Study of Arabidopsis β-amylases and a starch excess mutant ke103
Date Issued
2007
Date
2007
Author(s)
Lin, Yen-Lung
DOI
zh-TW
Abstract
Transitory starch is synthesized in chloroplast during the light period and broken-down at night. The products of starch degradation are exported to cytosol and transported through out the plant. Recent studies suggest that beta-amylase activity is essential for transitory starch degradation. Four of the nine beta-amylases encoded in the Arabidopsis thaliana genome are predicted to be chloroplastic. Mutants of those genes were studied. Plants with mutation in BAM3 and BAM4 were reported to accumulate starch at night. Down-regulation of BAM1 or BAM2 didn’t result in the same phenotype, nevertheless, the dramatically high starch content of the quadruple mutant line bam1/bam2/bam3/bam4 suggested that the activities of BAM1 and BAM2 were not negligible. The starch excess mutant ke103 lost its BAM1 activity band in a glycogen gel-based amylase activity assay, so did the knock-out mutant of BAM1, bam1-1. Interestingly, the activity can be recovered by mixing these two samples. In vitro complementation of these mutants indicated that BAM1 can interact with a protein either encoded directly by KE103 or activated by a KE103 encoded protein. The starch content of bam1-1 is similar to that of the wild type. However, the starch content was higher in ke103/bam1-1 double mutant than in ke103, indicating that ke103 didn’t influence on starch degradation via BAM1. To further understand the function of KE103, mapping populations with F2 progeny from ke103 x Ler and Col x ke103, were established to map ke103, and a series of SNP markers were identified using CEL I nuclease. We found that ke103 co-segregated with a SSLP marker nga172. The recombination frequency between ke103 and SNP markers illustrated that ke103 located between 1.0 Mb and 1.33 Mb of chromosome 3. The early steps of transitory starch degradation remain largely unknown. It was postulated that a beta-amylase may act in concert with a debranching enzyme to attack the starch granule. The results of yeast-two-hybrid assay showed that the isoamylase ISA3 cannot interact with beta-amylases BAM1, BAM3, or BAM4. And no evidence was found to support that they would interact through the mediation of other proteins. BAM1 transcript expression was induced by salt stress. The starch of Col WT is degraded faster in salt stress than that of controls, while the starch metabolism of bam1-1 is not altered in salt stress. This result suggested that BAM1 may respond to salt stress.
Subjects
暫儲性澱粉
beta澱粉水解酶
鹽分逆境
ke103
BAM1
transitory starch
beta-amylase
salt stress
Type
other
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