Molecular mechanism of Al tolerance and development of Al tolerant crop

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In order to isolate Al tolerant gene, we screened 16,000 activation tagging line of Arabidopsis and found 20 candidates lines. However, almost all candidate lines showed the multiple copy of the tag in chromosome. Only one lien (#355-2) showed an insertion of single copy at upstream region of chromosome 1.To vivify the role of mitochondria on the molecular mechanism of Al toxicity and tolerance, we used Al sensitive tobacco line(SL) and tolerant line (ALT301). We observed a decrease in State III and IV respiration in both SL with reduced rate of inhibition in ALT301.In SL,AOX- and CYT-respirations were inhibited but AOX-respiration in ALT301 increased by 15%. Production of ROS in mitochondria of SL increased but it deceased in ALT301 under Al stress.We succeeded to isolate novel gene (ALMT1) encoding Al activated malate transporter from near isogenic Al tolerant wheat (ET8). ALMT1-1 were common in Al tolerant ET8 and Atlas 66. ALMT1-2 were common in Al sensitive ES8 and Scout 66. The difference between ALMT1-1 and ALMT1-2 were 6 bases (2 amino acid residues). ALMT1-1 segregated well to Al tolerance of wheat, suggesting that ALMT1-1 corresponds to Al tolerance (Alt 1) gene.Heterogous expression of ALMT1 in Xonopus oocytes, rice and cultured tobacco ells conferred an Al-activated malate efflux. We generated transgenic barley plants expressing ALMT1. ALMT1 expression in barley conferred an Al-activated efflux of malate. The transgenic barley showed a high level of Al tolerance when grown in both hydroponics culture and on acid soils.