Light Controls Protein Localization through Phytochrome-Mediated Alternative Promoter Selection.

Alternative promoter usage is a proteome-expanding mechanism that allows multiple pre-mRNAs to be transcribed from a single gene. The impact of this mechanism on the proteome and whether it is positively exploited in normal organismal responses remain unclear. We found that the plant photoreceptor phytochrome induces genome-wide changes in alternative promoter selection in Arabidopsis thaliana. Through this mechanism, protein isoforms with different N termini are produced that display light-dependent differences in localization. For instance, shade-grown plants accumulate a cytoplasmic isoform of glycerate kinase (GLYK), an essential photorespiration enzyme that was previously thought to localize exclusively to the chloroplast. Cytoplasmic GLYK constitutes a photorespiratory bypass that alleviates fluctuating light-induced photoinhibition. Therefore, phytochrome controls alternative promoter selection to modulate protein localization in response to changing light conditions. This study suggests that alternative promoter usage represents another ubiquitous layer of gene expression regulation in eukaryotes that contributes to diversification of the proteome.

High-intensity light promotes adaptive divergence of photosynthetic traits between sun-exposed and shaded populations in Saxifraga fortunei.

PREMISE: Light is essential for plants, and local populations exhibit adaptive photosynthetic traits depending on their habitats. Although plastic responses in morphological and/or physiological characteristics to different light intensities are well known, adaptive divergence with genetic variation remains to be explored. This study focused on Saxifraga fortunei (Saxifragaceae) growing in sun-exposed and shaded habitats. METHODS: We measured the leaf anatomical structure and photosynthetic rate of plants grown in their natural habitats and in a common greenhouse (high- and low-intensity light experimental sites). To assess differences in ecophysiological tolerance to high-intensity light between the sun and shade types, we evaluated the level of photoinhibition of photosystem II and the leaf mortality rate under high-intensity light conditions. In addition, population genetic analysis was conducted to investigate phylogenetic origins. RESULTS: Clear phenotypic differences were found between the sun and shade types despite their recent phylogenetic origin. The leaf anatomical structure and photosynthetic rate showed plastic changes in response to growing conditions. Moreover, the sun type had a well-developed palisade parenchyma and a higher photosynthetic rate, which were genetically fixed, and a lower level of photoinhibition under high-intensity light. CONCLUSIONS: Our findings demonstrate that light intensity is a selective pressure that can rapidly promote phenotypic divergence between the sun and shade types. While phenotypic changes in multiple photosynthetic traits were plastic, genetic divergence in specific traits related to adaptation to high-intensity light would be fundamental for ecotypic divergence to different light regimes.

A tonoplast-localized magnesium transporter is crucial for stomatal opening in Arabidopsis under high Mg2+ conditions.

Plant stomata play an important role in CO2 uptake for photosynthesis and transpiration, but the mechanisms underlying stomatal opening and closing under changing environmental conditions are still not completely understood. Through large-scale genetic screening, we isolated an Arabidopsis mutant (closed stomata2 (cst2)) that is defective in stomatal opening. We cloned the causal gene (MGR1/CST2) and functionally characterized this gene. The mutant phenotype was caused by a mutation in a gene encoding an unknown protein with similarities to the human magnesium (Mg2+ ) efflux transporter ACDP/CNNM. MGR1/CST2 was localized to the tonoplast and showed transport activity for Mg2+ . This protein was constitutively and highly expressed in guard cells. Knockout of this gene resulted in stomatal closing, decreased photosynthesis and growth retardation, especially under high Mg2+ conditions, while overexpression of this gene increased stomatal opening and tolerance to high Mg2+ concentrations. Furthermore, guard cell-specific expression of MGR1/CST2 in the mutant partially restored its stomatal opening. Our results indicate that MGR1/CST2 expression in the leaf guard cells plays an important role in maintaining cytosolic Mg2+ concentrations through sequestering Mg2+ into vacuoles, which is required for stomatal opening, especially under high Mg2+ conditions.

Phototropin2 Contributes to the Chloroplast Avoidance Response at the Chloroplast-Plasma Membrane Interface.

