Cloning and characterization of the

Sugars as photosynthates are well known as energy providers and as building blocks of various structural components of plant cells, tissues and organs. Additionally, as a part of various sugar signaling pathways, they interact with other cellular machinery and influence many important cellular decisions in plants. Sugar signaling is further reliant on the differential distribution of sugars throughout the plant system. The distribution of sugars from source to sink tissues or within organelles of plant cells is a highly regulated process facilitated by various sugar transporters located in plasma membranes and organelle membranes, respectively. Sugar distribution, as well as signaling, are impacted during unfavorable environments such as extreme temperatures, salt, nutrient scarcity, or drought. Here, we have discussed the mechanism of sugar transport via various types of sugar transporters as well as their differential response during environmental stress exposure. The functional involvement of sugar transporters in plant's abiotic stress tolerance is also discussed. Besides, we have also highlighted the challenges in engineering sugar transporter proteins as well as the undeciphered modules associated with sugar transporters in plants. Thus, this review provides a comprehensive discussion on the role and regulation of sugar transporters during abiotic stresses and enables us to target the candidate sugar transporter(s) for crop improvement to develop climate-resilient crops.

Sugar transporters and their molecular tradeoffs during abiotic stress responses in plants.

The importance of increasing photosynthetic efficiency for sustainable crop yield increases to feed the growing world population is well recognized. The natural genetic variation in leaf photosynthesis in crop plants is largely unexploited for increasing yield potential. The genus Oryza, including cultivated rice and wild relatives, offers tremendous genetic variability to explore photosynthetic differences and underlying biochemical, photochemical, and developmental traits. We quantified leaf photosynthesis and related physiological parameters for six cultivated and three wild rice genotypes, and identified photosynthetically efficient wild rice accessions. Fitting A/Ci curves and biochemical analyses showed that leaf photosynthesis in cultivated rice varieties IR 64 and Nipponbare was limited due to leaf nitrogen content, Rubisco activity, and electron transport rate compared with photosynthetically efficient wild rice accessions Oryza australiensis and Oryza latifolia. The selected wild rice accessions with high leaf photosynthesis per unit area had anatomical features such as larger mesophyll cells with more chloroplasts, fewer mesophyll cells between two adjacent veins, and higher mesophyll cell and chloroplast surface area exposed to intercellular space. Our results show the existence of desirable variations in Rubisco activity, electron transport rate, and leaf anatomical features that could be targeted for increasing the photosynthetic efficiency of cultivated rice varieties.

High photosynthesis rate in two wild rice species is driven by leaf anatomy mediating high Rubisco activity and electron transport rate

The Dopamine D2 Receptor Gene

The source-sink relationship determines the overall agronomic performance of rice. Cloning and characterizing key genes involved in the regulation of source and sink dynamics is imperative for improving rice yield. However, few source genes with potential application in rice have been identified. Glucan, Water-Dikinase 1 (GWD1) is an essential enzyme that plays a pivotal role in the first step of transitory starch degradation in source tissues. In the present study, we successfully generated gwd1 weak mutants by promoter editing using CRISPR/Cas9 system, and also leaf-dominant overexpression lines of GWD1 driven by Osl2 promoter. Analysis of the gwd1 plants indicated that promoter editing mediated down-regulation of GWD1 caused no observable effects on rice growth and development, but only mildly modified its grain transparency and seed germination. However, the transgenic pOsl2::GWD1 overexpression lines showed improvements in multiple key traits, including rice yield, grain shape, rice quality, seed germination and stress tolerance. Therefore, our study shows that GWD1 is not only involved in transitory starch degradation in source tissues, but also plays key roles in the seeds, which is a sink tissue. In conclusion, we find that GWD1 is an ideal biotechnological target with promising potential for the breeding of elite rice cultivars via genetic engineering.

Glucan, Water-Dikinase 1 (GWD1), an ideal biotechnological target for potential improving yield and quality in rice.

Source-sink relationships are key to overall crop performance. Detailed understanding of the factors that determine source-sink dynamics is imperative for the balance of biomass and grain yield in crop plants. We investigated the differences in source-sink relationships between a cultivated rice, Oryza sativa cv. Nipponbare, and a wild rice, Oryza australiensis, which show striking differences in biomass and grain yield. Oryza australiensis, which accumulates a higher biomass, not only showed higher photosynthesis per unit leaf area but also exported more sucrose from leaves compared with Nipponbare. However, grain features and sugar content suggested limited sucrose mobilization to grains in the wild rice due to vasculature and sucrose transporter functions. Low cell wall invertase activity and high sucrose synthase cleavage activity followed by higher expression of cellulose synthase genes in O. australiensis stem indicated that it utilized photosynthates preferentially for the synthesis of structural carbohydrates, resulting in high biomass. In contrast, source-sink relationships favored high grain yield in Nipponbare via accumulation of transitory starch in the stem, due to higher expression of starch biosynthetic genes, which is mobilized to panicles at the grain filling stage. Thus, vascular features, sucrose transport, and functions of sugar metabolic enzymes explained the differences in source-sink relationships between Nipponbare and O. australiensis.

Sucrose transport and metabolism control carbon partitioning between stem and grain in rice.

