Long-distance transport of sucrose in source leaves promotes sink root growth by the EIN3-SUC2 module.

In most plants, sucrose, a major storage sugar, is transported into sink organs to support their growth. This key physiological process is dependent on the function of sucrose transporters. Sucrose export from source tissues is predominantly controlled through the activity of SUCROSE TRANSPORTER 2 (SUC2), required for the loading of sucrose into the phloem of Arabidopsis plants. However, how SUC2 activity is controlled to support root growth remains unclear. Glucose is perceived via the function of HEXOKINASE 1 (HXK1), the only known nuclear glucose sensor. HXK1 negatively regulates the stability of ETHYLENE-INSENSITIVE3 (EIN3), a key ethylene/glucose interaction component. Here we show that HXK1 functions upstream of EIN3 in the regulation of root sink growth mediated by glucose signaling. Furthermore, the transcription factor EIN3 directly inhibits SUC2 activity by binding to the SUC2 promoter, regulating glucose signaling linked to root sink growth. We demonstrate that these molecular components form a HXK1-EIN3-SUC2 module integral to the control of root sink growth. Also, we demonstrate that with increasing age, the HXK1-EIN3-SUC2 module promotes sucrose phloem loading in source tissues thereby elevating sucrose levels in sink roots. As a result, glucose signaling mediated-sink root growth is facilitated. Our findings thus establish a direct molecular link between the HXK1-EIN3-SUC2 module, the source-to sink transport of sucrose and root growth.

Cytosolic Invertase-Mediated Root Growth Is Feedback Regulated by a Glucose-Dependent Signaling Loop.

The disaccharide Suc cannot be utilized directly; rather, it is irreversibly hydrolyzed by invertase to the hexoses Glc and Fru to shape plant growth. In this context, Glc controls the stability of the transcription factor Ethylene-Insensitive3 (EIN3) via the function of Hexokinase1 (HXK1), a Glc sensor. Thus, invertase, especially the major neutral cytosolic invertase (CINV), constitutes a key point of control for plant growth. However, the cognate regulatory mechanisms that modulate CINV activity remain unclear. Here, we demonstrate that in Arabidopsis (Arabidopsis thaliana), EIN3 binds directly to both the promoters of Production of Anthocyanin Pigment1 (PAP1) and Phosphatidylinositol Monophosphate 5-Kinase 9 (PIP5K9), repressing and enhancing, respectively, their expression. Subsequently, PAP1 binds directly to and promotes transcription of the Cytosolic Invertase1 (CINV1) promoter, while PIP5K9 interacts with and negatively regulates CINV1. The accumulated CINV1 subsequently hydrolyzes Suc, releasing the sequestered signaling cue, Glc, which has been shown to negatively regulate the stability of EIN3 via HXK1. We conclude that a CINV1-Glc-HXK1-EIN3-PAP1/PIP5K9-CINV1 loop contributes to the modulation of CINV1 activity regulating root growth by Glc signaling.

Arabidopsis ANGUSTIFOLIA3 (AN3) is associated with the promoter of CONSTITUTIVE PHOTOMORPHOGENIC1 (COP1) to regulate light-mediated stomatal development.

Light signals are perceived by multiple photoreceptors that converge to suppress the RING E3 ubiquitin ligase CONSTITUTIVE PHOTOMORPHOGENIC1 (COP1) for the regulation of stomatal development. Thus, COP1 is a point of integration between light signaling and stomatal patterning. However, how light signaling is collected into COP1 for the production and spacing of stomata is still unknown. Here, we report that the loss-of-function mutant of ANGUSTIFOLIA3 (AN3) delays asymmetric cell division, which leads to decreased stomatal index. Furthermore, overexpression of AN3 accelerates asymmetric cell division, which results in clusters of stomata. In addition, the stomatal development through AN3 regulation is mediated by light signaling. Finally, we find that an3 is a light-signaling mutant, and that AN3 protein is light regulated. Self-activation by AN3 contributes to the control of AN3 expression. Thus, AN3 is a point of collection between light signaling and stomatal patterning. Target-gene analysis indicates that AN3 is associated with COP1 promoter for the regulation of light-controlling stomatal development. Together, these components for regulating stomatal development form an AN3-COP1-E3 ubiquitin ligase complex, allowing the integration of light signaling into the production and spacing of stomata.

Feedback loop promotes sucrose accumulation in cotyledons to facilitate sugar-ethylene signaling-mediated, etiolated-seedling greening.

De-etiolation is indispensable for seedling survival and development. However, how sugars regulate de-etiolation and how sugars induce ethylene (ET) for seedlings to grow out of soil remain elusive. Here, we reveal how a sucrose (Suc) feedback loop promotes de-etiolation by inducing ET biosynthesis. Under darkness, Suc in germinating seeds preferentially induces 1-amino-cyclopropane-1-carboxylate synthase (ACS7; encoding a key ET biosynthesis enzyme) and associated ET biosynthesis, thereby activating ET core component ETHYLENE-INSENSITIVE3 (EIN3). Activated EIN3 directly inhibits the function of Suc transporter 2 (SUC2; a major Suc transporter) to block Suc export from cotyledons and thereby elevate Suc accumulation of cotyledons to induce ET. Under light, ET-activated EIN3 directly inhibits the function of phytochrome A (phyA; a de-etiolation inhibitor) to promote de-etiolation. We therefore propose that under darkness, the Suc feedback loop (Suc-ACS7-EIN3-|SUC2-Suc) promotes Suc accumulation in cotyledons to guarantee ET biosynthesis, facilitate de-etiolation, and enable seedlings to grow out of soil.

Clinical Characteristics of Pediatric Cases of COVID-19 in Hunan, China: A Retrospective, Multi-Center Case Series.

