fate determination and/or cell division of distinct types of cells during land plant evolution.

Cryptochromes suppress leaf senescence in response to blue light in Arabidopsis.

The induction and progression of leaf senescence are effectively changed according to the light environment. The leaf senescence response is enhanced when plants are grown under a dense shade cast by neighboring vegetation. Although the fluence rate of the red and blue regions in the light spectrum is strongly attenuated under shade, photosensory mechanisms that underpin the blue light response are still unclear. In this study, we analyzed leaf senescence in response to blue light in Arabidopsis (Arabidopsis thaliana). We found that leaf senescence was promoted by the elimination of active phytochrome Pfr by pulsed far-red (FR) light, whereas irradiation with blue light suppressed leaf senescence in the wild type but not in the cryptochrome (CRY)-deficient mutant, cry1 cry2. Hence, two light-sensing modes contributed to the suppression of leaf senescence that was dependent on light spectrum features. First was the leaf senescence response to blue light, which was mediated exclusively by cryptochromes. Second was the phytochrome-mediated leaf senescence response to red/FR light. Physiological analysis of transgenic plants expressing green fluorescent protein (GFP)-tagged CRY2 revealed that photo-activation of cryptochromes was required to suppress leaf senescence in response to blue light. Transcriptomic analysis further uncovered the molecular and cellular processes involved in the regulation of leaf senescence downstream of cryptochromes. Furthermore, analysis of cryptochrome-downstream components indicated that ELONGATED HYPOCOTYL 5 (HY5) and PHYTOCHROME INTERACTING FACTOR (PIF) 4 and PIF5 were required for suppression and promotion of leaf senescence, respectively.

Comprehensive analysis of peptide-coding genes and initial characterization of an LRR-only microprotein in Marchantia polymorpha.

In the past two decades, many plant peptides have been found to play crucial roles in various biological events by mediating cell-to-cell communications. However, a large number of small open reading frames (sORFs) or short genes capable of encoding peptides remain uncharacterized. In this study, we examined several candidate genes for peptides conserved between two model plants: Arabidopsis thaliana and Marchantia polymorpha. We examined their expression pattern in M. polymorpha and subcellular localization using a transient assay with Nicotiana benthamiana. We found that one candidate, MpSGF10B, was expressed in meristems, gemma cups, and male reproductive organs called antheridiophores. MpSGF10B has an N-terminal signal peptide followed by two leucine-rich repeat (LRR) domains and was secreted to the extracellular region in N. benthamiana and M. polymorpha. Compared with the wild type, two independent Mpsgf10b mutants had a slightly increased number of antheridiophores. It was revealed in gene ontology enrichment analysis that MpSGF10B was significantly co-expressed with genes related to cell cycle and development. These results suggest that MpSGF10B may be involved in the reproductive development of M. polymorpha. Our research should shed light on the unknown role of LRR-only proteins in land plants.

Case Report: Lifesaving Hemostasis With Resuscitative Endovascular Balloon Occlusion of the Aorta in a Patient With Cardiac Arrest Caused by Upper Gastrointestinal Hemorrhage.

Resuscitative endovascular balloon occlusion of the aorta (REBOA) is performed to treat hemorrhagic shock, whose cause is located below the diaphragm. However, its use in patients with gastrointestinal hemorrhage is relatively rare. The 45-year-old man with a history of dilated cardiomyopathy had experienced epigastric discomfort and had an episode of presyncope. On his presentation, the patient's blood pressure was 82/64 mmHg, heart rate 140/min, and consciousness level GCS E4V5M6. Hemodynamics stabilized rapidly with a transfusion that was administered on an emergency basis, and a blood sample only showed mild anemia (Hb, 11.5 g/dL). The patient was admitted to investigating the presyncope episode, and the planned endoscopy was scheduled the following day. The patient had an episode of presyncope soon and was found in hemorrhagic shock resulting from a duodenal ulcer rapidly deteriorated to cardiac arrest. Although a spontaneous heartbeat was restored with cardiopulmonary resuscitation, the patient's hemodynamics were unstable despite the emergency blood transfusion administered by pumping. Consequently, a REBOA device was placed, resuscitation was continued, and hemostasis was achieved by vascular embolization for the gastroduodenal artery. The patient was subsequently discharged without complications. However, there is no established evidence regarding the REBOA use in upper gastrointestinal hemorrhage, and the investigations that have been reported have been limited. Further, one recent research suggests that appropriate patient selection and early use may improve survival in these life-threatening cases. As was seen in the present case, REBOA can effectively treat upper gastrointestinal hemorrhage by temporarily stabilizing hemodynamics and enabling a hemostatic procedure to be quickly performed during that time. This report also demonstrated the hemodynamics during the combination of intermittent and partial REBOA to avoid the complications of ischemic or reperfusion injury of the intestines or lower extremities.

