Sugar-inducible gene expression and vacuolar accumulation of storage proteins

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By yeast one-hybrid screen with DNA fragment containing two sequence motifs conserved among the sugar-inducible genes of sweet potato tuberous roots, two tobacco cDNAs coding for putative transcription factors with unknown function were isolated. One of them codes for a protein with HD-Zip domain that binds to Box 3 motif and contains activation domain in its C-terminus. Another one codes for a novel class of bZIP factor. Map-based cloning of lbal mutant of Arabidopsis thaliana that shows reduced sugar-inducible expression of Atβ-Amy gene and accumulation of anthocyanin resulted in identification of a mutation that accompany Gly to Glu substitution in a large protein with unknown function. Among 55 mutants that show altered sugar-inducible expression of Spo^<min> : : LUC reporter. we identified hsi2 by map-based cloning. HSI2 was a novel protein with B3 DNA binding domain and analysis of null-mutant and overexpressor indicated that HSI2 is a reptessor of Spo^<min>. By screening of acti … More vation tagging lines of Spo^<min> : : LUC transgenic plant, three clones that express LUC reporter under low-sugar condition were identified. In these mutants, expression of genes encoding bZIP factor, CCT motif protein and AP2 domain protein with unknown functions were elevated by insertion of enhancer. In particular, enhanced expression of the novel bZIP resulted in enhanced expression of some of the endogenous sugar-inducible genes in addition to Spo^<min> : :LUC. By using oligo-microarray covering all genes of Arabidopsis, we identified transcription factor genes whoes expression is rapidly induced or repressed by sugars in a cycloheximide-insensitive manner. Among these. AtbZIP 22 was found to be required for the sugar-inducible expression of PR-1 gene, and the sugar-repressible AtbZIP63 was shown to be involved in the sugar starvation-induced gene expression. We also found that sugar induces expression of a large number of genes involved in ribosome biogenesis, and nucleolin plays an important role in the regulation of ribosome biogenesis. Less