Cloning and characterization of a SnRK1-encoding gene from <Emphasis Type="Italic">Malus hupehensis</Emphasis> Rehd. and heterologous expression in tomato

Sucrose non-fermenting-1-related protein kinase-1 (SnRK1) plays an important role in metabolic regulation in plant. To understand the molecular mechanism of amino acids and carbohydrate metabolism in Malus hupehensis Rehd. var. pinyiensis Jiang (Pingyi Tiancha, PYTC), a full-length cDNA clone encoding homologue of SnRK1 was isolated from PYTC by Rapid Amplification of cDNA Ends (RACE). The clone, designated as MhSnRK1, contains 2063 nucleotides with an open reading frame of 1548 nucleotides. The deduced 515 amino acids showed high identities with other plant SnRK1 genes. Quantitative real-time PCR analysis revealed this gene was expressed in roots, stems and leaves. Exposing seedlings to nitrate caused and initial decrease in expression of the MhSnRK1 gene in roots, leaves and stems in short term. Ectopic expression of MhSnRK1 in tomato mainly resulted in higher starch content in leaf and red-ripening fruit than wild-type plants. This result supports the hypothesis that overexpression of SnRK1 causes the accumulation of starch in plant cells. All the results suggest that MhSnRK1 may play important roles in carbohydrate and amino acid metabolisms.     

<Emphasis Type="Italic">IiSDD1</Emphasis>, a gene responsive to autopolyploidy and environmental factors in <Emphasis Type="Italic">Isatis indigotica</Emphasis>

In plants, stomata play a pivotal role in the regulation of gas exchange and are distributed throughout the aerial epidermis. SDD1, a gene isolated from Arabidopsis thaliana has been demonstrated to specialize in stomatal density and distribution. In our present study, a comprehensive survey of global gene expression performed by using an A. thaliana whole genome Affymetrix gene chip revealed SDD1 tends to be significantly lower in tetraploid Isatis indigotica than in diploid ones. To intensively investigate different SDD1 expression in response to polyploidy, a full-length cDNA clone (IiSDD1) encoding SDD1 was isolated from the traditional Chinese medicinal herb I. indigotica cDNA library. IiSDD1 shared a high level of identity with that from A. thaliana, containing some basic features of subtilases: D, H and S regions, as well as a substrate-binding site. Real-time quantitative PCR analysis indicated that IiSDD1 was constitutively expressed in all tested tissues, including roots, stems and leaves, both in tetraploid and diploid I. indigotica, and with the highest expression in leaves. In addition, IiSDD1 was also found to be down-regulated by signalling molecules for plant defence responses, such as abscisic acid (100 μM) and gibberellin (100 mg/L), as well as by environmental stresses including salt, darkness, coldness and drought. Our study, for the first time, indicates SDD1 participates not only in the defense/stress responsive pathways, but also probably involves in plants polyploidy evolution.     

<Emphasis Type="Italic">Anthocyaninless1</Emphasis> gene of <Emphasis Type="Italic">Arabidopsis thaliana</Emphasis> encodes a UDP-glucose:flavonoid-3-<Emphasis Type="Italic">O</Emphasis>-glucosyltransferase

We isolated several mutants of Arabidopsis thaliana (L.) Heynh. that accumulated less anthocyanin in the plant tissues, but had seeds with a brown color similar to the wild-type. These mutants were allelic with the anthocyaninless1 (anl1) mutant that has been mapped at 15.0 cM of chromosome 5. We performed fine mapping of the anl1 locus and determined that ANL1 is located between the nga106 marker and a marker corresponding to the MKP11 clone. About 70 genes are located between these two markers, including three UDP-glucose:flavonoid-3-O-glucosyltransferase-like genes and a glutathione transferase gene (TT19). A mutant of one of the glucosyltransferase genes (At5g17050) was unable to complement the anl1 phenotype, showing that the ANL1 gene encodes UDP-glucose:flavonoid-3-O-glucosyltransferase. ANL1 was expressed in all tissues examined, including rosette leaves, stems, flower buds and roots. ANL1 was not regulated by TTG1.