A genetic study on the activiation of quiescent Uq transposable elements in Zea mays L.
The standard a-ruq allele reports the activity of the Uq transposable element in the form of color spots or sectors of color spots in otherwise colorless aleurone tissue. As reported by this a-ruq, genomes of four maize inbred lines (C123, C103, B70 and 187-2) lack an active Uq element. However, these genomes contain quiescent Uq sequences that randomly and infrequently become activated;Spontaneous activation of quiescent Uq sequences during development of a-ruq/a-ruq/a-ruq endosperm results in sectors of Uq-a-ruq spotting in otherwise colorless aleurone tissue;Spontaneous germinal activation (at a rate of about 2 x 10[superscript]-4) of quiescent Uq sequences produces individual fully-spotted exceptional kernels of a-ruq/a-ruq/a-ruq genotype. Their spotting patterns differ from the pattern of the standard Uql-a-ruq spotting. Five new Uq elements, designated Uq2, Uq3, Uq4, Uq5, and Uq6, respectively, have been isolated. The genetic authenticity of these new Uq elements has been established;These five new Uq elements are independent of Uq1 and are clustered on one linkage group. Uq2 is allelic to Uq4, Uq3 is allelic to Uq5, whereas Uq6 is linked to both allelic pairs;Another quiescent Uq element has been activated in a maize plant upon treatment with 5-aza-2[superscript]'-deoxycytidine. This Uq consegregates with a coinduced miniature mutant that is found to be independent of mn1, mn2, and mn7690. The cosegregating genetic unit, designated Mn::Uq, acts dominantly and is not male transmissable. An in vitro pollen germination study shows that Mn::Uq pollen does not germinate, thereby causing this male nontransmissibility. Definitive genetic proof for the Uq nature of the mutant is given by the fact that a reconstitution testcross between a°/a°, Mn::Uq/+ and the a-ruq/a-ruq tester produces 50% spotted miniature and 50% colorless normal progeny;The Mn::Uq mutant does not transactivate the c-ruq65 and c-ruq67 alleles, two other Uq1-responding reporter alleles. In addition, Ug3, Ug4, and Ug5 transactivate the c-ruq alleles in a much weaker fashion than they transactivate a-ruq. These results suggest that structural differences may exist between these ruq receptor elements at the a-ruq and c-ruq alleles.