Synergistic effect of cytokinin and gibberellins stimulates release of dormancy in tea (Camellia sinensis (L.) O. Kuntze) bud.

Reactivation of dormant meristem in banjhi (dormant) shoots is important to enhance the quality and quantity of tea production. The field grown tea bushes were subjected to treatment with dormancy breaking agents such as potassium nitrate (KNO3), thiourea, sodium nitro prusside (SNP), the phytohormones kinetin (Kn) and gibberellins (GA). The efficacy of Kn and GA were comparatively lesser than KNO3 while the combination of Kn and GA (50 and100 ppm respectively) resulted in better dormancy reduction in tea buds. This observation was supported by our results from gene expression study where accumulation patterns of mRNAs corresponding to histones (H2A, H2B, H3 and H4), cyclins (B2, D1 and D3), cyclin-dependent kinase (CDKA), ubiquitination enzymes (FUS, EXT CE2), cyclophilin, E2F, and tubulin were analyzed during growth-dormancy cycles in tea apical buds under the influence of Kn, GA and their combinations. The level of these mRNAs was low in dormant buds, which was significantly increased by foliar application of GA and Kn combination. The present study indicated that the foliar application of GA in combination with Kn will help to improve quality and quantity of tea production by breaking dormancy and stimulating the bud growth.

Biochemical and molecular studies on the resistance mechanisms in tea [Camellia sinensis (L.) O. Kuntze] against blister blight disease.

Tea (Camellia sinensis) plantations are exposed to biotic and abiotic stresses. Among the biotic factors, blister blight (BB), caused by Exobasidium vexans, affects the quality and quantity of the product and demands high fungicide application. A long term solution for disease resistance would require the knowledge of the basic molecular and biochemical changes occurring in plant as an attempt to resist the pathogen and limit the spread of the disease which can further help in developing resistant cultivars using biotechnological tools. Thus, gene expression studies using the cDNA based suppressive subtractive hybridization library, characterization of genes for pathogenesis related (PR) proteins [chitinase (CsCHIT), glucanase (CsGLUC), phenylalanine ammonia lyase (CsPAL)] and genes in flavonoid pathway were accessed in the BB resistant and susceptible cultivars, SA6 and TES34, respectively. Further, biochemical analysis of PR and antioxidant enzymes (POX, APX, SOD) involved in BB resistance have been carried out to investigate the potential molecular and biochemical changes. Various stages of pathogen development had varied impact on PR protein, flavonoid pathway and anti-oxidative enzymes and indicates the possible role of reactive oxygen species, lignins, flavonoids, anthocyanins and other synthesized compounds in acting as antimicrobial/antifungal agents in tea cultivars.

Identification and validation of sugarcane streak mosaic virus-encoded microRNAs and their targets in sugarcane.

Plants have developed several defense mechanisms to cope with various pathogens (bacteria, fungi, virus, and phytoplasma). Among these, RNA interference (RNAi)-mediated defense against viral infection was found to be a major innate immune response. As a counter attack strategy against the host defense, viruses produce suppressors of host RNAi pathway. MicroRNAs (miRNAs) are an abundant class of short (~18-22 nucleotide) non-coding single-stranded RNAs involved in RNAi pathway leading to post-transcriptional regulation of gene expression. Sugarcane streak mosaic virus (SCSMV) is a distinct strain of Potyviridae family which has a single-stranded positive-sense RNA genome causing mosaic disease in sugarcane. In this study, we computationally predicted and experimentally validated the miRNA encoded by the SCSMV genome with detection efficiency of 99.9 % in stem-loop RT-qPCR and predicted their potential gene targets in sugarcane. These sugarcane target genes considerably broaden future investigation of the SCSMV-encoded miRNA function during viral pathogenesis and might be applied as a new strategy for controlling mosaic disease in sugarcane.

Analysis of dormant bud (Banjhi) specific transcriptome of tea (Camellia sinensis (L.) O. Kuntze) from cDNA library revealed dormancy-related genes.

Bud dormancy is of ecological and economical interest due to its impact on tea (Camellia sinensis (L.) O. Kuntze) plant growth and yield. Growth regulation associated with dormancy is an essential element in plant's life cycle that leads to changes in expression of large number of genes. In order to identify and provide a picture of the transcriptome profile, cDNA library was constructed from dormant bud (banjhi) of tea. Sequence and gene ontology analysis of 3,500 clones, in many cases, enabled their functional categorization concerning the bud growth. Based on the cDNA library data, the putative role of identified genes from tea is discussed in relation to growth and dormancy, which includes morphogenesis, cellular differentiation, tropism, cell cycle, signaling, and various metabolic pathways. There was a higher representation of unknown processes such as unknown molecular functions (65.80 %), unknown biological processes (62.46 %), and unknown cellular components (67.42 %). However, these unknown transcripts represented a novel component of transcripts in tea plant bud growth and/or dormancy development. The identified transcripts and expressed sequence tags provides a valuable public resource and preliminary insights into the molecular mechanisms of bud dormancy regulation. Further, the findings will be the target of future expression experiments, particularly for further identification of dormancy-related genes in this species.

Structural and docking studies of a nucleoside diphosphate kinase 1 (CsNDPK1) from tea [Camellia sinensis (L.) O. Kuntze].

Nucleoside diphosphate kinase (NDPK, EC 2.7.4.6) is a housekeeping gene, which functions in the general homeostasis of cellular nucleoside triphosphate (NTP) pools. Among the various NDPK isoforms, cytosolic NDPK1 has been shown to be the main NDPK isoform in plants, accounting for more than 70 % of total NDPK activity in plants. For the first time, a full-length cDNA (697 bp), designated as CsNDPK1 was cloned from tea leaves and consisted of a 448-bp open reading frame (ORF) encoding a 147-amino-acid polypeptide with calculated molecular mass of 16.1 kDa and a pI of 6.3. Homology modeling of CsNDPK1 shows that the presented tea NDPK1 also contains several motifs, binding and catalytic sites which are highly conserved among other NDPKs. Docking studies of CsNDPK1 with its substrates (NTPs) are discussed in detail. In summary, we describe a reliable model of CsNDPK1 that can be used in structure-based protein-protein interaction studies for identifying its potential role in intracellular communication and its physiological significance in tea.

Functional characterization of sugarcane MYB transcription factor gene promoter (PScMYBAS1) in response to abiotic stresses and hormones.

The sugarcane (Saccharum officinarum) stress-related MYB transcription factor gene, ScMYBAS1, demonstrated induced response to water deficit and salt stress in our previous study. To elucidate its stress tolerance mechanism at the transcriptional level, we isolated and characterized the promoter (PScMYBAS1, 1,033 bp) flanking the 5' ScMYBAS1 coding region from the sugarcane genome. A series of PScMYBAS1 deletion derivatives from the transcription start site (-56, -152, -303, -442, -613, -777, -843, -1,033) was fused to the uidA reporter gene (GUS) and each deletion construct was analyzed by Agrobacterium-mediated transient transformation in tobacco leaves subjected to dehydration, salinity, cold, wounding, gibberellic acid (GA), salicylic acid (SA), and methyl jasmonic acid (MeJA). Deletion analysis of the promoter, PScMYBAS1, suggested that the 303-bp promoter region was required for basal expression. Promoter fragments, 777 bp or longer showed ~twofold to ~fourfold increased induction of GUS in response to abiotic stress (dehydration, salt, cold, wounding) and hormone (SA, MeJA) treatments. These findings further our understanding of the regulation of ScMYBAS1 expression and provide a new stress-inducible promoter system in transgenic plants.