Identification of differentially expressed genes in dormant (banjhi) bud of tea (Camellia sinensis (L.) O. Kuntze) using subtractive hybridization approach

Genome-wide identification and immune response analysis of mitogen-activated protein kinase cascades in tea geometrid, Ectropis grisescens Warren (Geometridae, Lepidoptera)

BACKGROUND

Tea geometrid Ectropis grisescens (Geometridae: Lepidoptera), is one of the most destructive defoliators in tea plantations in China. The MAPK cascade is known to be an evolutionarily conserved signaling module, acting as pivotal cores of host-pathogen interactions. Although the chromosome-level reference genome of E. grisescens was published, the whole MAPK cascade gene family has not been fully identified yet, especially the expression patterns of MAPK cascade gene family members upon an ecological biopesticide, Metarhizium anisopliae, remains to be understood.

RESULTS

In this study, we have identified 19 MAPK cascade gene family members in E. grisescens, including 5 MAPKs, 4 MAP2Ks, 8 MAP3Ks, and 2 MAP4Ks. The molecular evolution characteristics of the whole Eg-MAPK cascade gene family, including gene structures, protein structural organization, chromosomal localization, orthologs construction and gene duplication, were systematically investigated. Our results showed that the members of Eg-MAPK cascade gene family were unevenly distributed in 13 chromosomes, and the clustered members in each group shared similar structures of the genes and proteins. Gene expression data revealed that MAPK cascade genes were expressed in all four developmental stages of E. grisescens and were fairly and evenly distributed in four different larva tissues. Importantly, most of the MAPK cascade genes were induced or constitutively expressed upon M. anisopliae infection.

CONCLUSIONS

In summary, the present study was one of few studies on MAPK cascade gene in E. grisescens. The characterization and expression profiles of Eg-MAPK cascades genes might help develop new ecofriendly biological insecticides to protect tea trees.

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.

Differential expression of gibberellin- and abscisic acid-related genes implies their roles in the bud activity-dormancy transition of tea plants

Thirty genes involved in GA and ABA metabolism and signalling were identified, and the expression profiles indicated that they play crucial roles in the bud activity-dormancy transition in tea plants. Gibberellin (GA) and abscisic acid (ABA) are fundamental phytohormones that extensively regulate plant growth and development, especially bud dormancy and sprouting transition in perennial plants. However, there is little information on GA- and ABA-related genes and their expression profiles during the activity-dormancy transition in tea plants. In the present study, 30 genes involved in the metabolism and signalling pathways of GA and ABA were first identified, and their expression patterns in different tissues were assessed. Further evaluation of the expression patterns of selected genes in response to GA₃ and ABA application showed that CsGA3ox, CsGA20ox, CsGA2ox, CsZEP and CsNCED transcripts were differentially expressed after exogenous treatment. The expression profiles of the studied genes during winter dormancy and spring sprouting were investigated, and somewhat diverse expression patterns were found for GA- and ABA-related genes. This diversity was associated with the bud activity-dormancy cycle of tea plants. These results indicate that the genes involved in the metabolism and signalling of GA and ABA are important for regulating the bud activity-dormancy transition in tea plants.

The identification and evaluation of two different color variations of tea

BACKGROUND

The tea plant, Camellia sinensis (L.) O. Kuntz, is a perennial woody plant widely cultivated for the production of a popular non-alcoholic beverage. To rapidly identify and evaluate two different color tea varieties (yellowish and purplish), the main phenotypic traits and quality components were tested in the present study. The metabolic profiles of tea shoots and leaves were also analyzed using liquid chromatography-tandem mass spectrometry.

RESULTS

The yellowish variation had a higher active level with respect to metabolism of catechins, and the contents of luteolin and kaempferol 3-α-d-glucoside were much higher compared to in the other variations. However, the purplish variation had a low content of theanine and a high content of caffeine. The contents of quercetin and kaempferol 3-α-d-galactoside were highest in purplish leaves. Moreover, the yellowish variation had the highest total quality scores for green teas and black teas, whereas the purplish variation had the highest scores for oolong teas.

CONCLUSION

Both the yellowish variation and the purplish variation represent excellent breeding materials and are worthy of breeding as new tea cultivars. The yellowish variation is more suitable for making high-grade green teas or black teas, whereas the purplish variation is suitable for producing fine quality oolong teas. © 2016 Society of Chemical Industry.