Blue-light-induced chloroplast movements play an important role in maximizing light utilization for photosynthesis in plants. Under a weak light condition, chloroplasts accumulate to the cell surface to capture light efficiently (chloroplast accumulation response). Conversely, chloroplasts escape from strong light and move to the side wall to reduce photodamage (chloroplast avoidance response). The blue light receptor phototropin (phot) regulates these chloroplast movements and optimizes leaf photosynthesis by controlling other responses in addition to chloroplast movements. Seed plants such as Arabidopsis (Arabidopsis thaliana) have phot1 and phot2. They redundantly mediate phototropism, stomatal opening, leaf flattening, and the chloroplast accumulation response. However, the chloroplast avoidance response is induced by strong blue light and regulated primarily by phot2. Phots are localized mainly on the plasma membrane. However, a substantial amount of phot2 resides on the chloroplast outer envelope. Therefore, differentially localized phot2 might have different functions. To determine the functions of plasma membrane- and chloroplast envelope-localized phot2, we tethered it to these structures with their respective targeting signals. Plasma membrane-localized phot2 regulated phototropism, leaf flattening, stomatal opening, and chloroplast movements. Chloroplast envelope-localized phot2 failed to mediate phototropism, leaf flattening, and the chloroplast accumulation response but partially regulated the chloroplast avoidance response and stomatal opening. Based on the present and previous findings, we propose that phot2 localized at the interface between the plasma membrane and the chloroplasts is required for the chloroplast avoidance response and possibly for stomatal opening as well.

Regulation of Photosynthetic Carbohydrate Metabolism by a Raf-Like Kinase in the Liverwort Marchantia polymorpha.

To optimize growth and development, plants monitor photosynthetic activities and appropriately regulate various cellular processes. However, signaling mechanisms that coordinate plant growth with photosynthesis remain poorly understood. To identify factors that are involved in signaling related to photosynthetic stimuli, we performed a phosphoproteomic analysis with Marchantia polymorpha, an extant bryophyte species in the basal lineage of land plants. Among proteins whose phosphorylation status changed differentially between dark-treated plants and those after light irradiation but failed to do so in the presence of a photosynthesis inhibitor, we identified a B4-group Raf-like kinase, named PHOTOSYNTHESIS-RELATED RAF (MpPRAF). Biochemical analyses confirmed photosynthesis-activity-dependent changes in the phosphorylation status of MpPRAF. Mutations in the MpPRAF gene resulted in growth retardation. Measurement of carbohydrates demonstrated both hyper-accumulation of starch and reduction of sucrose in Mppraf mutants. Neither inhibition of starch synthesis nor exogenous supply of sucrose alleviated the growth defect, suggesting serious impairment of Mppraf mutants in both the synthesis of sucrose and the repression of its catabolism. As a result of the compromised photosynthate metabolism, photosynthetic electron transport was downregulated in Mppraf mutants. A mutated MpPRAF with a common amino acid substitution for inactivating kinase activity was unable to rescue the Mppraf mutant defects. Our results provide evidence that MpPRAF is a photosynthesis signaling kinase that regulates sucrose metabolism.

Light-induced chloroplast movements in Oryza species.

Light-induced chloroplast movements control efficient light utilization in leaves, and thus, are essential for leaf photosynthesis and biomass production under fluctuating light conditions. Chloroplast movements have been intensively analyzed using wild-type and mutant plants of Arabidopsis thaliana. The molecular mechanism and the contribution to biomass production were elucidated. However, the knowledge of chloroplast movements is very scarce in other plant species, especially grass species including crop plants. Because chloroplast movements are efficient strategy to optimize light capture in leaves and thus promote leaf photosynthesis and biomass, analysis of chloroplast movements in crops is required for biomass production. Here, we analyzed chloroplast movements in a wide range of cultivated and wild species of genus Oryza. All examined Oryza species showed the blue-light-induced chloroplast movements. However, O. sativa and its ancestral species O. rufipogon, both of which are AA-genome species and usually grown in open condition where plants are exposed to full sunlight, showed the much weaker chloroplast movements than Oryza species that are usually grown under shade or semi-shade conditions, including O. officinalis, O. eichingeri, and O. granulata. Further detailed analyses of different O. officinalis accessions, including sun, semi-shade, and shade accessions, indicated that the difference in chloroplast movement strength between domesticated rice plants and wild species might result from the difference in habitat, and the shape of mesophyll chlorenchyma cells. The findings of this study provide useful information for optimizing Oryza growth conditions, and lay the groundwork for improving growth and yield in staple food crop Oryza sativa.

Chloroplast Accumulation Response Enhances Leaf Photosynthesis and Plant Biomass Production.

