Identification of new male sterile-silky gene(s)
--Pamela Close* and Steve Briggs
*Iowa State University

The silky (si1 or ms-si) mutation was first reported in 1933 by A. C. Fraser, AC. Ears are phenotypically normal except for the presence of up to three additional silks around the base of each kernel. These silks persist long after fertilization of the ear. The additional silks arise from the tips of three "paddle-like" protuberances which develop in a whorl around the kernel. These "paddles" are carpel-like in appearance. The whorl is within the first flower of the spikelet and appears to be at the position where stamens would develop if maize produced a perfect flower. Silks are present on the tassels, which are typically male-sterile. No seed is produced by the tassel.

We have observed at least two new silky mutations within our active Mutator lines. These mutants are of independent origin and are phenotypically indistinguishable from the si1 (ms-si) tester stock obtained from the Maize Cooperation Stock Center. Allelism tests repeated over two seasons indicate that neither of these two mutations is allelic to si1. We are currently testing whether they are allelic to each other. Expression of both ear and tassel phenotype of one of the new silky mutations varies considerably with genetic background.

The new silky mutations are currently being screened for co-segregating Mutator-containing restriction fragments.

To investigate gene interactions, we are making crosses to combine the new silky mutations with other mutations affecting the development of the maize flower. Since gene duplication is common in maize, si1 and the new silky mutation(s) may encode the same function. Alternatively, two genes have been identified in Arabidopsis (apetala-3 and pistillata) which cause a similar transformation of the stamen whorl to carpel. It is possible that si1 and the new silky mutations may be functional homologs of these genes. 

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