Transcriptome profiling of the fertile parent and sterile hybrid in tea plant flower buds

The MADS-box transcription factor CsAGL9 plays essential roles in seed setting in Camellia sinensis

The number of seed setting (NSS) is an important biological trait that affects tea propagation and yield. In this study, the NSS of an F1 tea population (n = 324) generated via a cross between 'Longjing 43' and 'Baihaozao' was investigated at two locations in two consecutive years. Quantitative trait locus (QTL) mapping of the NSS was performed, and 10 major QTLs were identified. In total, 318 genes were found in these 10 QTLs intervals, and 11 key candidate genes were preliminarily identified. Among them, the MADS-box transcription factor AGAMOUS LIKE 9 (CsAGL9, CSS0037962) located in the most stable QTL (qNSS2) was identified as a key gene affecting the NSS. CsAGL9 overexpression in Arabidopsis promoted early flowering and significantly decreased the length and number of pods and number of seeds per pod. Transcriptome analysis demonstrated that the auxin pathway, a key hormone pathway regulating plant reproduction, was highly affected in the transgenic lines. The auxin pathway was likewise the most prominent in the gene co-expression network study of CsAGL9 in tea plants. In summary, we identified CsAGL9 is essential for seed setting using QTL mapping integrated with RNA-seq, which shed a new light on the mechanism NSS of seed setting in tea plants.

Functional Analyses of Flavonol Synthase Genes From Camellia sinensis Reveal Their Roles in Anther Development

Flavonoids, including flavonol derivatives, are the main astringent compounds of tea and are beneficial to human health. Many researches have been conducted to comprehensively identify and characterize the phenolic compounds in the tea plant. However, the biological function of tea flavonoids is not yet understood, especially those accumulated in floral organs. In this study, the metabolic characteristics of phenolic compounds in different developmental stages of flower buds and various parts of the tea flower were investigated by using metabolomic and transcriptomic analyses. Targeted metabolomic analysis revealed varying accumulation patterns of different phenolic polyphenol compounds during flowering; moreover, the content of flavonol compounds gradually increased as the flowers opened. Petals and stamens were the main sites of flavone and flavonol accumulation. Compared with those of fertile flowers, the content of certain flavonols, such as kaempferol derivatives, in anthers of hybrid sterile flowers was significantly low. Transcriptomic analysis revealed different expression patterns of genes in the same gene family in tea flowers. The CsFLSb gene was significantly increased during flowering and was highly expressed in anthers. Compared with fertile flowers, CsFLSb was significantly downregulated in sterile flowers. Further functional verification of the three CsFLS genes indicated that CsFLSb caused an increase in flavonol content in transgenic tobacco flowers and that CsFLSa acted in leaves. Taken together, this study highlighted the metabolic properties of phenolic compounds in tea flowers and determined how the three CsFLS genes have different functions in the vegetative and reproductive organs of tea plants. Furthermore, CsFLSb could regulated flavonol biosynthesis in tea flowers, thus influencing fertility. This research is of great significance for balancing the reproductive growth and vegetative growth of tea plants.

Identification and characterization of miRNAs associated with sterile flower buds in the tea plant based on small RNA sequencing

Background

miRNAs are a type of conserved, small RNA molecule that regulate gene expression and play an important role in the growth and development of plants. miRNAs are involved in seed germination, root development, shoot apical meristem maintenance, leaf development, and flower development by regulating various target genes. However, the role of miRNAs in the mechanism of tea plant flower sterility remains unclear. Therefore, we performed miRNA sequencing on the flowers of fertile male parents, female parents, and sterile offspring.

Results

A total of 55 known miRNAs and 90 unknown miRNAs were identified. In the infertile progeny, 37 miRNAs were differentially expressed; 18 were up-regulated and 19 were down-regulated. miR156, miR157, miR164, miR167, miR169, miR2111 and miR396 family members were down-regulated, and miR160, miR172 and miR319 family members were up-regulated. Moreover, we predicted that the 37 differentially expressed miRNAs target a total of 363 genes, which were enriched in 31 biological functions. We predicted that miR156 targets 142 genes, including ATD1A, SPL, ACA1, ACA2, CKB22 and MADS2.

Conclusion

We detected a large number of differentially expressed miRNAs in the sterile tea plant flowers, and their target genes were involved in complex biological processes. Among these miRNAs, the down-regulation of miR156 may be one of the factor in the formation of sterile floral buds in tea plants.

Supplementary Information

The online version contains supplementary material available at 10.1186/s41065-021-00188-8.

