FEATURES OF THE HMG-1 SUBFAMILY OF GENES ENCODING HMG-COA REDUCTASE IN POTATO

3-Hydroxy-3-methylglutaryl coenzyme A reductase (HMGR) catalyzes a key step in isoprenoid metabolism leading to a range of compounds that ar e important for the growth, development and health of the plant. We ha ve isolated 7 classes of genomic clones encoding HMGR from a potato ge nomic library. Comparison of nucleic acid sequences reveals a high deg ree of identity between all seven classes of clones and the potato hmg 1 gene described by Choi et al. (Plant Cell 4: 1333, 1992), indicatin g that all are members of the same subfamily in potato. A representati ve member (hmg 1.2) of the most abundant class of genomic clones was s elected for further characterization. Transgenic tobacco and potato co ntaining the beta-glucuronidase (GUS) reporter gene under the control of the hmg 1.2 promoter expressed GUS activity constitutively at a low level in many plant tissues. High levels of GUS activity were observe d only in the pollen. GUS assays of isolated pollen, correlations of G US activity with the HMGR activity of anthers, hmg 1.2 promoter deleti on studies, and segregation analysis of the expression of hmg 1.2::GUS among the R(2) pollen of R(1) progeny plants demonstrated that the hm g 1.2 promoter controls pollen expression.