The heavy metal-associated isoprenylated plant protein (HIPP) gene family plays a crucial role in cadmium resistance and accumulation in the tea plant (Camellia sinensis L.).

Heavy metal-associated isoprenylated plant proteins (HIPPs) are only distributed in vascular plants, and are essential for the detoxification and vascular transport of heavy metals in plants. However, the HIPP gene family has not been thoroughly explored in the tea plant (Camellia sinensis). In this study, we systematically identified 56C. sinensis CsHIPP genes from five groups and characterized their phylogeny, structures, and the features of the encoded proteins. The expression patterns of CsHIPP genes in various tissues of C. sinensis were investigated based on a previous RNA-seq data analysis. The expression patterns of CsHIPP genes were explored in cadmium (Cd)-treated C. sinensis roots using our RNA-seq data. Three CsHIPP genes (CsHIPP22, CsHIPP24, and CsHIPP36) with high expression levels in Cd-treated C. sinensis roots were selected as candidate genes associated with Cd tolerance. Overexpression of CsHIPP22, CsHIPP24, and CsHIPP36 in a yeast mutant (ycf1) rescued Cd-sensitive ycf1 yeast and increased the yeast resistance to Cd stress, implying that these three CsHIPPs might be involved in Cd tolerance. These findings will enable the roles of HIPPs in Cd absorption and detoxification to be better understood as well as improving our understanding of the Cd-resistance and Cd-accumulation mechanisms in tea plant.

Transcriptome Analysis Reveals Differentially Expressed Genes Involved in Cadmium and Arsenic Accumulation in Tea Plant (Camellia sinensis).

Tea (Camellia sinensis) is the second most consumed drink in the world. Rapid industrialization has caused various impacts on nature and increased pollution by heavy metals. However, the molecular mechanisms of cadmium (Cd) and arsenic (As) tolerance and accumulation in tea plants are poorly understood. The present study focused on the effects of heavy metals Cd and As on tea plants. Transcriptomic regulation of tea roots after Cd and As exposure was analyzed to explore the candidate genes involved in Cd and As tolerance and accumulation. In total, 2087, 1029, 1707, and 366 differentially expressed genes (DEGs) were obtained in Cd1 (with Cd treatment for 10 days) vs. CK (without Cd treatment), Cd2 (with Cd treatment for 15 days) vs. CK, As1 (with As treatment for 10 days) vs. CK (without Cd treatment), and As2 (with As treatment for 15 days) vs. CK, respectively. Analysis of DEGs showed that a total of 45 DEGs with the same expression patterns were identified in four pairwise comparison groups. One ERF transcription factor (CSS0000647) and six structural genes (CSS0033791, CSS0050491, CSS0001107, CSS0019367, CSS0006162, and CSS0035212) were only increased at 15 d of Cd and As treatments. Using weighted gene co-expression network analysis (WGCNA) revealed that the transcription factor (CSS0000647) was positively correlated with five structural genes (CSS0001107, CSS0019367, CSS0006162, CSS0033791, and CSS0035212). Moreover, one gene (CSS0004428) was significantly upregulated in both Cd and As treatments, suggesting that these genes might play important roles in enhancing the tolerance to Cd and As stresses. These results provide candidate genes to enhance multi-metal tolerance through the genetic engineering technology.

Genome-wide identification and characterization of PdbHLH transcription factors related to anthocyanin biosynthesis in colored-leaf poplar (Populus deltoids).

Basic helix-loop-helix (bHLH) proteins are transcription factors (TFs) that have been shown to regulate anthocyanin biosynthesis in many plant species. However, the bHLH gene family in Populus deltoids has not yet been reported. In this study, 185 PdbHLH genes were identified in the Populus deltoids genome and were classified into 15 groups based on their sequence similarity and phylogenetic relationships. Analysis of the gene structure, chromosome location and conserved motif of the PdbHLH genes were performed by bioinformatic methods. Gene duplication analyses revealed that 114 PdbHLH were expanded and retained after WGD/segmental and proximal duplication. Investigation of cis-regulatory elements of PdbHLH genes indicated that many PdbHLH genes are involved in the regulation of anthocyanin biosynthesis. The expression patterns of PdbHLHs were obtained from previous data in two colored-leaf poplar (QHP and JHP) and green leaf poplar (L2025). Further analysis revealed that 12 candidate genes, including 3 genes (PdbHLH57, PdbHLH143, and PdbHLH173) from the subgroup III(f) and 9 gene from other groups, were positively associated with anthocyanin biosynthesis. In addition, 4 genes (PdbHLH4, PdbHLH1, PdbHLH18, and PdbHLH164) may be involved in negatively regulating the anthocyanin biosynthesis. These results provide a basis for the functional characterization of bHLH genes and investigations on the molecular mechanisms of anthocyanin biosynthesis in colored-leaf poplar.