Prashant Mohanpuria

Expression of tea cytosolic glutamine synthetase is tissue specific and induced by cadmium and salt stress

Glutamine synthetase (GS) showed highest expression and activity in bud (youngest topmost leaf) of Camellia sinensis, lower in older leaves, while lowest activity in stem and roots. GS expression and activity was increased by ammonium and nitrate and also by cadmium and salt stress but decreased by copper, aluminum, drought, cold and heat stress.

Responses of Camellia sinensis cultivars to Cu and Al stress

The response of Camellia sinensis (L.) O. Kuntze cultivars Chinary and Assamica to Cu and Al stresses was investigated. Exposure to 100 µM CuSO4 or 100 µM AlCl3 led to accumulation of reactive oxygen species (ROS) more in Assamica than in Chinary. Proline content was higher in Chinary compared to Assamica, while chlorophyll and protein contents decreased upon Cu and Al exposure in both the cultivars. Expression of glutathione biosynthetic enzymes γ-glutamylcysteinyl synthetase (γ-ECS) and glutathione synthetase (GSHS) was elevated. Phytochelatin synthase (PCS), an enzyme involved in phytochelatins synthesis by using glutathione as a substrate was up-regulated at its transcript level more in Chinary than in Assamica. These results suggest that Chinary could be more tolerant than Assamica.

Producing low-caffeine tea through post-transcriptional silencing of caffeine synthase mRNA

In this study, attempt has been made to produce a selected cultivar of tea with low-caffeine content using RNAi technology. The caffeine biosynthetic pathway in tea has been proposed to involve three N-methyltransferases such as xanthosine methyltransferase, 7-N-methylxanthine methyltransferase and 3, 7-dimethylxanthine methyltransferase. Last two steps of caffeine biosynthesis in tea have been known to be catalyzed by a bifunctional enzyme known as caffeine synthase. To suppress the caffeine synthesis in the selected tea [Camellia sinensis (L.) O. Kuntze] cv. Kangra jat, we isolated a partial fragment of caffeine synthase (CS) from the same cultivar and used to design RNAi construct (pFGC1008-CS). Somatic embryos were transformed with the developed construct using biolistic method. Transformed somatic embryos showed reduction in the levels of CS transcript expression as well as in caffeine content. Plants were regenerated from the transformed somatic embryos. Transgenic plants showed a significant suppression of CS transcript expression and also showed a reduction of 44–61% in caffeine and 46–67% in theobromine contents as compared to the controls. These results suggest that the RNAi construct developed here using a single partial fragment of CS gene reduced the expression of the targeted endogenous gene significantly. However, the reduction in theobromine content in addition to caffeine documented the involvement of this single CS in the catalysis of last two methyl transfer steps in caffeine biosynthesis of tea.

Characterization of novel small RNAs from tea (Camellia sinensis L.)

Small RNAs play important roles in plant development, metabolism, signal transduction and responses to biotic and abiotic stresses by affecting gene expression. Tea (Camellia sinensis L.) is an important commercial crop in the world. To understand the regulatory mechanisms involving small RNAs in tea metabolism, we constructed a small RNA (sRNA) library from its tea drink manufacturing tissue part i.e. topmost two leaves and a bud. For the first time, we isolated and cloned six novel small RNAs candidates from tea. These were predicted to target 67 genes responsible for various important plant functions. Isolated small RNAs were validated through expression analysis in young leaf and old leaf during non-dormant and dormant growth phases of tea. Results suggest the probable role of isolated small RNAs in development and seasonal variations of tea.

Caffeine Biosynthesis and Degradation in Tea [Camellia sinensis (L.) O. Kuntze] is under Developmental and Seasonal Regulation

To study caffeine biosynthesis and degradation, here we monitored caffeine synthase gene expression and caffeine and allantoin content in various tissues of four Camellia sinensis (L.) O. Kuntze cultivars during non-dormant (ND) and dormant (D) growth phases. Caffeine synthase expression as well as caffeine content was found to be higher in commercially utilized tissues like apical bud, 1st leaf, 2nd leaf, young stem, and was lower in old leaf during ND compared to D growth phase. Among fruit parts, fruit coats have higher caffeine synthase expression, caffeine content, and allantoin content. On contrary, allantoin content was found lower in the commercially utilized tissues and higher in old leaf. Results suggested that caffeine synthesis and degradation in tea appears to be under developmental and seasonal regulation.

Transient RNAi based gene silencing of glutathione synthetase reduces glutathione content in Camellia sinensis (L.) O. Kuntze somatic embryos

We report on gene silencing of glutathione synthetase (GSHS) that reduces reduced glutathione (GSH) content in somatic embryos of Camellia sinensis L. Using degenerate primers with cDNA of Camellia sinensis, a 457 bp GSHS gene fragment was cloned through polymerase chain reaction. This fragment was used in making ihpRNA. For this it was cloned in sense at AscI and SwaI and in anti-sense at Bam HI and XbaI restriction sites of pFGC5941 that has chalcone synthase (Chs) intron between SwaI and BamHI restriction sites. Resultant RNAi construct was used for C. sinensis somatic embryos transformation through Agrobacterium. After 11, 13 and 15 d of transformation, embryo GSHS transcript levels and GSH content decreased to a great extent which documented the feasibility of RNAi based gene silencing in C. sinensis.

A CsGS is regulated at transcriptional level during developmental stages and nitrogen utilization in Camellia sinensis (L.) O. Kuntze

Glutamine synthetase is a very important enzyme of ammonium assimilation in plants. Here, we report on the regulation of a cytosolic glutamine synthetase (CsGS) from Camellia sinensis (L.) O. Kuntze during developmental stages and light/dark conditions on the utilization of nitrate and ammonia. The CsGS expression levels decreased during dormancy compared to non-dormancy phase of growth. Different leaf positions present different ages of the leaf and CsGS expression level was highest in apical bud (youngest leaf) and lower in mature fourth leaf, suggesting transcriptional regulation of CsGS during developmental stages. The CsGS enzyme activity showed similar trend to that of expression during developmental stages. The nitrate, ammonium and total amino acid contents were increased upon exposure to both N-sources during light and dark conditions. During light conditions, expression of CsGS in apical bud increased upon exposure to both N-sources nitrate and ammonium. While during dark conditions expression was increased only by ammonium and nitrate had no influence. Exposure to both N-sources also showed enhancing effect on CsGS enzyme activity during light. Under dark, ammonium application increased CsGS enzyme activity and nitrate had inhibitory effect on the activity. Results suggest the transcriptional regulation of CsGS on N-utilization during light/dark conditions.

Osmotin-expressing transgenic tea plants have improved stress tolerance and are of higher quality

Drought is a major stress that affects the yield and quality of tea, a widely consumed beverage crop grown in more than 20 countries of the world. Therefore, osmotin gene-expressing transgenic tea plants produced using earlier optimized conditions were evaluated for their tolerance of drought stress and their quality. Improved tolerance of polyethylene glycol-induced water stress and faster recovery from stress were evident in transgenic lines compared with the normal phenotype. Significant improvements in growth under in-vitro conditions were also observed. Besides enhanced reactive oxygen species-scavenging enzyme activity, the transgenic lines contained significantly higher levels of flavan-3-ols and caffeine, key compounds that govern quality and commercial yield of the beverage. The selected transgenic lines have the potential to meet the demands of the tea industry for stress-tolerant plants with higher yield and quality. These traits of the transgenic lines can be effectively maintained for generations because tea is commercially cultivated through vegetative propagation only.