Biotechnological advances in tea (Camellia sinensis [L.] O. Kuntze): a review

This article presents a comprehensive review on the success and limitations of biotechnological approaches aimed at genetic improvement of tea with a purpose to explore possibilities to address challenging areas. Tea is a woody perennial tree with a life span of more than 100 years. Conventional breeding of tea is slow and limited primarily to selection which leads to narrowing down of its genetic base. Harnessing the benefits of wild relatives has been negligible due to low cross-compatibility, genetic drag and undesirable alleles for low yield. Additionally, being a recalcitrant species, in vitro propagation of tea is constrained too. Nevertheless, maneuvering with tissue/cell culture techniques, a considerable success has been achieved in the area of micropropagation, somatic embryogenesis as well as genetic transformation. Besides, use of molecular markers, "expressomics" (transcriptomics, proteomics, metabolomics), map-based cloning towards construction of physical maps, generation of expressed sequenced tags (ESTs) have facilitated the identification of QTLs and discovery of genes associated with abiotic or biotic stress tolerance and agronomic traits. Furthermore, the complete genome (or at least gene space) sequence of tea is expected to be accessible in the near future which will strengthen combinational approaches for improvement of tea. This review presents a comprehensive account of the success and limitations of the biotechnological tools and techniques hitherto applied to tea and its wild relatives. Expectedly, this will form a basis for making further advances aimed at genetic improvement of tea in particular and of economically important woody perennials in general.

Cold Treatment Breaks Dormancy but Jeopardizes Flower Quality in Camellia japonica L

Camellia japonica L. is an evergreen shrub whose cultivars are of great ornamental value. In autumn, after flower bud differentiation, dormancy is initiated. As in many other spring flowering woody ornamentals, winter low temperatures promote dormancy release of both flower and vegetative buds. However, warm spells during late autumn and winter can lead to unfulfilled chilling requirements leading to erratic and delayed flowering. We hypothesized that storing plants at no light and low temperature could favor dormancy breaking and lead to early and synchronized flowering in response to forcing conditions in C. japonica 'Nuccio's Pearl'. Plants with fully developed floral primordia were stored at dark, 7°C, and RH > 90% for up to 8 weeks. To monitor endodormancy release during the storage, we evaluated the content of abscisic acid (ABA) in flower buds and the expression profiles of five putative genes related to dormancy and cold acclimation metabolism in leaves and flower buds. In addition, the expression of four anthocyanin biosynthesis pathway genes was profiled in flower buds to assess the effect of the treatment on flower pigment biosynthesis. At 0, 4, 6, and 8 weeks of cold treatment, 10 plants were transferred to the greenhouse and forced to flower. Forced plant flower qualities and growth were observed. The ABA content and the expression profiles of two dormancy-related genes (CjARP and CjDEH) suggested that dormancy breaking occurred after 6-8 weeks of cold treatment. Overall, plants treated for 6-8 weeks showed earlier vegetative sprouting, enhanced, and homogeneous flowering with reduced forcing time. Prolonged cold treatments also reduced flower size and longevity, anthocyanin content, and pigment biosynthesis-related gene transcripts. In conclusion, the cold treatment had a promotive effect on dormancy breaking but caused severe drawbacks on flower quality.

Molecular cloning and expression analysis of tea plant aquaporin (AQP) gene family

The role of aquaporin proteins (AQPs) has been extensively studied in plants. However, the information of AQPs in the tea plant (Camellia sinensis) is unclear. In this manuscript, we isolated 20 full-length AQP cDNAs from the tea plant, and these sequences were classified into five subfamilies. The genes in these subfamilies displayed differential expression profiles in the studied tissues. The CsAQP expression patterns correlated with flower development and opening (FDO) and bud endodormancy (BED). To better understand the short-term expression patterns of CsAQPs in response to abiotic stress, tea plants were treated with abscisic acid (ABA), cold, salt or drought. ABA treatment down-regulated the expression of various CsAQPs. Salt up-regulated the transcription of most CsAQP genes. Cold treatment resulted in a complicated transcriptional regulation pattern for various CsAQPs. The expression of CsAQPs, especially plasma membrane intrinsic proteins (CsPIPs) and tonoplast intrinsic proteins (CsTIPs), was induced by drought and remained relatively high after rehydration in leaves, whereas almost all the CsAQPs were repressed in roots. Our results highlighted the diversity of CsAQPs in the tea plant and demonstrated that the CsPIP and CsTIP genes play a vital role in the stress response as well as in FDO and BED. Furthermore, certain CsSIPs (small basic intrinsic proteins), CsNIPs (NOD26-like intrinsic proteins) and CsXIPs (X intrinsic proteins) may regulate BED and FDO.

