Fang Bao

Cytokinins can act as suppressors of nitric oxide in Arabidopsis

Maintaining nitric oxide (NO) homeostasis is essential for normal plant physiological processes. However, very little is known about the mechanisms of NO modulation in plants. Here, we report a unique mechanism for the catabolism of NO based on the reaction with the plant hormone cytokinin. We screened for NO-insensitive mutants in Arabidopsis and isolated two allelic lines, cnu1-1 and 1–2 (continuous NO-unstressed 1), that were identified as the previously reported altered meristem program 1 (amp1) and as having elevated levels of cytokinins. A double mutant of cnu1-2 and nitric oxide overexpression 1 (nox1) reduced the severity of the phenotypes ascribed to excess NO levels as did treating the nox1 line with trans-zeatin, the predominant form of cytokinin in Arabidopsis. We further showed that peroxinitrite, an active NO derivative, can react with zeatin in vitro, which together with the results in vivo suggests that cytokinins suppress the action of NO most likely through direct interaction between them, leading to the reduction of endogenous NO levels. These results provide insights into NO signaling and regulation of its bioactivity in plants.

The resurrection genome of Boea hygrometrica: A blueprint for survival of dehydration

Significance The genome analysis presented here represents a major step forward in the field of desiccation tolerance and a much-anticipated resource that will have a far-reaching effect in many areas of plant biology and agriculture. We present the ∼1.69-Gb draft genome of Boea hygrometrica, an important plant model for understanding responses to dehydration. To our knowledge, this is the first genome sequence of a desiccation-tolerant extremophile, offering insight into the evolution of this important trait and a first look, to our knowledge, into the genome organization of desiccation tolerance. The underpinning genome architecture and response in relation to the hydration state of the plant and its role in the preservation of cellular integrity has important implications for developing drought tolerance improvement strategies for our crops. “Drying without dying” is an essential trait in land plant evolution. Unraveling how a unique group of angiosperms, the Resurrection Plants, survive desiccation of their leaves and roots has been hampered by the lack of a foundational genome perspective. Here we report the ∼1,691-Mb sequenced genome of Boea hygrometrica, an important resurrection plant model. The sequence revealed evidence for two historical genome-wide duplication events, a compliment of 49,374 protein-coding genes, 29.15% of which are unique (orphan) to Boea and 20% of which (9,888) significantly respond to desiccation at the transcript level. Expansion of early light-inducible protein (ELIP) and 5S rRNA genes highlights the importance of the protection of the photosynthetic apparatus during drying and the rapid resumption of protein synthesis in the resurrection capability of Boea. Transcriptome analysis reveals extensive alternative splicing of transcripts and a focus on cellular protection strategies. The lack of desiccation tolerance-specific genome organizational features suggests the resurrection phenotype evolved mainly by an alteration in the control of dehydration response genes.

Nitric oxide negatively regulates AKT1-mediated potassium uptake through modulating vitamin B6 homeostasis in Arabidopsis

Significance Nitric oxide (NO) plays key roles in coordinating plant growth and development with environmental cues. Potassium (K+) is an essential plant nutrient important for growth and stress tolerance. However, little is known about the molecular connection of NO to K+ homeostasis. Through a genetic approach, this study provides a detailed regulatory mechanism of NO to K+ channel AKT1-mediated K+ absorption, through its modulation on vitamin B6 biosynthesis in plants. This finding demonstrates a previously unidentified role of NO in the control of K+ content in plants, which may represent a normal plant adaptive response under unfavorable external conditions. Nitric oxide (NO), an active signaling molecule in plants, is involved in numerous physiological processes and adaptive responses to environmental stresses. Under high-salt conditions, plants accumulate NO quickly, and reorganize Na+ and K+ contents. However, the molecular connection between NO and ion homeostasis is largely unknown. Here, we report that NO lowers K+ channel AKT1-mediated plant K+ uptake by modulating vitamin B6 biosynthesis. In a screen for Arabidopsis NO-hypersensitive mutants, we isolated sno1 (sensitive to nitric oxide 1), which is allelic to the previously noted mutant sos4 (salt overly sensitive 4) that has impaired Na+ and K+ contents and overproduces pyridoxal 5′-phosphate (PLP), an active form of vitamin B6. We showed that NO increased PLP and decreased K+ levels in plant. NO induced SNO1 gene expression and enzyme activity, indicating that NO-triggered PLP accumulation mainly occurs through SNO1-mediated vitamin B6 salvage biosynthetic pathway. Furthermore, we demonstrated that PLP significantly repressed the activity of K+ channel AKT1 in the Xenopus oocyte system and Arabidopsis root protoplasts. Together, our results suggest that NO decreases K+ absorption by promoting the synthesis of vitamin B6 PLP, which further represses the activity of K+ channel AKT1 in Arabidopsis. These findings reveal a previously unidentified pivotal role of NO in modulating the homeostasis of vitamin B6 and potassium nutrition in plants, and shed light on the mechanism of NO in plant acclimation to environmental changes.

