Combined de novo transcriptomic and physiological analyses reveal RyALS3-mediated aluminum tolerance in Rhododendron yunnanense Franch.

Rhododendron (Ericaceae) not only has ornamental value, but also has great medicinal and edible values. Many Rhododendron species are native to acid soils where aluminum (Al) toxicity limits plant productivity and species distribution. However, it remains unknown how Rhododendron adapts to acid soils. Here, we investigated the physiological and molecular mechanisms of Al tolerance in Rhododendron yunnanense Franch. We found that the shoots of R. yunnanense Franch did not accumulate Al after exposure of seedlings to 50 µM Al for 7 days but predominantly accumulated in roots, suggesting that root Al immobilization contributes to its high Al tolerance. Whole-genome de novo transcriptome analysis was carried out for R. yunnanense Franch root apex in response to 6 h of 50 µM Al stress. A total of 443,639 unigenes were identified, among which 1,354 and 3,413 were up- and down-regulated, respectively, by 6 h of 50 µM Al treatment. Both Gene Ontology (GO) enrichment and the Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analyses revealed that genes involved in "ribosome" and "cytoskeleton" are overrepresented. Additionally, we identified Al-tolerance homologous genes including a tonoplast-localized ABC transporter RyALS3; 1. Overexpression of RyALS3; 1 in tobacco plants confers transgenic plants higher Al tolerance. However, root Al content was not different between wild-type plants and transgenic plants, suggesting that RyALS3; 1 is responsible for Al compartmentalization within vacuoles. Taken together, integrative transcriptome, physiological, and molecular analyses revealed that high Al tolerance in R. yunnanense Franch is associated with ALS3; 1-mediated Al immobilization in roots.

Integrated transcriptome and amino acid profile analyses reveal novel insights into differential accumulation of theanine in green and yellow tea cultivars.

Tea cultivars with yellow- or white-leaf variations have a high economic value due to their high amino acid (especially theanine) concentration. However, the dynamic changes of amino acid components (especially theanine) and related gene expression during new shoot development in these cultivars are still unclear. In this study, 264 tea samples from four representative varieties picked during the harvest period in spring were analyzed for their amino acid profiles. The dynamic change rules of ethylamine and 19 amino acids were summarized in normal green and yellow cultivars during new shoot development. Interestingly, the theanine concentration in the yellow cultivar was significantly higher than that in the green cultivar, and increased gradually as the leaves matured until they reached a maximum in the one bud and three leaves stage. The amino acid concentration in the leaves of the yellow cultivar increased significantly with leaf position, which was generally in contrast to the normal green cultivar. Transcriptome and correlation analyses revealed that CsGS1, CsPDX2, CsGGP5, CsHEMA3 and CsCLH4 might be the key genes potentially responsible for the differential accumulation of theanine in green and yellow tea cultivars. These results provide further information for the utilization and improvement of tea plants.