Ethanol is a widely used drug, excessive consumption of which could lead to medical conditions with diverse symptoms Ethanol abuse causes dysfunction of memory, attention, speech and locomotion across species Dopamine signaling plays an essential role in ethanol dependent behaviors in animals ranging from C elegans to humans We devised an ethanol dependent assay in which mutants in the dopamine autoreceptor, dop-2, displayed a unique sedative locomotory behavior causing the animals to move in circles while dragging the posterior half of their body Here, we identify the posterior dopaminergic sensory neuron as being essential to modulate this behavior We further demonstrate that in dop-2 mutants, ethanol exposure increases dopamine secretion and functions in a DVA interneuron dependent manner DVA releases the neuropeptide NLP-12 that is known to function through cholinergic motor neurons and affect movement Thus, DOP-2 modulates dopamine levels at the synapse and regulates alcohol induced movement through NLP-12

/pdf/increased-dopaminergic-neurotransmission-results-in-ethanol-524lw3aep4.pdf

Increased dopaminergic neurotransmission results in ethanol dependent sedative behaviors in Caenorhabditis elegans.

The perception of our surrounding environment is an amalgamation of stimuli detected by sensory neurons. In Caenorhabditis elegans, olfaction is an essential behavior that determines various behavioral functions such as locomotion, feeding and development. Sensory olfactory cues also initiate downstream neuroendocrine signaling that controls aging, learning, development and reproduction. Innate sensory preferences toward odors (food, pathogens) and reproductive pheromones are modulated by 11 pairs of amphid chemosensory neurons in the head region of C. elegans Amongst these sensory neurons, the ASI neuron has neuroendocrine functions and secretes neuropeptides, insulin-like peptide (DAF-28) and the TGF-β protein, DAF-7. Its expression levels are modulated by the presence of food (increased levels) and population density (decreased levels). A recent study has shown that EXP-1, an excitatory GABA receptor regulates DAF-7/TGF-β levels and participates in DAF-7/TGF-β-mediated behaviors such as aggregation and bordering. Here, we show that exp-1 mutants show defective responses toward AWC-sensed attractive odors in a non-autonomous manner through ASI neurons. Our dauer experiments reveal that in daf-7 mutants, ASI expressed EXP-1 and STR-2 (a G-protein-coupled receptor; GPCR) that partially maintained reproductive growth of animals. Further, studies suggest that neuronal connections between ASI and AWC neurons are allowed at least partially through ASI secreted DAF-7 or through alternate TGF- β pathway/s regulated by EXP-1 and STR-2. Together, our behavioral, genetic and imaging experiments propose that EXP-1 and STR-2 integrate food cues and allow the animals to display DAF-7/TGF-β neuroendocrine dependent or independent behavioral responses contributing to chemosensensory and developmental plasticity.

/pdf/dauer-formation-in-c-elegans-is-modulated-through-awc-and-3wqoe3jpd1.pdf

Dauer Formation in C. elegans Is Modulated through AWC and ASI-Dependent Chemosensation.

Ethanol is a widely used drug, excessive consumption of which could lead to medical conditions with diverse symptoms. Ethanol abuse causes disinhibition of memory, attention, speech and locomotion across species. Dopamine signaling plays an essential role in ethanol dependent behaviors in animals ranging from C. elegans to humans. We devised an ethanol dependent assay in which mutants in the dopamine autoreceptor, dop-2, displayed a unique sedative locomotory behavior causing the animals to move in circles while dragging the posterior half of their body. We identify the posterior dopaminergic sensory neuron as being essential to modulate this behavior. We further demonstrate that in dop-2 mutants, ethanol exposure increases dopamine secretion and results in enhanced function of the DVA interneuron. DVA releases the neuropeptide NLP-12 and leads to the excitation of cholinergic motor neurons that affect movement. Thus, DOP-2 modulates dopamine levels at the synapse and regulates alcohol induced movement through NLP-12.

https://www.biorxiv.org/content/biorxiv/early/2019/09/23/779405.full.pdf

Loss of dop-2 causes increased dopamine release and locomotory defects in the presence of ethanol

The source-sink relationship is key to overall crop performance. Detailed understanding of the factors that determine source-sink dynamics is imperative for the balance of biomass and grain yield in crop plants. We investigated the differences in the source-sink relationship between a cultivated rice Oryza sativa cv. Nipponbare and a wild rice Oryza australiensis that show striking differences in biomass and grain yield. Oryza australiensis, accumulating higher biomass, not only showed higher photosynthesis per unit leaf area but also exported more sucrose from leaves than Nipponbare. However, grain features and sugar levels suggested limited sucrose mobilization to the grains in the wild rice due to vasculature and sucrose transporter functions. Low cell wall invertase activity and high sucrose synthase cleavage activity followed by higher expression of cellulose synthase genes in Oryza australiensis stem utilized photosynthates preferentially for the synthesis of structural carbohydrates, resulting in high biomass. In contrast, the source-sink relationship favored high grain yield in Nipponbare via accumulation of transitory starch in the stem, due to higher expression of starch biosynthetic genes, which is mobilized to panicles at the grain filling stage. Thus, vascular features, sucrose transport, and functions of sugar metabolic enzymes explained the differences in the source-sink relationship between Nipponbare and Oryza australiensis. Highlight Vascular features, sucrose transport, and sugar metabolic enzyme activity contribute to the differential source-sink relationship between the selected cultivated and wild rice that differ in biomass and grain yield.

https://www.biorxiv.org/content/biorxiv/early/2021/01/21/2020.10.03.324889.full.pdf

Anuradha Singh

Papers

Sucrose transport and metabolism control carbon partitioning between stem and grain in rice.

Increased dopaminergic neurotransmission results in ethanol dependent sedative behaviors in Caenorhabditis elegans.

Dauer Formation in C. elegans Is Modulated through AWC and ASI-Dependent Chemosensation.

Loss of dop-2 causes increased dopamine release and locomotory defects in the presence of ethanol

Sucrose transport and metabolism control carbon partitioning between stem and grain in rice