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The citrus cultivar Carrizo is the single most important rootstock to the US citrus industry and has resistance or tolerance to a number of major citrus diseases, including citrus tristeza virus, foot rot, and Huanglongbing (HLB, citrus greening). A Carrizo genomic sequence database providing approximately 3.5× genome coverage (haploid genome size approximately 367 Mb) was populated through 454 GS FLX shotgun sequencing. Analysis of the repetitive DNA fraction indicated a total interspersed repeat fraction of 36.5%. Assembly and characterization of abundant citrus Ty3/ gypsy elements revealed a novel type of element containing open reading frames encoding a viral RNA-silencing suppressor protein ( RNA binding protein, rbp) and a plant cytokinin riboside 5′-monophosphate phosphoribohydrolase-related protein ( LONELY GUY, log). Similar gypsy elements were identified in the Populus trichocarpa genome. Gene-coding region analysis indicated that 24.4% of the nonrepetitive reads contained genic regions. The depth of genome coverage was sufficient to allow accurate assembly of constituent genes, including a putative phloem-expressed gene. The development of the Carrizo database () will contribute to characterization of agronomically significant loci and provide a publicly available genomic resource to the citrus research community. [ABSTRACT FROM AUTHOR]

Abstract: Steroidal glycoalkaloids (SGAs) are potentially harmful specialty metabolites found in Solanaceous plants. Two tri-glycosylated alkaloids, α-chaconine and α-solanine accumulate in potato tubers. Expressed sequence tags (ESTs) were identified in the available database by searching for protein homology to the Sgt1 (SOLtu:Sgt1) steriodalalkaloid galactosyltransferase. The EST sequence data was used to isolate Sgt3 cDNA sequences by polymerase chain reaction (PCR) from a wounded potato tuber cDNA library. The resulting 1515bp open reading frame of Sgt3, encodes a predicted SGT3 amino acid sequence that is 18 residues longer than, 45% identical to, and 58% homologous to the SGT1 protein. The amino-terminal region of the Sgt3 cDNA was used to create an antisense transgene under control of the granule bound starch synthase, GBSS6, promoter and the ubiquitin, Ubi3, polyadenylation signal. Analysis of SGA metabolites in selected transgenic tubers revealed a dramatic decrease in the accumulation of α-chaconine and α-solanine. This decrease was compensated by an increase in β-solanine and β-chaconine with minor accumulation of α-SGAs. These results allowed the identification of the function for SGT3 as the β-solanine/β-chaconine rhamnosyl transferase, the terminal step in formation of the potato glycoalkaloid triose side chains. [Copyright &y& Elsevier]

Abstract: To provide tools for breeders to control the steroidal glycoalkaloid (SGA) pathway in potato, we have investigated the steroidal alkaloid glycosyltransferase (Sgt) gene family. The committed step in the SGA pathway is the glycosylation of solanidine by either UDP-glucose or UDP-galactose leading to α-chaconine or α-solanine, respectively. The Sgt2 gene was identified by deduced protein sequence homology to the previously identified Sgt1 gene. SGT1 has glucosyltransferase activity in vitro, but in vivo serves as the UDP-galactose:solanidine galactosyltransferase. Two alleles of the Sgt2 gene were isolated and its function was established with antisense transgenic lines and in vitro assays of recombinant protein. In tubers of transgenic potato (Solanum tuberosum) cvs. Lenape and Desirée expressing an antisense Sgt2 gene construct, accumulation of α-solanine was increased and α-chaconine was reduced. Studies with recombinant SGT2 protein purified from yeast show that SGT2 glycosylation activity is highly specific for UDP-glucose as a sugar donor. This data establishes the function of the gene product (SGT2), as the primary UDP-glucose:solanidine glucosyltransferase in vivo. [Copyright &y& Elsevier]

Steroidal glycoalkaloids (SGAs) are secondary metabolites of Solanaceous plants. Two predominant glycoalkaloids, α-chaconine and α-solanine are produced in potatoes. An antisense transgene was constructed to down-regulate glycoalkaloid biosynthesis using a potato cDNA encoding a sterol alkaloid glycosyltransferase (Sgt1). Introduction of this construct into potatoes resulted in some lines with an almost complete inhibition of α-solanine accumulation. This inhibition was compensated by elevated levels of α-chaconine and resulted in wild type total SGA levels in the transgenic lines. In vitro assays with the recombinant SGT1 isolated from yeast demonstrated that Sgt1 encodes an enzyme capable of both glucosyltransferase and galactosyltransferase activity with a preference for UDP-galactose as the sugar donor. Together this data confirms SGT1''s role in vivo as the solanidine:UDP-galactose galactosyltransferase. [Copyright &y& Elsevier]