--Scott Poethig

Last year I reported that hyperploidy for TB-1La suppressed tiller formation in Tp1/+ plants. This effect may be due to an increase in the dose of the wild type teosinte branched allele (which is located at the distal end of 1L) because recessive mutations of this locus interact synergistically with Tp1 to enhance tiller production. In order to test this hypothesis further, Tp1/+ plants carrying a duplication for the region around the tb locus were created using an overlapping translocation stock originally generated by Jim Birchler. This stock carries the translocations T1-3(5267) and T1-3(5242), and duplicates a region representing 18% of 1L. The results presented in Table 1 demonstrate that this duplication has a significant suppressive effect on tiller formation in Tp1/+ plants. This result is therefore consistent with the hypothesis that the dosage effect of 1L is a function of an increase in the dose of the wild type tb allele. Conclusive proof of this hypothesis would be provided by the phenotypic equivalence of +/+/tb; Tp1/+ and +/+; Tp1/+ plants. These genotypes are currently being constructed.

Table 1: The effect of a 1L duplication (.72--.90) on the expression of Tp1.
 

Families	# of tillers
	+/+; Tp1/+	+/+/+; Tp1/+
D926A	3.6 (N=8)	2.2 (N=10)
D926B	1.8 (N=9)	0.6 (N=10)
D926C	2.9 (N=10)	1.0 (N=4)
D926D	3.5 (N=11)	0.6 (N=7)
Total	3.0 ± 0.25	1.2 ± 0.22

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