Isolation and functional characterization of Lycopene β-cyclase (CYC-B) promoter from Solanum habrochaites

<p>Abstract</p> <p>Background</p> <p>Carotenoids are a group of C40 isoprenoid molecules that play diverse biological and ecological roles in plants. Tomato is an important vegetable in human diet and provides the vitamin A precursor <it>β</it>-carotene. Genes encoding enzymes involved in carotenoid biosynthetic pathway have been cloned. However, regulation of genes involved in carotenoid biosynthetic pathway and accumulation of specific carotenoid in chromoplasts are not well understood. One of the approaches to understand regulation of carotenoid metabolism is to characterize the promoters of genes encoding proteins involved in carotenoid metabolism. <it>Lycopene β-cyclase </it>is one of the crucial enzymes in carotenoid biosynthesis pathway in plants. Its activity is required for synthesis of both α-and β-carotenes that are further converted into other carotenoids such as lutein, zeaxanthin, etc. This study describes the isolation and characterization of chromoplast-specific <it>Lycopene β-cyclase </it>(<it>CYC-B</it>) promoter from a green fruited <it>S. habrochaites </it>genotype EC520061.</p> <p>Results</p> <p>A 908 bp region upstream to the initiation codon of the <it>Lycopene β-cyclase </it>gene was cloned and identified as full-length promoter. To identify promoter region necessary for regulating developmental expression of the <it>ShCYC-B </it>gene, the full-length promoter and its three different 5' truncated fragments were cloned upstream to the initiation codon of <it>GUS </it>reporter cDNA in binary vectors. These four plant transformation vectors were separately transformed in to <it>Agrobacterium</it>. <it>Agrobacterium</it>-mediated transient and stable expression systems were used to study the <it>GUS </it>expression driven by the full-length promoter and its 5' deletion fragments in tomato. The full-length promoter showed a basal level activity in leaves, and its expression was upregulated > 5-fold in flowers and fruits in transgenic tomato plants. Deletion of -908 to -577 bp 5' to ATG decreases the <it>ShCYC-B </it>promoter strength, while deletion of -908 to -437 bp 5' to ATG led to significant increase in the activity of GUS in the transgenic plants. Promoter deletion analysis led to the identification of a short promoter region (-436 bp to ATG) that exhibited a higher promoter strength but similar developmental expression pattern as compared with the full-length <it>ShCYC-B </it>promoter.</p> <p>Conclusion</p> <p>Functional characterization of the full-length <it>ShCYC-B </it>promoter and its deletion fragments in transient expression system <it>in fruto </it>as well as in stable transgenic tomato revealed that the promoter is developmentally regulated and its expression is upregulated in chromoplast-rich flowers and fruits. Our study identified a short promoter region with functional activity and developmental expression pattern similar to that of the full-length <it>ShCYC-B </it>promoter. This 436 bp promoter region can be used in promoter::reporter fusion molecular genetic screens to identify mutants impaired in <it>CYC-B </it>expression, and thus can be a valuable tool in understanding carotenoid metabolism in tomato. Moreover, this short promoter region of <it>ShCYC-B </it>may be useful in genetic engineering of carotenoid content and other agronomic traits in tomato fruits.</p

Disentangling the roles of plant water status and stem carbohydrate remobilization on rice harvest index under drought

"Harvest index is an important component of grain yield and is typically reduced by reproductive stage drought stress in rice. Multiple drought response mechanisms can affect harvest index including plant water status and the degree of stem carbohydrate mobilization during grain filling. In this study, we aimed to dissect the contributions of plant water status and stem carbohydrate mobilization to harvest index. Pairs of genotypes selected for contrasting harvest index but similar biomass and days to flowering were characterized at ICAR-RCER, Patna, India and at IRRI, Philippines. Multiple traits were related with harvest index across experiments, including mobilization efficiency at both sites as indicated by groupings in principal component analysis, and plant water status as indicated by direct correlations. Biomass-related traits were positively correlated with harvest index at IRRI but biomass was negatively correlated with harvest index at ICER-RCER, Patna. We observed that some pairs of genotypes showed differences in harvest index across environments, whereas other showed differences in harvest index only under drought. Of all time points measured when all genotypes were considered together, the stem carbohydrate levels at maturity were most consistently (negatively) correlated with harvest index under drought, but not under well-watered conditions. However, in the pairs of genotypes grouped as those whose differences in harvest index were stable across environments, improved plant water status resulted in a greater ability to both accumulate and remobilize stored carbohydrate, i.e. starch. Conclusion By distinguishing between genotypes whose harvest index was improved across conditions as opposed to specifically under drought, we can attribute the mechanisms behind the stable high-harvest index genotypes to be more related to stem carbohydrate remobilization than to plant water status. The stable high-harvest index lines in this study (Aus 257 and Wanni Dahanala) may confer mechanisms to improve harvest index that are independent of drought response and therefore may be useful for breeding improved rice varieties.

Physiochemical response of papaya genotypes exposed to low temperature regimes

Susceptibility to low temperature stress is the major threat to papaya cultivation. Here, we studied a low temperature stress tolerance in papaya plant. We have investigated the effect of different low temperature regimes, 28°/18°C (day/night) to 16°/06°C (day/night) with a gradual decrease of 2°C on every two days and one set with direct exposure to the low temperature of 18°/08°C (day/night), called the acclimatized plant, in five diverse papaya genotypes (Pusa Nanha, Red Lady P-7-2, P-7-9, and P-7-14) and cold tolerant wild relative of cultivated papaya genotype (Vasconcellea cundinamarcensis V.M. Badillo) under controlled regulated conditions. It was observed that there were significant variations in the physiological and biochemical parameters like photosynthetic gas exchange parameters, chlorophyll content, fluorescence parameters, relative water content (RWC), membrane stability index (MSI), total sugars content, total soluble proteins content, lipid peroxidation, and proline accumulation in leaf tissues. Maximum stomatal conductance, chlorophyll fluorescence, RWC, MSI, total sugars, total soluble proteins, proline and lowest MDA contents were observed in Vasconcellea cundinamarcensis followed by inbred P-7-9 as compared to other genotypes under low temperature stress. Among all the papaya genotypes, P-7-9 showed more adaptability to low temperature stress and it further give new insights for developing low temperature tolerant papaya genotypes, especially under changing climate situations

Root System Architecture and Omics Approaches for Belowground Abiotic Stress Tolerance in Plants

Plant growth and productivity is negatively affected by several abiotic stresses. To overcome the antagonistic effect of a changing environment, plants have evolved several modifications at the physiological as well as molecular levels. Besides being a vital organ for a plant&rsquo;s nutrient uptake, roots also plays a significant role in abiotic stress regulation. This review provides insight into changing Root System Architecture (RSA) under varying environmental stimuli using high-throughput omics technologies. Several next-generation and high-throughput omics technologies, such as phenomics, genomics, transcriptomics, proteomics, and metabolomics, will help in the analysis of the response of root architectural traits under climatic vagaries and their impact on crop yield. Various phenotypic technologies have been implied for the identification of diverse root traits in the field as well as laboratory conditions, such as root-box pinboards, rhizotrons, shovelomics, ground-penetrating radar, etc. These phenotypic analyses also help in identifying the genetic regulation of root-related traits in different crops. High-throughput genomic as well as transcriptome analysis has led researchers to unravel the role of the root system in response to these environmental cues, even at the single-cell level. Detailed analysis at the protein and metabolite levels can provide a better understanding of the response of roots under different abiotic stresses. These technologies will help in the improvement of crop productivity and development of resistant varieties