Under high light intensity, chloroplasts avoid absorbing excess light by moving to anticlinal cell walls (avoidance response), but under low light intensity, chloroplasts accumulate along periclinal cell walls (accumulation response). In most plant species, these responses are induced by blue light and are mediated by the blue light photoreceptor, phototropin, which also regulates phototropism, leaf flattening, and stomatal opening. These phototropin-mediated responses could enhance photosynthesis and biomass production. Here, using various Arabidopsis (Arabidopsis thaliana) mutants deficient in chloroplast movement, we demonstrated that the accumulation response enhances leaf photosynthesis and plant biomass production. Conspicuously, phototropin2 mutant plants specifically defective in the avoidance response but not in other phototropin-mediated responses displayed a constitutive accumulation response irrespective of light intensities, enhanced leaf photosynthesis, and increased plant biomass production. Therefore, our findings provide clear experimental evidence of the importance of the chloroplast accumulation response in leaf photosynthesis and biomass production.

Stomatal response to blue light in crassulacean acid metabolism plants Kalanchoe pinnata and Kalanchoe daigremontiana.

Blue light (BL) is a fundamental cue for stomatal opening in both C3 and C4 plants. However, it is unknown whether crassulacean acid metabolism (CAM) plants open their stomata in response to BL. We investigated stomatal BL responses in the obligate CAM plants Kalanchoe pinnata and Kalanchoe daigremontiana that characteristically open their stomata at night and close them for part of the day, as contrasted with C3 and C4 plants. Stomata opened in response to weak BL superimposed on background red light in both intact leaves and detached epidermal peels of K. pinnata and K. daigremontiana. BL-dependent stomatal opening was completely inhibited by tautomycin and vanadate, which repress type 1 protein phosphatase and plasma membrane H+-ATPase, respectively. The plasma membrane H+-ATPase activator fusicoccin induced stomatal opening in the dark. Both BL and fusicoccin induced phosphorylation of the guard cell plasma membrane H+-ATPase in K. pinnata. These results indicate that BL-dependent stomatal opening occurs in the obligate CAM plants K. pinnata and K. daigremontiana independently of photosynthetic CO2 assimilation mode.

High Mitochondrial Genome Diversity and Intricate Population Structure of Bursaphelenchus xylophilus in Kyushu, Japan.

Mitogenomic diversity and genetic population structure of the pinewood nematode (PWN) Bursaphelenchus xylophilus inhabiting Kyushu, Japan were analyzed. A method for performing long PCR using single nematodes and sequencing nematode mitochondrial genomes individually is presented here. About 8 kb (∼55%) of the complete mitochondrial genome was successfully obtained from 285 individuals collected from 12 populations. The 158 single nucleotide polymorphisms detected corresponded to 30 haplotypes, clearly classified into two clades. Haplotype diversity was 0.83, evidencing a remarkable high diversity within Kyushu. The high genetic differentiation among the 12 populations (0.331) might be due to past invasion and expansion routes of PWN in northeastern and southeastern Kyushu. The distinct genetic composition of populations within the northwestern, central western, and southwestern Kyushu seems to be mostly related to the extinction of pine forests and long-range migration of PWN due to human activity. Overall, direct long PCR and sequencing of single nematode individuals are effective methods for investigating mitochondrial polymorphisms, and these are effective tools for PWN population genetics and other intraspecific studies.

Brassinosteroid Involvement in Arabidopsis thaliana Stomatal Opening.

Stomata within the plant epidermis regulate CO2 uptake for photosynthesis and water loss through transpiration. Stomatal opening in Arabidopsis thaliana is determined by various factors, including blue light as a signal and multiple phytohormones. Plasma membrane transporters, including H+-ATPase, K+ channels and anion channels in guard cells, mediate these processes, and the activities and expression levels of these components determine stomatal aperture. However, the regulatory mechanisms involved in these processes are not fully understood. In this study, we used infrared thermography to isolate a mutant defective in stomatal opening in response to light. The causative mutation was identified as an allele of the brassinosteroid (BR) biosynthetic mutant dwarf5. Guard cells from this mutant exhibited normal H+-ATPase activity in response to blue light, but showed reduced K+ accumulation and inward-rectifying K+ (K+in) channel activity as a consequence of decreased expression of major K+in channel genes. Consistent with these results, another BR biosynthetic mutant, det2-1, and a BR receptor mutant, bri1-6, exhibited reduced blue light-dependent stomatal opening. Furthermore, application of BR to the hydroponic culture medium completely restored stomatal opening in dwarf5 and det2-1 but not in bri1-6. However, application of BR to the epidermis of dwarf5 did not restore stomatal response. From these results, we conclude that endogenous BR acts in a long-term manner and is required in guard cells with the ability to open stomata in response to light, probably through regulation of K+in channel activity.