Differential expression of microRNAs in dormant bud of tea [Camellia sinensis (L.) O. Kuntze]

Expression analysis of miRNAs and understanding their target genes function in dormant tea bud might be used to identify molecular network panel and novel approaches for modulating dormancy in tea. Tea [Camellia sinensis (L) O. Kuntze, Theaceae] is an important commercial beverage crop manufactured from the apical bud and two leaves immediately below the bud. The yield and quality of tea depend on the vegetative growth of shoots and bud dormancy. The dormancy of bud is being regulated by many factors, such as mechanical, environmental and molecular mechanisms. MicroRNAs (miRNAs) are a newly identified class of small non-protein coding regulatory RNAs in both plants and animals which regulates gene expression at post-transcriptional level either by cleavage or translational inhibition of targeted mRNA transcripts. With these importances, the expression pattern of tea miRNAs was analyzed in active and dormant bud using stem-loop pulse RT-qPCR method. The results demonstrated the following expression pattern for highly up-regulated miRNAs, cs-miR 414[csmiR 408[cs-miR782[cs-miR169, and down-regulated miRNAs, cs-miR828[cs-miR1864[cs-miR852[csmiR1425 in dormant bud of tea. Furthermore, the role of target transcripts regulated by these miRNAs in relation to bud dormancy was discussed in detail. Therefore, the present study on the miRNA expression in tea will provide basis and considerably broaden the scope of understanding the function of miRNAs within the bud tissues and can serve as an initial point for RNA interference-based controlling strategies of bud dormancy in tea.

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.

Suppressive subtractive hybridization approach revealed differential expression of hypersensitive response and reactive oxygen species production genes in tea (Camellia sinensis (L.) O. Kuntze) leaves during Pestalotiopsis thea infection

Tea (Camellia sinensis (L.) O. Kuntze) is an economically important plant cultivated for its leaves. Infection of Pestalotiopsis theae in leaves causes gray blight disease and enormous loss to the tea industry. We used suppressive subtractive hybridization (SSH) technique to unravel the differential gene expression pattern during gray blight disease development in tea. Complementary DNA from P. theae-infected and uninfected leaves of disease tolerant cultivar UPASI-10 was used as tester and driver populations respectively. Subtraction efficiency was confirmed by comparing abundance of β-actin gene. A total of 377 and 720 clones with insert size >250 bp from forward and reverse library respectively were sequenced and analyzed. Basic Local Alignment Search Tool analysis revealed 17 sequences in forward SSH library have high degree of similarity with disease and hypersensitive response related genes and 20 sequences with hypothetical proteins while in reverse SSH library, 23 sequences have high degree of similarity with disease and stress response-related genes and 15 sequences with hypothetical proteins. Functional analysis indicated unknown (61 and 59 %) or hypothetical functions (23 and 18 %) for most of the differentially regulated genes in forward and reverse SSH library, respectively, while others have important role in different cellular activities. Majority of the upregulated genes are related to hypersensitive response and reactive oxygen species production. Based on these expressed sequence tag data, putative role of differentially expressed genes were discussed in relation to disease. We also demonstrated the efficiency of SSH as a tool in enriching gray blight disease related up- and downregulated genes in tea. The present study revealed that many genes related to disease resistance were suppressed during P. theae infection and enhancing these genes by the application of inducers may impart better disease tolerance to the plants.

Identification of differentially expressed genes in a spontaneous altered leaf shape mutant of the navel orange [Citrus sinensis (L.) Osbeck]

Most of the economically important citrus cultivars have originated from bud mutations. Leaf shape and structure are important factors that impact plant photosynthesis. We found a spontaneous bud mutant exhibiting a narrow leaf phenotype in navel orange [Citrus sinensis (L.) Osbeck]. To identify and characterize the genes involved in the formation of this trait, we performed suppression subtractive hybridization (SSH) and macroarray analysis. A total of 221 non-redundant differentially expressed transcripts were obtained. These transcripts included cell wall- and microtubule-related genes and two transcription factor-encoding genes, yabby and wox, which are crucial for leaf morphogenesis. Many highly redundant transcripts were associated with stress responses, while others, encoding caffeic acid 3-O-methyltransferase (EC 2.1.1.68) and a myb-like transcription factor, might be involved in the lignin pathway, which produces a component of secondary walls. Furthermore, real-time quantitative RT-PCR was performed for selected genes to validate the quality of the expressed sequence tags (ESTs) from the SSH libraries. This study represents an attempt to investigate the molecular mechanism associated with a leaf shape mutation, and its results provide new clues for understanding leaf shape mutations in citrus.