Divergence in red light responses associated with thermal reversion of phytochrome B between high- and low-latitude species.

Phytochromes play a central role in mediating adaptive responses to light and temperature throughout plant life cycles. Despite evidence for adaptive importance of natural variation in phytochromes, little information is known about molecular mechanisms that modulate physiological responses of phytochromes in nature. We show evolutionary divergence in physiological responses relevant to thermal stability of a physiologically active form of phytochrome (Pfr) between two sister species of Brassicaceae growing at different latitudes. The higher latitude species (Cardamine bellidifolia; Cb) responded more strongly to light-limited conditions compared with its lower latitude sister (C. nipponica; Cn). Moreover, CbPHYB conferred stronger responses to both light-limited and warm conditions in the phyB-deficient mutant of Arabidopsis thaliana than CnPHYB: that is Pfr CbphyB was more stable in nuclei than CnphyB. Our findings suggest that fine tuning Pfr stability is a fundamental mechanism for plants to optimise phytochrome-related traits in their evolution and adapt to spatially varying environments, and open a new avenue to understand molecular mechanisms that fine tune phytochrome responses in nature.

Simultaneous brain and lung metastases of pancreatic ductal adenocarcinoma after curative pancreatectomy: a case report and literature review.

BACKGROUND: Pancreatic ductal adenocarcinoma (PDAC) rarely metastasizes to the brain; therefore, the features of brain metastasis of PDAC are still unknown. We encountered simultaneous metastases to the brain and lung in a PDAC patient after curative surgery. Case presentation A 68-year-old man with PDAC in the tail of the pancreas underwent distal pancreato-splenectomy. He received gemcitabine as adjuvant chemotherapy for 6 months. Two months later, brain and lung metastases occurred simultaneously. Considering the systemic condition, the patient received gamma knife treatment and an Ommaya reservoir was inserted for drainage. The patient's condition gradually worsened and he received the best supportive care. To the best of our knowledge, only 28 cases in which brain metastases of PDAC were identified at the time of ante-mortem have been reported to date, including the present case. Notably, the percentage of simultaneous brain and lung metastases was higher (32%) in a series of reviewed cohorts. Thus, lung metastasis might be one of the risk factors for the development of brain metastasis in patients with PDAC. As a systemic disease, it can be inferred that neoplastic cells will develop brain metastasis via hematogenous dissemination beyond the blood-brain barrier, even if local recurrence is controlled. In our case, immunohistochemical staining showed that the neoplastic cells were positive for carbonic anhydrase 9 (CAIX), mucin core protein 1 (MUC1), and MUC5AC in the resected primary PDAC. CONCLUSION: We describe a case of simultaneous brain and lung metastases of PDAC after curative pancreatectomy, review previous literature, and discuss the clinical features of brain metastasis of PDAC.

[A Case Report of R0 Resection after Chemotherapy for Locally Advanced Pancreatic Head Cancer with Ureter Invasion].

A 60-year-old woman was referred to our hospital due to pancreatic head cancer with right ureter invasion. We considered that it was difficult to achieve R0 resection for the patient by operation because of a wide range of retroperitoneal invasions involving the right ureter. She was treated with chemotherapy(gemcitabine plus nab-paclitaxel: GnP). GnP therapy was administered 3-weeks on/1-week off for 1 course. After 3 courses, we performed pancreaticoduodenectomy, right nephrectomy and partial transverse colectomy. We achieved R0 resection and considered the GnP therapy to be effective.

Light Activates Brassinosteroid Biosynthesis to Promote Hook Opening and Petiole Development in Arabidopsis thaliana.