Arabidopsis cryptochrome 1 functions in nitrogen regulation of flowering

Significance Overapplication of nitrogen (N) fertilizer causes delayed flowering and negatively impacts the function and composition of natural ecosystems and climate. In this study, we demonstrate that flowering time variations regulated by altered nitrogen levels are mediated by two key factors: ferredoxin-NADP+-oxidoreductase (FNR1) and the blue-light receptor cryptochrome 1 (CRY1). Nitrogen regulates FNR1 expression, thereby contributing to changes in NADPH/NADP+ and ATP/AMP ratios, which in turn activates adenosine monophosphate-activated protein kinase to modulate nuclear CRY1 abundance, which further acts in the N signal input pathway to affect central clock function and flowering time. A better understanding of N-regulated floral transition will offer biotechnological solutions to improve sustainable agriculture. The phenomenon of delayed flowering after the application of nitrogen (N) fertilizer has long been known in agriculture, but the detailed molecular basis for this phenomenon is largely unclear. Here we used a modified method of suppression-subtractive hybridization to identify two key factors involved in N-regulated flowering time control in Arabidopsis thaliana, namely ferredoxin-NADP+-oxidoreductase and the blue-light receptor cryptochrome 1 (CRY1). The expression of both genes is induced by low N levels, and their loss-of-function mutants are insensitive to altered N concentration. Low-N conditions increase both NADPH/NADP+ and ATP/AMP ratios, which in turn affect adenosine monophosphate-activated protein kinase (AMPK) activity. Moreover, our results show that the AMPK activity and nuclear localization are rhythmic and inversely correlated with nuclear CRY1 protein abundance. Low-N conditions increase but high-N conditions decrease the expression of several key components of the central oscillator (e.g., CCA1, LHY, and TOC1) and the flowering output genes (e.g., GI and CO). Taken together, our results suggest that N signaling functions as a modulator of nuclear CRY1 protein abundance, as well as the input signal for the central circadian clock to interfere with the normal flowering process.

Nitric oxide induces cotyledon senescence involving co-operation of the NES1/MAD1 and EIN2-associated ORE1 signalling pathways in Arabidopsis

Summary The NES1/MAD1 gene acts antagonistically with the EIN2-associated ORE1 signalling pathway to modulate the nitric oxide-induced Arabidopsis cotyledon senescence

Identification and expression profile analysis of NUCLEAR FACTOR-Y families in Physcomitrella patens

NUCLEAR FACTOR Y transcription factors belong to a multimember family and consist of NF-YA/B/C subunits. Members of the NF-Y family have been reported to regulate physiological processes in plant. In this study, we identified and annotated two NF-YA, nine NF-B, and twelve NF-YC proteins in the genome of Physcomitrella patens. Analyses of conserved domains demonstrated that PpNF-YA/B/C shared the same conserved domains with their orthologous proteins in Arabidopsis, O. sativa and mouse. Expression profiles indicated that PpNF-Ys were widely expressed in different tissues and developmental stages of P. patens throughout protonema and gametophores. The majority of PpNF-Y genes were responsive to abiotic stress via either ABA-independent or -dependent pathways. Some of ABA-regulated PpNF-Y expression were mediated by ABI3. To our knowledge, this study was the first to evaluate NF-Y families in Physcomitrella patens, and provides a foundation to dissect the function of PpNF-Ys.