Functional characterization of blue-light-induced responses and PHOTOTROPIN 1 gene in Welwitschia mirabilis.

The blue light (BL) receptor phototropin (phot) is specifically found in green plants; it regulates various BL-induced responses such as phototropism, chloroplast movement, stomatal opening, and leaf flattening. In Arabidopsis thaliana, two phototropins--phot1 and phot2--respond to blue light in overlapping but distinct ways. These BL-receptor-mediated responses enhance the photosynthetic activity of plants under weak light and minimize photodamage under strong light conditions. Welwitschia mirabilis Hook.f. found in the Namib Desert, and it has adapted to severe environmental stresses such as limiting water and strong sunlight. Although the plant has physiologically and ecologically unique features, it is unknown whether phototropin is functional in this plant. In this study, we assessed the functioning of phot-mediated BL responses in W. mirabilis. BL-dependent phototropism and stomatal opening was observed but light-dependent chloroplast movement was not detected. We performed a functional analysis of the PHOT1 gene of W. mirabilis, WmPHOT1, in Arabidopsis thaliana. We generated transgenic A. thaliana lines expressing WmPHOT1 in a phot1 phot2 double mutant background. Several Wmphot1 transgenic plants showed normal growth, although phot1 phot2 double mutant plants showed stunted growth. Furthermore, Wmphot1 transgenic plants showed normal phot1-mediated responses including phototropism, chloroplast accumulation, stomatal opening, and leaf flattening, but lacked the chloroplast avoidance response that is specifically mediated by phot2. Thus, our findings indicate that W. mirabilis possesses typical phot-mediated BL responses that were at least partially mediated by functional phototropin 1, an ortholog of Atphot1.

Early effects of oral administration of esomeprazole and omeprazole on the intragastric pH.

BACKGROUND/AIMS: The aim of our study was to investigate the inhibitory effects on gastric acid secretion of a single oral dose of a proton pump inhibitor, esomeprazole 20 mg and omeprazole 20 mg. METHODOLOGY: A total of 14 Helicobacter pylori-negative male subjects participated in this study. Intragastric pH was monitored continuously for 6 hours after a single oral dose of omeprazole 20 mg and a single oral dose of esomeprazole 20 mg. Each administration was separated by a 7-day washout period. RESULTS: During the 6-hour study period, the average pH after administration of esomeprazole was higher than that after the administration of omeprazole. Also during the 6-hour study period, each of pH > 2, 3, 3.5, 4, and 5 was maintained for a longer duration after administration of esomeprazole 20 mg than after administration of omeprazole 20 mg (median: 75.4% vs. 53.8%, p = 0.0138; 52.1% vs. 33.4%, p = 0.0188; 45.8% vs. 28.2%, p = 0.0262; 42.5% vs. 20.7%, p = 0.0414; 35.8% vs. 11.6%, p = 0.0262; respectively). CONCLUSIONS: In Helicobacter pylori-negative healthy male subjects, single oral administration of esomeprazole 20 mg increased the intragastric pH more rapidly than single oral administration of omeprazole 20 mg.

Comparative study of the QUEST questionnaire and GerdQ questionnaire for Japanese students.

BACKGROUND/AIMS: The aim of this study was to comparatively examine the convenience of use of the QUEST and GerdQ questionnaires as self-administered diagnostic instruments. METHODOLOGY: This was a two-way crossover study conducted from December 2011 to April 2012. The subjects were 70 third-year nursing students of Yokohama Soei University in Yokohama, Japan. They were randomly assigned to fill in either of the study questionnaires first, and then the other on a later. RESULTS: A significant difference was observed in the questionnaire completion time between the QUEST and GerdQ questionnaires (125.5 vs. 44 seconds, P < 0.0001) and also in the number of subjects asking questions while completing the questionnaires (26 vs. 1 subject, respectively: P < 0.0001). To detect GERD based on a QUEST score of ≥4, ROC analysis revealed an area under the curve for the GerdQ score of 0.616. The optimal cutoff value of the GerdQ score was 6, and the sensitivity and specificity calculated using this cutoff value were 0.842 and 0.312, respectively. CONCLUSIONS: This study revealed that Japanese subjects may find it easier to complete the GerdQ than the QUEST questionnaire.