Although brassinosteroids (BRs) have been proposed to be negative regulators of photomorphogenesis, their physiological role therein has remained elusive. We studied light-induced photomorphogenic development in the presence of the BR biosynthesis inhibitor, brassinazole (Brz). Hook opening was inhibited in the presence of Brz; this inhibition was reversed in the presence of brassinolide (BL). Hook opening was accompanied by cell expansion on the inner (concave) side of the hook. This cell expansion was inhibited in the presence of Brz but was restored upon the addition of BL. We then evaluated light-induced organ-specific expression of three BR biosynthesis genes, DWF4, BR6ox1 and BR6ox2, and a BR-responsive gene, SAUR-AC1, during the photomorphogenesis of Arabidopsis. Expression of these genes was induced, particularly in the hook region, in response to illumination. The induction peaked after 3 h of light exposure and preceded hook opening. Phytochrome-deficient mutants, hy1, hy2 and phyAphyB, and a light-signaling mutant, hy5, were defective in light-induced expression of BR6ox1, BR6ox2 and SAUR-AC1. Light induced both expression of BR6ox genes and petiole development. Petiole development was inhibited in the presence of Brz. Our results largely contradict the early view that BRs are negative regulators of photomorphogenesis. Our data collectively suggest that light activates the expression of BR biosynthesis genes in the hook region via a phytochrome-signaling pathway and HY5 and that BR biosynthesis is essential for hook opening and petiole development during photomorphogenesis.

[A Case of Liver Metastasis 28 Years after Resection for Gastrointestinal Stromal Tumor of Duodenum].

A 69-year-old woman underwent a pancreaticoduodenectomy at the age of 41 years for a submucosal tumor of duodenum, which was diagnosed as leiomyoma at that time. Twenty eight years later, a liver tumor, which is 10 cm in a diameter, was identified on an abdominal ultrasonography. The left hepatectomy was undertaken. Immunohistochemical examination indicated that the tumor was positive for c-kit and diagnosed as a gastrointestinal stromal tumor(GIST). The pathological reexamination revealed the primary tumor was also positive for c-kit and diagnosed as GIST. Therefore, the liver tumor was considered as a metastasis of the duodenal GIST, which was resected 28 years earlier.

[Laparoscopic Local Gastrectomy for Gastric Schwannoma and Extramurally Developed Gastric GIST].

Among gastric submucosal tumors, neurogenic tumors are considered to be rare diseases. We experienced a case of laparoscopic local gastrectomy of gastric schwannoma coexisting with extramurally developed gastric GIST found accidentally during surgery. A 61-year-old man was pointed out a gastric submucosal tumor with a diameter of 15 mm in a medical checkup. Endoscopic ultrasound-guided fine needle aspiration(EUS-FNA)was performed, and immunostaining showed that c-kit(-), CD34(-), S-100(+), SMA(-), MIB-1<2%. Diagnosis was gastric schwannoma. We performed laparoscopic local gastrectomy. During the surgery another extramural nodule was accidentally found with a diameter of 8 mm at the anterior wall of the gastric body near lesser curvature. Immunostaining showed c-kit(+), CD34(+)and was diagnosed GIST. Because a gastric schwannoma coexisting with GIST is a rare case, we decided to report it by adding discussion with some literatures.

Identification and Characterization of the PEBP Family Genes in Moso Bamboo (Phyllostachys heterocycla).

Moso bamboo is one of the economically most important plants in China. Moso bamboo is a monocarpic perennial that exhibits poor and slow germination. Thus, the flowering often causes destruction of moso bamboo forestry. However, how control of flowering and seed germination are regulated in moso bamboo is largely unclear. In this study, we identified 5 members (PhFT1-5) of the phosphatidyl ethanolamine-binding proteins (PEBP) family from moso bamboo genome that regulate flowering, flower architecture and germination, and characterized the function of these PEBP family genes further in Arabidopsis. Phylogenetic analysis revealed that 3 (PhFT1, PhFT2 and PhFT3), 1 (PhFT4) and 1 (PhFT5) members belong to the TFL1-like clade, FT-like clade, and MFT-like clade, respectively. These PEBP family genes possess all structure necessary for PEBP gene function. The ectopic overexpression of PhFT4 and PhFT5 promotes flowering time in Arabidopsis, and that of PhFT1, PhFT2 and PhFT3 suppresses it. In addition, the overexpression of PhFT5 promotes seed germination rate. Interestingly, the overexpression of PhFT1 suppressed seed germination rate in Arabidopsis. The expression of PhFT1 and PhFT5 is significantly higher in seed than in tissues including leaf and shoot apical meristem, implying their function in seed germination. Taken together, our results suggested that the PEBP family genes play important roles as regulators of flowering and seed germination in moso bamboo and thereby are necessary for the sustainability of moso bamboo forest.

