Diversity and expression of diatom silicon transporter genes during a flood event in the East China Sea

Abstract

Diatoms are responsible for 75 % of the primary production in high-nutrient and coastal regions of the ocean, and their growth is sometimes limited by silicon availability. We investigated the genetic diversity of silicon transporter (Sit) genes and measured Sit gene expression in one dominant genus, Chaetoceros, as a molecular indicator of silicon deficiency in the East China Sea (ECS). A total of 34 Sit fragments were sequenced from species belonging to 13 genera. These sequences covered 12 genera of which no Sit sequences have been previously reported; thus, this information has greatly expanded the Sit gene database. These sequences were combined with the existing Sit sequences in GenBank, and the combined set was used to sort the homologous Sit identified in the ECS. Based on the Sit sequence alignments, specific primers were designed for the Chaetoceros genus to quantitatively estimate Sit expression levels using quantitative RT-PCR. In a cruise conducted in July 2010, the observed Chaetoceros Sit transcript levels were comparable in range to those detected in the species, C. affinis, cultured under silicon-sufficient conditions. This finding may be explained by the devastating 2010 flood of the Changjiang River, which resulted in the influx of a large amount of silicic acid to the ECS.