Effects of ramosetron oral disintegrating tablets on gastric emptying: crossover study using the 13C-acetic acid breath test.

BACKGROUND/AIMS: Ramosetron is a new selective 5-hydroxytryptamine type 3 (5-HT3) receptor antagonist that reportedly has more potent antiemetic effects than other 5-HT3 receptor antagonists. The aim of this study was to determine the effect of ramosetron pretreatment on gastric emptying using the 13C-acetic acid breath test. METHODOLOGY: Ten healthy male and female volunteers participated in this randomized, twoway crossover study. After they had fasted overnight, the subjects were randomly assigned to receive 0.1 mg ramosetron 1 hour before ingestion of a test meal (200 kcal per 200 mL, containing 100 mg 13C acetate) or to receive the test meal alone. Under both conditions, breath samples were collected for 150 min following ingestion of the meal. Statistical comparison of the parameters between the two test conditions was performed. RESULTS: No significant differences in the calculated parameters, including T 1/2, T lag, GEC or ß and κ, were observed between the two test conditions. CONCLUSIONS: The present study revealed that 0.1 mg ramosetron had no significant effect on the rate of gastric emptying. Thus, our results suggest that ramosetron can be administered safely, without gastrointestinal adverse effects, even to terminal cancer patients with delayed or accelerated gastric emptying abnormality.

Correlation between gastric transit time measured by video capsule endoscopy and gastric emptying determined by the continuous real-time 13C breath test (BreathID system).

BACKGROUND/AIMS: The aim of this study was to determine the possible existence of a correlation between the gastric transit time (GTT) measured by video capsule endoscopy (VCE) and the parameters of gastric emptying determined using 13C breath test (BreathID system). METHODS: Eight healthy male volunteers participated in this randomized, two-way crossover study. The subjects were randomly assigned to undergo VCE using the PillCam SB capsule endoscopy system or the 13C breath test for 4 hours after a test meal (400 kcal per 400 mL) containing 100 mg of 13C acetic acid administered after overnight fasting. The VCE images were analyzed and the GTT was determined using the proprietary RAPID software. The parameters, namely T lag, T 1/2 and GEC were calculated using the Oridion Research Software (ß version). The GTT measured by VCE and the parameters of gastric emptying were compared statistically. RESULTS: No significant correlation was observed between the GTT and T lag (p = 0.5263), T 1/2 (p = 0.4100) or GEC (p = 0.2410), as determined by calculation of the Spearman's rank correlation coefficient. CONCLUSIONS: GTT measured by VCE cannot serve as asubstitute for the gastric emptying time measured bythe 13C breath test.

Protective effect of lactoferrin on acute acid reflux-induced esophageal mucosal damage.

BACKGROUND/AIMS: The natural immunomodulator lactoferrin is known to possess anti-inflammatory effects. However, there have been no studies examining the mode of action of lactoferrin in protecting the esophageal mucosa against damage. We investigated the effect of lactoferrin on gastric acid secretion and in protecting against acute acid reflux-induced esophagitis in rats. METHODOLOGY: Male Wistar rats aged 8 weeks, weighing 210-240 g, were used for all the experiments. A gastric perfusion system was installed using the method of Ghosh et al. Lactoferrin was administered once via the caudate vein, starting 24 hours before an acute acid reflux (treatment mode), or saline (control). Statistical comparison of the parameters between the two test conditions was performed. RESULTS: No significant differences in basal or stimulated gastric acid secretion, or in the serum gastrin level were observed between the two test conditions. Esophageal damage was attenuated by lactoferrin in a dose-dependent manner, as reflected by the improvement in the esophageal tissue weight and macroscopic scores. Significant reductions in the histological scores, myeloperoxidase activity and the levels of proinflammatory cytokines, tumor necrosis factor-α and interleukin-1ß were also observed following lactoferrin administration. CONCLUSIONS: We concluded that lactoferrin exerts a protective effect against acute acid reflux-induced esophageal damage in rats.

Early effect of oral administration of omeprazole with mosapride as compared with those of omeprazole alone on the intragastric pH.

