Expression patterns of the rice class I metallothionein gene family in response to lead stress in rice seedlings and functional complementation of its members in lead-sensitive yeast cells

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Metallothioneins (MTs) are a group of low molecular mass and cysteine-rich proteins that can chelate heavy-metal ions. In this paper, Northern blot analysis was used to investigate the influence of lead stress on the expression patterns of 10 rice class I MT genes (OsMT-Is) in rice seedlings. With the exception of OsMT-I-3b, the data demonstrate dynamic changes of 9 OsMT-I transcripts in response to Pb2+ treatment in rice seedling roots. Of these genes, transcription of OsMT-I-1a, OsMT-I-1b, OsMT-I-2c, OsMT-I-4a, OSMT-I-4b and OsMT-I-4c increased significantly, while transcription of OsMT-I-2a and OsMT-I-3a increased marginally. In contrast, the expression of OsMT-I-2b was inhibited. Pb2+ induced the expression of 6 OsMT-I genes in seedling shoots, but had no obvious effects on the expression of OsMT-I-1a, OsMT-I-1b, OsMT-I-4a and OsMT-I-4b. All the 10 OsMT-Is had enhanced lead tolerance when heterologously expressed in lead-sensitive yeast mutant cells. These results provide an expression profile of the rice MT gene family in response to Pb2+ stress in rice seedlings and demonstrate increased lead tolerance in sensitive yeast mutant cells expressing OsMT-Is. This study lays a foundation for further analysis of the role of the rice MT gene family in respond to Pb2+ stress.