The phosphoproteome in regenerating protoplasts from Physcomitrella patens protonemata shows changes paralleling postembryonic development in higher plants

Summary During protoplast regeneration, proteins related to cell morphogenesis, organogenesis and development adjustment were phosphorylated in Physcomitrella patens. These proteins play important roles in regulating postembryonic development in higher plants.

Physcomitrella Patens Dehydrins (PpDHNA and PpDHNC) Confer Salinity and Drought Tolerance to Transgenic Arabidopsis Plants

Dehydrins (DHNs) as a member of late-embryogenesis-abundant (LEA) proteins are involved in plant abiotic stress tolerance. Two dehydrins PpDHNA and PpDHNC were previously characterized from the moss Physcomitrella patens, which has been suggested to be an ideal model plant to study stress tolerance due to its adaptability to extreme environment. In this study, functions of these two genes were analyzed by heterologous expressions in Arabidopsis. Phenotype analysis revealed that overexpressing PpDHN dehydrin lines had stronger stress resistance than wild type and empty-vector control lines. These stress tolerance mainly due to the up-regulation of stress-related genes expression and mitigation to oxidative damage. The transgenic plants showed strong scavenging ability of reactive oxygen species(ROS), which was attributed to the enhancing of the content of antioxidant enzymes like superoxide dismutase (SOD) and catalase (CAT). Further analysis showed that the contents of chlorophyll and proline tended to be the appropriate level (close to non-stress environment) and the malondialdehyde (MDA) were repressed in these transgenic plants after exposure to stress. All these results suggest the PpDHNA and PpDHNC played a crucial role in response to drought and salt stress.

Heterologous expression of two Physcomitrella patens group 3 late embryogenesis abundant protein (LEA3) genes confers salinity tolerance in arabidopsis

Salinity stress is a major limiting factor in agriculture and adversely affecting the whole plant. As a halophyte, the moss Physcomitrella patens, has been suggested to be an ideal model plant to study salinity tolerance and adaption. Two abiotic stress-responsive Group 3 Late Embryogenesis Abundant protein genes had been identified in P. patens and named as PpLEA3-1 and PpLEA3-2, respectively. Functions of these two genes were analyzed by heterologous expressions in Arabidopsis, driven either by their native P. patens promoters or by the 35S CaMV constitutive promoter. Phenotype analysis revealed that pLEA3::LEA3, pLEA3::LEA3::GFP and 35S::LEA3::GFP transgenic lines had stronger salinity resistance than that in the wild type and empty-vector control. Further analysis showed that the contents of proline and soluble sugar were increased and the malondialdehyde (MDA) were repressed in these transgenic plants after exposure to salinity stress. Our observations indicate that these two Group 3 PpLEA genes played a role in the adaption to salinity stress.

Dehydration-responsive features of Atrichum undulatum

Drought is an increasingly important limitation on plant productivity worldwide. Understanding the mechanisms of drought tolerance in plants can lead to new strategies for developing drought-tolerant crops. Many moss species are able to survive desiccation—a more severe state of dehydration than drought. Research into the mechanisms and evolution of desiccation tolerance in basal land plants is of particular significance to both biology and agriculture. In this study, we conducted morphological, cytological, and physiological analyses of gametophytes of the highly desiccation-tolerant bryophyte Atrichumundulatum (Hedw.) P. Beauv during dehydration and rehydration. Our results suggested that the mechanisms underlying the dehydration–recovery cycle in A. undulatum gametophytes include maintenance of membrane stability, cellular structure protection, prevention of reactive oxygen species (ROS) generation, elimination of ROS, protection against ROS-induced damage, and repair of ROS-induced damage. Our data also indicate that this dehydration–recovery cycle consists not only of the physical removal and addition of water, but also involves a highly organized series of cytological, physiological, and biochemical changes. These attributes are similar to those reported for other drought- and desiccation-tolerant plant species. Our findings provide major insights into the mechanisms of dehydration-tolerance in the moss A. undulatum.