Genetic mapping of expressed sequence tag polymorphism (ESTP) markers in loblolly pine (Pinus taeda L.)

The development and mapping of genetic markers based upon expressed sequenc e tag polymorphisms (ESTPs) in loblolly pine (Pinus taeda L.) are reported. The new markers were generated by PCR-amplification of loblolly pine genom ic DNAs with primers designed from sequenced cDNAs. The cDNA libraries were constructed from RNAs expressed in the needles of loblolly pine seedlings or in the xylem from young trees. DNA polymorphisms were identified by anal yzing the amplified products for differences in fragment size or restrictio n sites, or by examining mobility differences using denaturing gradient gel electrophoresis (DGGE). DGGE revealed more DNA polymorphisms than the othe r two methods. Fifty six ESTPs were mapped using either of two mapping popu lations and positioned onto a loblolly pine consensus genetic map. Unlike m any other markers commonly used in forestry, ESTPs can be used as orthologo us markers for comparative mapping, to map genes of known function, or to i dentify candidate genes affecting important traits in loblolly pine.