[A Case of Pancreatic Metastasis from Colon Cancer Successfully Treated with Capecitabine/Oxaliplatin plus Bevacizumab].

A 50-year-old man underwent low anterior resection for rectal cancer. The final diagnosis was rectal cancer of pT3N0M0, fStage Ⅱ. CT performed for examination of obstructive jaundice at 17 months after surgery revealed metastatic lesions of the pancreatic head and right lung. By core needle biopsies, the lesions were pathologically diagnosed as metachronous metastases of rectal cancer. Chemotherapy was carried out but was discontinued at 5 courses due to severe side effects. The pancreatic metastasis disappeared after 11 months. As the lung metastasis remained, a right upper lobectomy was performed 1 month later. The patient remains alive without recurrence 6 months after the partial lung resection.

[Primary Small-Cell Carcinoma of the Digestive Tract-An Analysis of Six Cases].

INTRODUCTION: Primary small-cell carcinomas occur commonly in the lungs but rarely in the other organs. We studied the treatment outcomes in 6 cases of primary small-cell carcinoma of the digestive tract at our hospital. PATIENTS: Six patients were diagnosed with small-cell carcinoma of the digestive tract histopathologically and treated at our hospital from September 2000 to December 2018. RESULTS: The average age of the patients was 61.5 years(range: 40-80 years). Patients were 3 men and 3 women. The occurrence sites were the esophagus, stomach, and colon in 1, 2, and 3 patients, respectively. The patient with esophageal cancer underwent chemoradiotherapy without surgery. Other patients, except for 1 patient with colon cancer, underwent adjuvant chemotherapy after the surgery. Two of the 6 patients survived for over 5 years. DISCUSSION: For small-cell carcinomas of the digestive tract with poor prognosis, long-term survival can be expected using multidisciplinary treatments depending on the case.

PtWOX11 acts as master regulator conducting the expression of key transcription factors to induce de novo shoot organogenesis in poplar.

KEY MESSAGE: WUSCHEL-RELATED HOMEOBOX 11 establishes the acquisition of pluripotency during callus formation and accomplishes de novo shoot formation by regulating key transcription factors in poplar. De novo shoot regeneration is a prerequisite for propagation and genetic engineering of elite cultivars in forestry. However, the regulatory mechanism of de novo organogenesis is poorly understood in tree species. We previously showed that WUSCHEL (WUS)-RELATED HOMEOBOX 11 (PtWOX11) of the hybrid poplar clone 84K (Populus alba × P. glandulosa) promotes de novo root formation. In this study, we found that PtWOX11 also regulates de novo shoot regeneration in poplar. The overexpression of PtWOX11 enhanced de novo shoot formation, whereas overexpression of PtWOX11 fused with the transcriptional repressor domain (PtWOX11-SRDX) or reduced expression of PtWOX11 inhibited this process, indicating that PtWOX11 promotes de novo shoot organogenesis. Although PtWOX11 promotes callus formation, overexpression of PtWOX11 and PtWOX11-SRDX also produced increased and decreased numbers of de novo shoots per unit weight, respectively, implying that PtWOX11 promotes de novo shoot organogenesis partially by regulating the intrinsic mechanism of shoot development. RNA-seq and qPCR analysis further revealed that PtWOX11 activates the expression of PLETHORA1 (PtPLT1) and PtPLT2, whose Arabidopsis paralogs establish the acquisition of pluripotency, during incubation on callus-inducing medium. Moreover, PtWOX11 activates the expression of shoot-promoting factors and meristem regulators such as CUP-SHAPED COTYLEDON2 (PtCUC2), PtCUC3, WUS and SHOOT MERISTEMLESS to fulfill shoot regeneration during incubation on shoot-inducing medium. These results suggest that PtWOX11 acts as a central regulator of the expression of key genes to cause de novo shoot formation. Our studies further provide a possible means to genetically engineer economically important tree species for their micropropagation.

Beyond the photocycle-how cryptochromes regulate photoresponses in plants?

