Genetic And Molecular Mechanisms Of Aluminum Tolerance In Upland Rice (Oryza Sativa L.)

Aluminum (Al) toxicity is a major factor limiting plant growth on acid soil. Al toxicity inhibits root growth, and then limits plant from absorbing water and other nutrients, and consequently reduces plant growth. In this study, an upland tropical japonica rice Azucena and a lowland indica rice 1R1552 were used for screening Al induced gene. A recombinant inbred line (RIL) population derived from a cross between IR1552 and Azucena were used for detecting QTLs for tolerance to Al toxicity at different seedling stages. Comparative mapping analysis was carried out for the QTLs reported for rice rolerance to Al toxicity from different genetic populations. cDNA-AFLP was used for identifying Al induced genes. All of the 34 TDFs were aligned to integrated genetic and physical map by sequence alignment or genetic mapping. ESTs mapped at the detected QTL interval were screened by reverse Northern. The results were summarized as follows:1. QTLs for Al tolerance were identified by using the RIL population described as above. Three QTLs were detected after both one week and two weeks of Al to stress at the interval RZ801-RG381, RZ698-AC A-CTA1 and ACA-CTT1-RM117 on chromosome 1, 9 and 12, respectively. The 3 QTLs accounted about 39% and 35% of total variation in root length after one week Al stress treatment and two weeks stress streatment, respectively. The QTL on chromosome 1 explained about 15% and 9% of phenotypic variation after 1 and 2 weeks of Al stress with positive allelic effect from Azucena. Positive allele of QTLs on chromosome 9 is from IR1552 which explained about 13% and 15% of total phenotypic variation. The QTL on chromosome 12 explained about 10% and 11% of phenotypic variation with positive allele(s) from Azucena. By integrated mapping based on rice genetic map, an identical QTL interval between C86 and C742 were found on chromosome 1 from 4 different genetic populations.2. Thirty four Al induced TDFs were screened by cDNA-AFLP, including 33 unique genes. Of 33 unique genes, 19 showed homoiogy with known genes. Seven of the 19 genes are involved in cell wall components metabolism, 3 for cellular metabolism, 3 for protein metabolism and 6 for secondary metabolism, oxidative stress and other metabolic pathways. The result indicates that Al toxicity affected different physiological and biochemical pathways.3. Two Al induced genes (OsAR16, OsAR28) located near the QTL interval on chromosome 1 were singled out by cDNA-AFLP. According to the transcription map, 83 ESTs located between C86 and C742 were screened. Four Al induced ESTs were confirmed by Northen blot analysis. The 4 genes are for amino acid transport protein (C50531), non-specific lipid transfer protein (E30131), Rho GDP-dissociation inhibitor (E1391) and Ubiquitin-like protein SUMO-1 (E61853). One of the 4 ESTs (E61853) showed homoiogy with OsAR16. Full length CDS of OsAR28 was obtained by PCR according to the predicted results of bioinformatics. This CDS was 513bp, which showed homoiogy (98%) with first 510 bp of another predicted gene in chromosome 1. Blast results showed that it was homoiogy with an exosome complex exonuclease (45% in Blastn). Further work need to be performed for confirming if this gene show any relationship with Al tolerance in rice.