Daubert, Stephen D. : Stephen D. Daubert, Postdoctoral Research Associate, Plant Pathology, U.C., Davis

Gardner, Richard C. : Richard C. Gardner, Principal Scientist, Calgene, Inc., Davis.

Shepherd, Robert J. : Robert J. Shepherd, Professor, U.C., Davis

Leaves from turnip plants infected genes via crown gallwill lead to plants that re - with cauliflower mosaic virus . Leaf tain and express new characteristics . In fact , on left is infected with native , similardemonstrations of T - DNA expression virus . Those on right are wild - type in normal plant tissueshave now been accom - from plants infected with mutants plished in at least five other laboratories by insertion of 12s produced additional nucleotide pair into worldwide . the chromosome of the same virus Because the abnormal growth of crown strain . Plants infected with the gall tissues is a major obstacle to crown - gall - mutant on the right grow almost mediated plant genetics , we have also investi - as rapidly as healthy plants . gated the unusual hormone metabolism associated with the disease to determine whether it is the cause of the abnormal growth . The fact that crown gall tissues differ from nontransformed plant tissues in being one ( gene 11 ) is not essential for reproduc - able to grow on a simple nutrient medium tion , enclothement in protein , or cell - to - cell DNA plant viruses lacking auxin and cytokinin suggests that movement . Recent work at Davis indicates crown galls produce these hormones at ele - that this nonessential gene is probably in - Robert J . Shepherd vated rates . Our own studies on cytokininsin volved in insect transmission of the virus in Stephen D . Daubert a variety of crown galls indicate that these nature . These dispensible regions of the virus C . Gardner Richard tissues generally overproduce cytokinins at chromosome provide sites for insertion of 8 - to 1,600 - fold greater levels ranging from foreign DNA , which is carried into the plant than normal . The predominant cytokinins in and replicated along with the DNA of the in - A remarkably simple genetic system for crown galls have been purified and identified fecting virus . study of DNA multiplication and gene ex - as zeatin and ribosylzeatin , which are Another region of the cauliflower mosaic pression in plants is provided by DNA plant N6 - substituted derivatives of adenine and virus chromosome has been identified as viruses . These viruseshave only a half - dozen adenosine , respectively . In addition , crown being responsible for the severity of disease . or sogenesthat are believed to be regulatedin galls with extremelyhigh total cytokinin con - This region is gene VI on the physical map . the same way as other plant genes . The DNA tents contain glucose derivatives of both of The other five genes appear to have little , if replicates in nuclei and may be associated these cytokinins . any , effect on symptom induction . A single with nuclear proteins ( histones ) in the same Presumably , the hormone imbalance re - a profound effect change in gene VI can have as plant genetic material . Thus , the virus way sultingfrom T - DNA expressionin crown gall on disease expression : in one case , insertion provides a small - scale , readily manipulated cells underlies the abnormal growth we ob - of 12 base pairs at a particular location in model for gene expression . serve . We have detected genes on the Ti plas - in - gene VI almost abolished disease . Plants Viruses reproduce in living tissue by sup - mid affecting cytokinin biosynthesis by the fected with this mutant of the virus show very plying a few of their own functions , while fill - C . I . Kado has shown that pathogen , and as mild symptoms and grow at the same rate ing most of their needs by parasitizing the plasmid genes for auxin biosynthesis also ex - healthy plants . Information of this sort may a smallloop host . Each viral particle contains ist . Identifyingthese genesand their products enable the investigator to control disease ex - of nucleic acid , the genetic component , en - is a first step toward controlling them . Ulti - of the viruschromosome pression , if portions clothed in an outer shell of coat protein . The mately , we would like to have effective Ti are eventually used as a recombinant DNA protein is shed soon after the particle enters plasmid vectors that introduce desirable vector for plants . the cell , and the DNA sets about reprogram - genes into plants without also making tumors . as Cauliflower mosaic virus has been used ming the cell to manufacture virus . In carry - a vehicle to reproduce foreign DNA in plant John W Einset , Assistant Professor , Botany and ing out these changes , the virus interferes cells and to carry this foreign DNA from cell Plant Sciences , Cell Interaction Group , U.C . , so that the cell with normal cellular functions Riverside . to cell throughout the entire plant . However , becomes less well coordinated . The organism not enough foreignDNA can be inserted into as a whole is affected and shows disease the virus chromosome to bring about useful symptoms . Reductions in growth rate and transformations of plants . This limitationap - leaf puckering and yellowing are common ef - pears to be related to a low capacity of the of the DNA viruses . fects virus particle to accommodate additional One DNA plant virus , the cauliflower mo - to DNA . Assemblyof DNA and coat protein saic virus , has received more attention than form virus particles seems to be necessary the others . Its biology has been intensively before the DNA will move from cell to cell in studied during the last few years , and the the plant . It does not appear , therefore , that DNA from two strains of this virus has been the virus in its present form will be useful as a completely sequenced . At Davis , for exam - recombinant DNA vector . However , this vi - ple , an isolate has been found to have 8,031 Small , ntergen , c rus will probably play an important role in reg > on pairs of nucleotides in its circular chromo - defining the biological activity of those se - some . Nucleotides make up the language Physical map of circular chromosome of quences involved in replication and expres - cauliflowermosaic virus . Genes defined by with which genetic information is expressed . sion of DNA in plants . by nucleotide sequence are indicated of nucleotides and other infor - This sequence arrowed lines I to VI . Box indicates naturally Robert J . Shepherd , Professor , and Stephen D . mation have been used to construct a physical occurring deletion of most of region I1 Daubert , Postdoctoral Research Associate , Plant map of the virus chromosome ( see diagram ) . ( strain CM4 - 184 ) . Open triangles indicate Pathology , U.C . , Davis ; and Richard C . Gard - ner , Principal Scientist , Calgene , Inc . , Davis . three single - stranded interruptions . Of the half - dozen genes of this simple virus , 16 CALIFORNIA AGRICULTURE , AUGUST 1982