Cryptochromes (CRYs) are blue light receptors that mediate light regulation of plant growth and development. Land plants possess various numbers of cryptochromes, CRY1 and CRY2, which serve overlapping and partially redundant functions in different plant species. Cryptochromes exist as physiologically inactive monomers in darkness; photoexcited cryptochromes undergo homodimerization to increase their affinity to the CRY-signaling proteins, such as CIBs (CRY2-interacting bHLH), PIFs (Phytochrome-Interacting Factors), AUX/IAA (Auxin/INDOLE-3-ACETIC ACID), and the COP1-SPAs (Constitutive Photomorphogenesis 1-Suppressors of Phytochrome A) complexes. These light-dependent protein-protein interactions alter the activity of the CRY-signaling proteins to change gene expression and developmental programs in response to light. In the meantime, photoexcitation also changes the affinity of cryptochromes to the CRY-regulatory proteins, such as BICs (Blue-light Inhibitors of CRYs) and PPKs (Photoregulatory Protein Kinases), to modulate the activity, modification, or abundance of cryptochromes and photosensitivity of plants in response to the changing light environment.

New insights into the mechanisms of phytochrome-cryptochrome coaction.

Contents Summary 547 I. Introduction 547 II. Phytochromes mediate light-induced transcription of BICs to inactivate cryptochromes 548 III. PPKs phosphorylate light-signaling proteins and histones to affect plant development 548 IV. Prospect 550 Acknowledgements 550 References 550 SUMMARY: Plants perceive and respond to light signals by multiple sensory photoreceptors, including phytochromes and cryptochromes, which absorb different wavelengths of light to regulate genome expression and plant development. Photophysiological analyses have long revealed the coordinated actions of different photoreceptors, a phenomenon referred to as the photoreceptor coaction. The mechanistic explanations of photoreceptor coactions are not fully understood. The function of direct protein-protein interaction of phytochromes and cryptochromes and common signaling molecules of these photoreceptors, such as SPA1/COP1 E3 ubiquitin ligase complex and bHLH transcription factors PIFs, would partially explain phytochrome-cryptochrome coactions. In addition, newly discovered proteins that block cryptochrome photodimerization or catalyze cryptochrome phosphorylation may also participate in the phytochrome and cryptochrome coaction. This Tansley insight, which is not intended to make a comprehensive review of the studies of photoreceptor coactions, attempts to highlight those recent findings and their possible roles in the photoreceptor coaction.

A CRY-BIC negative-feedback circuitry regulating blue light sensitivity of Arabidopsis.

Cryptochromes are blue light receptors that regulate various light responses in plants. Arabidopsis cryptochrome 1 (CRY1) and cryptochrome 2 (CRY2) mediate blue light inhibition of hypocotyl elongation and long-day (LD) promotion of floral initiation. It has been reported recently that two negative regulators of Arabidopsis cryptochromes, Blue light Inhibitors of Cryptochromes 1 and 2 (BIC1 and BIC2), inhibit cryptochrome function by blocking blue light-dependent cryptochrome dimerization. However, it remained unclear how cryptochromes regulate the BIC gene activity. Here we show that cryptochromes mediate light activation of transcription of the BIC genes, by suppressing the activity of CONSTITUTIVE PHOTOMORPHOGENIC 1 (COP1), resulting in activation of the transcription activator ELONGATED HYPOCOTYL 5 (HY5) that is associated with chromatins of the BIC promoters. These results demonstrate a CRY-BIC negative-feedback circuitry that regulates the activity of each other. Surprisingly, phytochromes also mediate light activation of BIC transcription, suggesting a novel photoreceptor co-action mechanism to sustain blue light sensitivity of plants under the broad spectra of solar radiation in nature.

Molecular basis for blue light-dependent phosphorylation of Arabidopsis cryptochrome 2.

Plant cryptochromes undergo blue light-dependent phosphorylation to regulate their activity and abundance, but the protein kinases that phosphorylate plant cryptochromes have remained unclear. Here we show that photoexcited Arabidopsis cryptochrome 2 (CRY2) is phosphorylated in vivo on as many as 24 different residues, including 7 major phosphoserines. We demonstrate that four closely related Photoregulatory Protein Kinases (previously referred to as MUT9-like kinases) interact with and phosphorylate photoexcited CRY2. Analyses of the ppk123 and ppk124 triple mutants and amiR4k artificial microRNA-expressing lines demonstrate that PPKs catalyse blue light-dependent CRY2 phosphorylation to both activate and destabilize the photoreceptor. Phenotypic analyses of these mutant lines indicate that PPKs may have additional substrates, including those involved in the phytochrome signal transduction pathway. These results reveal a mechanism underlying the co-action of cryptochromes and phytochromes to coordinate plant growth and development in response to different wavelengths of solar radiation in nature.