Objective: Aimed to investigate the epidemiological characteristics, clinical features, treatment, and short-term prognosis of COVID-19 in children. Methods: Retrospective analysis was conducted in 48 children with COVID-19 admitted to 12 hospitals in eight cities in Hunan province, China, from January 26, 2020 to June 30, 2020. Results: Of the 48 cases, Familial clusters were confirmed for 46 children (96%). 16 (33%) were imported from other provinces. There were 11 (23%) asymptomatic cases. only 2 cases (4%) were severe. The most common symptom was fever (n = 20, 42%). Other symptoms included cough (n = 19, 40%), fatigue (n = 8, 17%), and diarrhea (n = 5, 10%). In the early stage, the total peripheral blood leukocytes count increased in 3(6%) cases and the lymphocytes count decreased in 5 (10%) cases. C-reactive protein and procalcitonin were elevated respectively in 3 (6%) cases and 2 (4%) cases. There were abnormal chest CT changes in 22 (46%) children, including 15 (68%) with patchy ground glass opacity, 5 (22%) with consolidation, and 2 (10%) with mixed shadowing. In addition to supportive treatment, antiviral therapy was received by 41 (85%) children, 11 (23%) patients were treated with antibiotics, and 2 (4%) were treated with methylprednisolone and intravenous immunoglobulin. Compared to 2 weeks follow-up, one child developed low fever and headache during the 4 weeks follow-up, 3 (6%) children had runny noses, one of them got mild cough, and 4 (12%) children had elevated white blood cells and lymphocytes. However, LDH and CK increased at 2 weeks and 4 weeks follow-up. 2 weeks follow-up identified normal chest radiographs in 33 (69%) pediatric patients. RT-PCR detection of SARS-CoV-2 was negative in all follow-up patients at 2 and 4 weeks follow-up. All 48 pediatric patients were visited by calling after 1 year of discharge. Conclusions: Most cases of COVID-19 in children in Hunan province were asymptomatic, mild, or moderate. Close family contact was the main route of infection. It appeared that the younger the patient, the less obvious their symptoms. Epidemiological history, nucleic acid test, and chest imaging were important tools for diagnosis in children.

Glucose- and sucrose-signaling modules regulate the Arabidopsis juvenile-to-adult phase transition.

CINV1, converting sucrose into glucose and fructose, is a key entry of carbon into cellular metabolism, and HXK1 functions as a pivotal sensor for glucose. Exogenous sugars trigger the Arabidopsis juvenile-to-adult phase transition via a miR156A/SPL module. However, the endogenous factors that regulate this process remain unclear. In this study, we show that sucrose specifically induced the PAP1 transcription factor directly and positively controls CINV1 activity. Furthermore, we identify a glucose feed-forward loop (sucrose-CINV1-glucose-HXK1-miR156-SPL9-PAP1-CINV1-glucose) that controls CINV1 activity to convert sucrose into glucose signaling to dynamically control the juvenile-to-adult phase transition. Moreover, PAP1 directly binds to the SPL9 promoter, activating SPL9 expression and triggering the sucrose-signaling-mediated juvenile-to-adult phase transition. Therefore, a glucose-signaling feed-forward loop and a sucrose-signaling pathway synergistically regulate the Arabidopsis juvenile-to-adult phase transition. Collectively, we identify a molecular link between the major photosynthate sucrose, the entry point of carbon into cellular metabolism, and the plant juvenile-to-adult phase transition.

Sucrose Signaling Regulates Anthocyanin Biosynthesis Through a MAPK Cascade in Arabidopsis thaliana.

Anthocyanin accumulation specifically depends on sucrose (Suc) signaling. However, the molecular basis of this process remains unknown. In this study, in vitro pull-down assays identified ETHYLENE-INSENSITIVE3 (EIN3), a component of both sugar signaling or/and metabolism. This protein interacted with YDA, and the physiological relevance of this interaction was confirmed by in planta co-immunoprecipitation, yeast two-hybrid (Y2H) assay, and bimolecular fluorescence complementation. Ethylene insensitive3-like 1 (eil1) ein3 double-mutant seedlings, but not ein3-1 seedlings, showed anthocyanin accumulation. Furthermore, ein3-1 suppressed anthocyanin accumulation in yda-1 plants. Thus, EMB71/YDA-EIN3-EIL1 may form a sugar-mediated gene cascade integral to the regulation of anthocyanin accumulation. Moreover, the EMB71/YDA-EIN3-EIL1 gene cascade module directly targeted the promoter of Transparent Testa 8 (TT8) by direct EIN3 binding. Collectively, our data inferred a molecular model where the signaling cascade of the YDA-EIN3-TT8 appeared to target TT8 via EIN3, thereby modulating Suc signaling-mediated anthocyanin accumulation.

[Molecular mapping of two semidwarf genes in an indica rice variety Aitaiyin3 (Oryza sativa L.)].

The rice dwarf variety Aitaiyin3 is derived from a semidwarf cultivar Taiyin1. Genetic analysis indicated that the dwarf phenotype in Aitaiyin3 is involved in two recessive loci. Using bulk analysis with SSR markers, the two loci were located on the chromosome 1 and chromosome 4, respectively. Moreover, the allelism test showed that the locus on the chromosome 1 is allelic to the semidwarf gene sd1, while the other one is a new locus, here was named as sdt2. Further molecular mapping showed that sd1 was linked with SSR markers in the order of RM297-RM302-RM212-OSR3-sd1 with genetic distances of 4.7 cM, 0 cM, 0.8 cM and 0 cM, respectively. The linkage relationship of sdt2 with five SSR markers was SSR332-RM1305-sdt2-RM5633-RM307-RM401 with genetic distances of 11.6 cM, 3.8 cM, 0.4 cM, 0 cM and 0.4 cM, respectively.