Gibberellin Biosynthesis in Maize-Chemistry, Biochemistry and Genetics

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WPC 2 B P Z Courier 10cpi #| x =V x 6 X @ 8 ; X @ Canon LBP-8III (Additional) CALB8IAD.PRS x @ 0J zX @ #| x 2 % B X g F ` Courier 10cpi Courier Footnote 16cpi . ? x x x , =V x 6 X @ 8 ; X @ + H H H , S , H 6 X @ ; @ t 7 } 3 J4 s @ u $ u $ t 7 } 3 O4 K ^_ZY X P C~ } X C~ YX P C~ X PSQRVW 8 W u a c e g i i = : W _^ZY X 9306597 ` ` Phinney Through the pioneering use of single gene mutants, the PI has defined most of the steps in the pathway for gibberellins ? biosynthesis in maize vegetative shoots. We have shown that GA 1 is the major gibberellin controlling stem elongation in maize and that geranylgeranylpyrophosphate (GGPP) is metabolized to ? x copalylpyrophosphate (CPP0, ent kaurene, GA 12 , and G 1 via the early 13 hydroxylation branch pathway. This proposal describes metabolic experiments that will establish five remaining steps in this branch pathway and locate the steps blocked by our d2 , d3 , and anl mutants. In addition, metabolic studies with five members of a ? ` second branch pathway from GA 12 (the early non 3,13 hydroxylation pathway) will assess the importance of this pathway in the control of GA dependent growth in maize. The results from the proposed metabolic studies will provide a detailed description of the gibberellin biosynthetic pathways for maize shoots and will provide a model for studies with other plants. A search for additional GA (dwarf) mutants will be continued: these mutants are being generated by transposon tagging using the maize transposable element Ac. The location of the genetic blocks for the new mutants will be determined form bioassays, qualitative analysis of endogenous givverellins, and metabolic studies. An exciting and novel aspect of this proposal comes from the availability of transposon tagged dwarf mutants. The approach provides a convenient method for cloning specific genes for GA biosynthesis. These clones will be used in conjunction with conventional methods to isolate the enzymes that control specific steps in the biosynthetic pathway. %%% The objective of the research is to understand shoot elongation controlled by the class of plant hormones, the gibberellins (GAs). The strategy is to (i) identify the genes and the gene products for these steps in the pathway, and (iii) analyze the enzymes controlling these steps, and thereby provide information for the future manipulation of plant growth. ***