EXCEPTIONAL SEGREGATION OF A SELECTABLE MARKER (KAN(R)) IN ARABIDOPSIS IDENTIFIES GENES IMPORTANT FOR GAMETOPHYTIC GROWTH AND DEVELOPMENT

Genes transformed into plants are usually inherited in a regular Mende lian manner. There are, however, transformants in which the selectable trait fails to segregate as expected. Genetic analysis of the kanamyc in-resistance (Kan(R)) trait in >900 independent transformants of Arab idopsis revealed that 9% produced progeny families with an enormous de ficiency of Kan(R) individuals. Self-pollination of individual Kan(R) plants from these families revealed lines that continued to segregate for a deficiency of Kan(R) seedlings. In subsequent generations, the s egregation ratio in these families stabilized at similar to 1 Kan(R): 3 Kan(S). Molecular analyses showed that the deficiency of Kan(R) indi viduals reflected the complete absence of the introduced DNA. Reciproc al backcrosses to untransformed plants showed unequal transmission of the Kan(R) trait through the gametes in these exceptional lines. In fi ve cases, this was primarily a failure of transmission through the mic rogametophyte (pollen) and in the other two cases, primarily a failure of transmission through the megagametophyte (embryo sac or egg). The number of seeds per silique was reduced by 50% in the latter two lines . We conclude that our exceptional transformants contain T-DNA inserti ons that delete or disrupt genes essential for gametophytic growth and development.