Comparative physiological and transcriptomic analyses illuminate common mechanisms by which silicon alleviates cadmium and arsenic toxicity in rice seedlings

The inessential heavy metal/loids cadmium (Cd) and arsenic (As), which often co-occur in polluted paddy soils, are toxic to rice. Silicon (Si) treatment is known to reduce Cd and As toxicity in rice plants. To better understand the shared mechanisms by which Si alleviates Cd and As stress, rice seedlings were hydroponically exposed to Cd or As, then treated with Si. The addition of Si significantly ameliorated the inhibitory effects of Cd and As on rice seedling growth. Si supplementation decreased Cd and As translocation from roots to shoots, and significantly reduced Cd- and As-induced reactive oxygen species generation in rice seedlings. Transcriptomics analyses were conducted to elucidate molecular mechanisms underlying the Si-mediated response to Cd or As stress in rice. The expression patterns of the differentially expressed genes in Cd- or As-stressed rice roots with and without Si application were compared. The transcriptomes of the Cd- and As-stressed rice roots were similarly and profoundly reshaped by Si application, suggesting that Si may play a fundamental, active role in plant defense against heavy metal/loid stresses by modulating whole genome expression. We also identified two novel genes, Os01g0524500 and Os06g0514800, encoding a myeloblastosis (MYB) transcription factor and a thionin, respectively, which may be candidate targets for Si to alleviate Cd and As stress in rice, as well as for the generation of Cd- and/or As-resistant plants. This study provides valuable resources for further clarification of the shared molecular mechanisms underlying the Si-mediated alleviation of Cd and As toxicity in rice.