Comparative transcriptomic analysis of the tea plant (Camellia sinensis) reveals key genes involved in pistil deletion

Background

The growth process of the tea plant (Camellia sinensis) includes vegetative growth and reproductive growth. The reproductive growth period is relatively long (approximately 1.5 years), during which a large number of nutrients are consumed, resulting in reduced tea yield and quality, accelerated aging, and shortened economic life of the tea plant. The formation of unisexual and sterile flowers can weaken the reproductive growth process of the tea plant. To further clarify the molecular mechanisms of pistil deletion in the tea plant, we investigated the transcriptome profiles in the pistil-deficient tea plant (CRQS), wild tea plant (WT), and cultivated tea plant (CT) by using RNA-Seq.

Results

A total of 3683 differentially expressed genes were observed between CRQS and WT flower buds, with 2064 upregulated and 1619 downregulated in the CRQS flower buds. These genes were mainly involved in the regulation of molecular function and biological processes. Ethylene synthesis–related ACC synthase genes were significantly upregulated and ACC oxidase genes were significantly downregulated. Further analysis revealed that one of the WIP transcription factors involved in ethylene synthesis was significantly upregulated. Moreover, AP1 and STK, genes related to flower development, were significantly upregulated and downregulated, respectively.

Conclusions

The transcriptome analysis indicated that the formation of flower buds with pistil deletion is a complex biological process. Our study identified ethylene synthesis, transcription factor WIP, and A and D-class genes, which warrant further investigation to understand the cause of pistil deletion in flower bud formation.

Physiological genetics, chemical composition, health benefits and toxicology of tea (Camellia sinensis L.) flower: A review

The flower of tea (Camellia sinensis L.) plant has been paid an increasing attention in the last twenty years, since it was found that tea flowers contained representative constituents similar to those of tea leaves, such as catechins, caffeine and amino acids. Tea flower is theoretically valuable although it has been considered as an industrial waste over a long period of time. This review summarizes the research findings conducted until now on physiological genetics, chemical composition, health benefits and toxicology of tea flowers, aiming to foresee their future applications. A lot of genes are involved in flower development and the synthesis and transmission of various chemicals in tea flowers. The chemical composition of tea flower consists mainly of catechins, polysaccharides, proteins, amino acids and saponins and thus tea flower possesses various health benefits such as antioxidant, anti-inflammatory, immunostimulating, antitumor, hypoglycemic, anti-obesity and anti-allergic activities. Moreover, tea flower contains a protease that can elevate the free amino acids content in the tea infusion by almost two folds. More importantly, the enzymatic activity of the protease is much higher than that of the commercially available proteases. Additionally, aqueous extracts of tea flower are demonstrated to safe to animals. Thus, the potential uses of tea flowers in food and medical fields are warranted.

Comparative transcriptome analysis reveals gene expression differences between two peach cultivars under saline-alkaline stress

BACKGROUND

Saline-alkaline stress is a major abiotic stress that is harmful to plant growth worldwide. Two peach cultivars (GF677 and Maotao) display distinct phenotypes under saline-alkaline stress. The molecular mechanism explaining the differences between the two cultivars is still unclear.

RESULTS

In the present study, we systematically analysed the changes in GF677 and Maotao leaves upon saline-alkaline stress by using cytological and biochemical technologies as well as comparative transcriptome analysis. Transmission electron microscopy (TEM) observations showed that the structure of granum was dispersive in Maotao chloroplasts. The biochemical analysis revealed that POD activity and the contents of chlorophyll a and chlorophyll b, as well as iron, were notably decreased in Maotao. Comparative transcriptome analysis detected 881 genes with differential expression (including 294 upregulated and 587 downregulated) under the criteria of |log2 Ratio| ≥ 1 and FDR ≤0.01. Gene ontology (GO) analysis showed that all differentially expressed genes (DEGs) were grouped into 30 groups. MapMan annotation of DEGs showed that photosynthesis, antioxidation, ion metabolism, and WRKY TF were activated in GF677, while cell wall degradation, secondary metabolism, starch degradation, MYB TF, and bHLH TF were activated in Maotao. Several iron and stress-related TFs (ppa024966m, ppa010295m, ppa0271826m, ppa002645m, ppa010846m, ppa009439m, ppa008846m, and ppa007708m) were further discussed from a functional perspective based on the phylogenetic tree integration of other species homologues.

CONCLUSIONS

According to the cytological and molecular differences between the two cultivars, we suggest that the integrity of chloroplast structure and the activation of photosynthesis as well as stress-related genes are crucial for saline-alkaline resistance in GF677. The results presented in this report provide a theoretical basis for cloning saline-alkaline tolerance genes and molecular breeding to improve saline-alkaline tolerance in peach.