CsPDC-E1α, a novel pyruvate dehydrogenase complex E1α subunit gene from Camellia sinensis, is induced during cadmium inhibiting pollen tube growth

Cadmium (Cd) is one of the most toxic heavy metal pollutants highly hazardous to pollen tubes by disrupting mitochondria. Mitochondrial pyruvate dehydrogenase complex (PDC) plays an important role in cellular metabolism and links cytosolic glycolytic metabolism to the tricarboxylic acid cycle. However, the relationship between PDC, pollen germination, and pollen tube growth under Cd stress remains unclear. Here, we found that Cd inhibited Camellia sinensis (L.) Kuntze pollen germination and pollen tube growth in a dose-dependent manner and disrupted the tip clear zone of the pollen tube. Furthermore, we isolated a novel PDC gene (CsPDC-E1 alpha) from C. sinensis. The full-length cDNA of CsPDC-E1 alpha was 1606 bp and encoded a 393 amino acid protein containing a typical PDC thiamine pyrophosphate (TPP) binding site, heterodimer interface, phos-phorylation loop region, and tetramer interface domain, suggesting that CsPDC-E1 alpha was a member of the PDC_ADC_BCADC subfamily in the TPP family. Bioinformatics analysis indicated that the CsPDC-E1 alpha protein shared a high degree of homology with that from Petunia x hybrida. The CsPDC-E1 alpha relative expression levels in pollen were significantly higher than other tissues of C. sinensis, indicating that CsPDC-E1 alpha expression is tissue-specific. To confirm the functions of CsPDC-E1 alpha in pollen response to Cd stress, we analyzed the relative expression level of CsPDC-E1 alpha in Cd-treated pollen tubes and found that the expression of CsPDC-E1 alpha was induced by Cd stress. All these results indicate that CsPDC-E1 alpha might be associated with Cd inhibition of C. sinensis pollen germination and pollen tube growth.