Molecular basis of flavonoid accumulation in tea leaves grafted with Camellia sinensis var. assamica cv. “Yinghong9” as rootstock based on multi-omics analysis

C. sinensis is an economically important crop for tea production that experiences increasing demand and good export potential. Therefore, crops need to be expanded, and high-quality planting material is required. Vegetative propagation by cuttings is the prevalent method; therefore, this paper explored its optimization potential modeled on cultivar ‘Jiukengzao’. This study wanted to deeply explore blue-light-induced adventitious root formation and development of tea cuttings, so we conducted short-term (0 h, 8 h, and 16 h) and long-term (30 d, 60 d, and 90 d) time-course analyses on tea cutting seedlings. Short-term, full-length transcriptome analysis showed that the expression of genes related to plant hormone signal transduction and auxin transport was highest at 16 h. Sixteen hours of light was considered as suitable for adventitious root growth and development of tea cuttings. Long-term phytohormone analysis showed that the trend of indole-3-carboxylic acid (ICA) change was: 60 d > 90 d > 30 d. Long-term, full-length transcriptome analysis showed that the gene expression trends in K2, K5, K6, and K8 clusters were: 90 d > 60 d > 30 d, and the opposite was observed in K1, K4, and K11 clusters. Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis showed that most of the genes in these seven clusters are involved in “plant hormone signal transduction (ko04075)”. This includes auxin early responsive protein AUX/IAA, auxin response factor ARF, auxin-responsive protein SAUR, etc. In addition, genes related to auxin transport and synthesis were identified as PIN1, 3, 4, PILS2, 6, 7, flavin-containing monooxygenase YUC9, and YUC10, and the expression trend of these genes was mostly consistent with the change trend of ICA content. This study further explained the molecular mechanism of blue-light-induced adventitious root formation and development of tea cuttings. It is recommended that blue light can be used to promote the adventitious root growth and development of tea cuttings in practical production.

Time-Course Transcriptome and Phytohormonal Analysis of Blue-Light-Induced Adventitious Root Development of Tea Cuttings (Camellia sinensis (L.) Kuntze)

The occurrence of adventitious roots and somatic embryos is a crucial step in micropropagation that frequently limits the application of this technique in woody plants. Recent studies demonstrated that they can be negatively or positively regulated with γ-aminobutyric acid (GABA), which is a four-carbon non-proteinous amino acid that not only acts as a main inhibitory neurotransmitter in mammals. It has been reported that GABA affects plant growth and their response to stress although its mode of action is still unclear. This review dealt with the effects of GABA on adventitious root formation and growth as well as on somatic embryogenesis. Furthermore, we focused on discussing the interaction of GABA with phytohormones, such as auxin, ethylene, abscisic acid, and gibberellin, as well as with the carbon and nitrogen metabolism during adventitious root development. We suggested that research on GABA will contribute to the application of micropropagation in the recalcitrant fruit and forest species.

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The Role of γ-Aminobutyric Acid (GABA) in the Occurrence of Adventitious Roots and Somatic Embryos in Woody Plants

Both arbuscular mycorrhizal fungi (AMF) and phytohormones collectively regulate plant growth and root development, but their individual and combined effects on tea [Camellia sinensis (L.) O. Kuntze] cutting seedings remain unclear. This study examined the individual and combined effects of two species of AMF (Rhizophagus intraradices, RI and Funneliformis mosseae, FM) and two types of palnt hormones (strigolactones, SLs; polyamines, PAs) on tea cutting seedings, by evaluating the growth and physiobiochemical characteristics of plants treated with the AMFs and/or hormones. The results showed that inoculation with either AMF individually or hormones treatment alone could significantly enhanced mycorrhizal colonization, growth target and physiobiochemical characteristics of tea cutting seedlings. Interestingly, the addition of a combination of AMFs and hormones showed superior effects, while SL and RI exhibited the most improvements to the colonization rate, plant growth, root-morphological traits, root DHA activity, photosynthesis, chlorophyll content, soluble sugar content in leaves, and the activities of antioxidant enzymes (SOD, POD, and CAT), compared to other treatment combinations (SL + FM, PA + RI, and PA + FM). Correlation analyses revealed a significantly (p < 0.05) positive correlation of root AMF colonization with root-related traits (e.g., DHA, root total length, surface area, and volume) and leaf-related traits (e.g., leaf area, shoot biomass, total chlorophyll, and antioxidant enzyme activities). This study demonstrated that while the apllication of individual AMF or plant hormones had a certain good effects on most growth and physiobiochemical characteristics parameters of tea cutting seedings, the additive effect was from specific combined of AMF and plant hormones. These results highlight the possibility for combined of AMF and plant hormones to improve the asexual reproduction of tea plants via cuttings.

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Individual and combined effects of arbuscular mycorrhizal fungi and phytohormones on the growth and physiobiochemical characteristics of tea cutting seedlings

Tea plant breeding or cultivation mainly involves propagation via cuttings, which not only ensures the inheritance of the excellent characteristics of the mother plant but also facilitates mechanized management. The formation of adventitious root (AR) determines the success of cutting-based propagation, and auxin is an essential factor involved in this process. To understand the molecular mechanism underlying AR formation in nodal tea cuttings, transcriptome and endogenous hormone analysis was performed on the stem bases of red (mature)- and green (immature)-stem cuttings of 'Echa 1 hao' tea plant as affected by a pulse treatment with naphthalene acetic acid (NAA).In this study, NAA significantly promoted AR formation in both red- and green-stem cuttings but slightly reduced callus formation. External application of NAA reduced the levels of endogenous indole-3-acetic acid (IAA) and cytokinin (TZR, trans-zeatin riboside). The number of DEGs (NAA vs. CK) identified in the green-stem cuttings was significantly higher than that in the red-stem cuttings, which corresponded to a higher rooting rate of green-stem cuttings under the NAA treatment. A total of 82 common DEGs were identified as being hormone-related and involved in the auxin, cytokinin, abscisic acid, ethylene, salicylic acid, brassinosteroid, and jasmonic acid pathways. The negative regulation of NAA-induced IAA and GH3 genes may explain the decrease of endogenous IAA. NAA reduced endogenous cytokinin levels and further downregulated the expression of cytokinin signalling-related genes. By the use of weighted gene co-expression network analysis (WGCNA), several hub genes, including three [cellulose synthase (CSLD2), SHAVEN3-like 1 (SVL1), SMALL AUXIN UP RNA (SAUR21)] that are highly related to root development in other crops, were identified that might play important roles in AR formation in tea cuttings.NAA promotes the formation of AR of tea cuttings in coordination with endogenous hormones. The most important endogenous AR inductor, IAA, was reduced in response to NAA. DEGs potentially involved in NAA-mediated AR formation of tea plant stem cuttings were identified via comparative transcriptome analysis. Several hub genes, such as CSLD2, SVL1 and SAUR21, were identified that might play important roles in AR formation in tea cuttings. 

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Integrated transcriptome and hormonal analysis of naphthalene acetic acid-induced adventitious root formation of tea cuttings (Camellia sinensis)

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Yinhong Qian

Papers

Integrated transcriptome and hormonal analysis of naphthalene acetic acid-induced adventitious root formation of tea cuttings (Camellia sinensis)

Integrated transcriptome and hormonal analysis of naphthalene acetic acid-induced adventitious root formation of tea cuttings (Camellia sinensis)