BACKGROUND: The ideal medication for acid-related diseases should have a rapid onset of action to promote hemostasis and cause efficient resolution of symptoms. The aim of our study was to comparatively investigate the inhibitory effect on gastric acid secretion of a single oral administration of omeprazole plus mosapride with that of omeprazole alone. METHODS: Ten Helicobacter pylori-negative male subjects participated in this randomized, two-way crossover study. Intragastric pH was monitored continuously for 6 hours after a single oral administration of omeprazole 20 mg or that of omeprazole 20 mg plus mosapride 5 mg (the omeprazole being administered one hour after the mosapride). Each administration was separated by a 7-days washout period. RESULTS: The average pH during the 6-hour period after administration of omeprazole 20 mg plus mosapride 5 mg was higher than that after administration of omeprazole 20 mg alone (median: 3.22 versus 4.21, respectively; p = 0.0247). CONCLUSIONS: In H. pylori -negative healthy male subjects, an oral dose of omeprazole 20 mg plus mosapride 5 mg increased the intragastric pH more rapidly than omeprazole 20 mg alone.

Risk factors for colonic diverticular hemorrhage: Japanese multicenter study.

BACKGROUND AND AIM: Diverticular hemorrhage is the common cause of lower gastrointestinal bleeding, and its incidence has been increasing in Japan. However, the exact cause of diverticular hemorrhage is not well understood. We investigated the risk factors for diverticular hemorrhage. METHODS: We selected 103 patients with diverticular hemorrhage as cases and patients with colonic diverticulosis without a history of bleeding were selected as control subjects, exactly matched for age and gender. We collected the data from the medical records of each of the patients, such as those related to the comorbidities, medications and findings of colonoscopy, and conducted a matched case-control study to analyze the risk factors for diverticular hemorrhage. RESULTS: Both groups were composed of 75 men and 28 women. The median age of the patients in both groups was 72.0 years (47.0-87.0). The body weight (p = 0.0065), body mass index (p = 0.006), prevalence of hypertension (p = 0.0242), prevalence of ischemic heart disease (p = 0.0015), and frequency of use of low-dose aspirin (p = 0.042) were significantly different between the two groups. The percentage of patients with bilateral diverticula, that is, diverticula on both the right and left hemicolon, was significantly higher in the diverticular hemorrhage group (p = 0.0011). Multiple regression analysis identified only the diverticular location as being significantly associated with the risk of diverticular hemorrhage (p = 0.0021). CONCLUSIONS: Only the diverticular location (bilateral) was found to be an independent risk factor for diverticular hemorrhage.

A new non-invasive modality for recording sequential images and the pH of the small bowel.

BACKGROUND/AIMS: Before the introduction of capsule endoscopy and double-balloon endoscopy, there were no effective modalities for reliable evaluation of the small bowel. Recently, the SmartPill, a wireless pH/ pressure recording capsule, has been utilized to measure the whole gut transit time. However, there are few studies on the small bowel pH. The aim of this study was to investigate the relationship between small bowel disease and the small bowel pH, we designed a new modality, the 'pH capsule', to non-invasively record sequential images and the pH. METHODOLOGY: Ten healthy male volunteers swallowed the 'pH capsule' with 50mL of water. The 'pH capsule' transmitted the acquired images and the pH to the recorder unit located outside the body for about ten hours while the subject was fasting. RESULTS: All subjects completed this study. The intragastric pH was low and the pH in the whole small intestine was 7.61, 7.55: 7.2-8.1 (mean, median: range). The pH value increased from the duodenum to the terminal ileum (p<0.0001). CONCLUSIONS: We could non-invasively monitor sequential images and the pH of the small intestine with this new modality. The 'pH capsule' is expected to become a valuable tool for clinical assessment of the small bowel.

A PSTAIRE-type cyclin-dependent kinase controls light responses in land plants.

Light is a critical signal perceived by plants to adapt their growth rate and direction. Although many signaling components have been studied, how plants respond to constantly fluctuating light remains underexplored. Here, we showed that in the moss Physcomitrium (Physcomitrella) patens, the PSTAIRE-type cyclin-dependent kinase PpCDKA is dispensable for growth. Instead, PpCDKA and its homolog in Arabidopsis thaliana control light-induced tropisms and chloroplast movements by probably influencing the cytoskeleton organization independently of the cell cycle. In addition, lower PpCDKA kinase activity was required to elicit light responses relative to cell cycle regulation. Thus, our study suggests that plant CDKAs may have been co-opted to control multiple light responses, and owing to the bistable switch properties of PSTAIRE-type CDKs, the noncanonical functions are widely conserved for eukaryotic environmental adaptation.