FURTHER CHARACTERIZATION OF EXPRESSION OF AUXIN-INDUCED GENES IN TOBACCO (NICOTIANA-TABACUM) CELL-SUSPENSION CULTURES

We have described the modulation of four auxin-regulated genes during the growth cycle of suspension-cultured tobacco (Nicotiana tabacum [L. ] var White Burley) cells. The genes were transiently expressed 2 to 8 h after transfer of stationary phase cells to fresh medium, during th e transition from the quiescent phase of cells leaving the mitotic cyc le to the synthesis phase of the cell cycle. After this transient indu ction, the cells showed a decreased sensitivity to auxin. Although the expression pattern suggests that induction of these genes might be im portant for cell division, over-production of antisense mRNA for one o f these genes (pCNT103) did not influence cell division in transgenic tobacco cells. Furthermore, stimuli such as salicylic acid were capabl e of inducing gene expression but were unable to restore cell division . Although these data do not conclusively exclude a role for these gen es in cell division, their significance in this process is discussed i n view of their homology with other auxin-induced genes and in view of the specificity of hormone-induced early responses.