Transcriptome-wide analysis of MADS-box family genes involved in aluminum and fluoride assimilation in Camellia sinensis.

MADS-box transcription factors (TFs) are involved in a variety of processes in flowering plants ranging from root growth to flower and fruit development. However, studies of the tolerance-related functions of MADS-box genes are very limited, and to date no such studies have been conducted on Camellia sinensis. To gain insight into the functions of genes of this family and to elucidate the role they may play in tissue development and Al and F response, we identified 45 MADS-box genes through transcriptomic analysis of C. sinensis. Phylogenetic analysis of these CsMADS-box genes, along with their homologues in Arabidopsis thaliana, enabled us to classify them into distinct groups, including: M-type (Mα), MIKC* and MIKCc (which contains the SOC1, AGL12, AGL32, SEP, ANR1, SVP, and FLC subgroups). Conserved motif analysis of the CsMADS-box proteins revealed diverse motif compositions indicating a complex evolutionary relationship. Finally, we examined the expression patterns of CsMADS-box genes in various tissues and under different Al and F concentration treatments. Our qPCR results showed that these CsMADS-box genes were involved in Al and F accumulation and root growth in C. sinensis. These findings lay the foundation for future research on the function of CsMADS-box genes and their role in response to Al and F accumulation in root tissues.

Cell wall pectin methyl-esterification and organic acids of root tips involve in aluminum tolerance in Camellia sinensis.

Tea plant (Camellia sinensis (O.) Kuntze) can survive from high levels of aluminum (Al) in strongly acidic soils. However, the mechanism driving its tolerance to Al, the predominant factor limiting plant growth in acid condition, is still not fully understood. Here, two-year-old rooted cuttings of C. sinensis cultivar 'Longjingchangye' were used for Al resistance experiments. We found that the tea plants grew better in the presence of 0.4 mM Al than those grew under lower concentration of Al treatments (0 and 0.1 mM) as well as higher levels treatment (2 and 4 mM), confirming that appropriate Al increased tea plant growth. Hematoxylin staining assay showed that the apical region was the main accumulator in tea plant root. Subsequently, immunolocalization of pectins in the root tip cell wall showed a rise in low-methyl-ester pectin levels and a reduction of high-methyl-ester pectin content with the increasing Al concentration of treatments. Furthermore, we observed the increased expressions of C. sinensis pectin methylesterase (CsPME) genes along with the increasing de-esterified pectin levels during response to Al treatments. Additionally, the levels of organic acids increased steadily after treatment with 0.1, 0.4 or 2 mM Al, while they dropped after treatment with 4 mM Al. The organic acids secretion from root followed a similar trend. Similarly, a gradual increase in malate dehydrogenase (MDH), citrate synthase (CS) and glycolate oxidase (GO) enzyme activities and relevant metabolic genes expression were detected after the treatment of 0.1, 0.4 or 2 mM Al, while a sharp decrease was resulted from treatment with 4 mM Al. These results confirm that both pectin methylesterases and organic acids contribute to Al tolerance in C. sinensis.

Gene expression profile indicates involvement of NO in Camellia sinensis pollen tube growth at low temperature.

BACKGROUND: Nitric oxide (NO) functions as a critical signaling molecule in the low-temperature stress responses in plants, including polarized pollen tube growth in Camellia sinensis. Despite this, the potential mechanisms underlying the participation of NO in pollen tube responses to low temperature remain unclear. Here, we investigate alterations to gene expression in C. sinensis pollen tubes exposed to low-temperature stress and NO using RNA-Seq technology, in order to find the potential candidate genes related to the regulation of pollen tube elongation by NO under low-temperature stress. RESULTS: Three libraries were generated from C. sinensis cv. 'Longjingchangye' pollen tubes cultured at 25 °C (CsPT-CK) and 4 °C (CsPT-LT) or with 25 µM DEA NONOate (CsPT-NO). The number of unigenes found for the three biological replications were 39,726, 40,440 and 41,626 for CsPT-CK; 36,993, 39,070 and 39,439 for CsPT-LT; and 39,514, 38,298 and 39,061 for CsPT-NO. A total of 36,097 unique assembled and annotated sequences from C. sinensis pollen tube reads were found in a BLAST search of the following databases: NCBI non-redundant nucleotide, Swiss-prot protein, Kyoto Encyclopedia of Genes and Genomes, Cluster of Orthologous Groups of proteins, and Gene Ontology. The absolute values of log2Ratio > 1 and probability > 0.7 were used as the thresholds for significantly differential gene expression, and 766, 497 and 929 differentially expressed genes (DEGs) were found from the comparison analyses of the CK-VS-LT, CK-VS-NO and LT-VS-NO libraries, respectively. Genes related to metabolism and signaling pathways of plant hormones, transcription factors (TFs), vesicle polarized trafficking, cell wall biosynthesis, the ubiquitination machinery of the ubiquitin system and species-specific secondary metabolite pathways were mainly observed in the CK-VS-LT and CK-VS-NO libraries. CONCLUSION: Differentially expressed unigenes related to the inhibition of C. sinensis pollen tube growth under low temperature and NO are identified in this study. The transcriptomic gene expression profiles present a valuable genomic tool to improve studying the molecular mechanisms underlying low-temperature tolerance in pollen tube.

Combined Cytological and Transcriptomic Analysis Reveals a Nitric Oxide Signaling Pathway Involved in Cold-Inhibited Camellia sinensis Pollen Tube Growth.

Nitric oxide (NO) as a signaling molecule plays crucial roles in many abiotic stresses in plant development processes, including pollen tube growth. Here, the signaling networks dominated by NO during cold stress that inhibited Camellia sinensis pollen tube growth are investigated in vitro. Cytological analysis show that cold-induced NO is involved in the inhibition of pollen tube growth along with disruption of the cytoplasmic Ca(2+) gradient, increase in ROS content, acidification of cytoplasmic pH and abnormalities in organelle ultrastructure and cell wall component distribution in the pollen tube tip. Furthermore, differentially expressed genes (DEGs)-related to signaling pathway, such as NO synthesis, cGMP, Ca(2+), ROS, pH, actin, cell wall, and MAPK cascade signal pathways, are identified and quantified using transcriptomic analyses and qRT-PCR, which indicate a potential molecular mechanism for the above cytological results. Taken together, these findings suggest that a complex signaling network dominated by NO, including Ca(2+), ROS, pH, RACs signaling and the crosstalk among them, is stimulated in the C. sinensis pollen tube in response to cold stress, which further causes secondary and tertiary alterations, such as ultrastructural abnormalities in organelles and cell wall construction, ultimately resulting in perturbed pollen tube extension.