USDA-ARS, Plant Gene Expression Center
University of Illinois
Wab (Wavy auricles in blades), a dominant leaf mutation located on chromosome 2L
--Hake, S, Hester, H, Wassom, J, Widholm, J, Rocheford, T

We have characterized and mapped a new dominant leaf mutation that arose spontaneously in an in vitro androgenesis tissue culture derived line. Normal maize leaves have a blade portion that is broad and flat, a sheath portion that wraps around the culm, and a ligule and auricle located at the junction of blade and sheath. The ligule is an epidermally-derived fringe and auricles are the two pale green, wedge-shaped tissues located just above the ligule. The Wab (Wavy auricles in blade) mutation is characterized by auricle tissue that is found in the blade portion of the leaf. Most often the extra auricle is adjacent to the normal auricle, spreading distally, other times the extra auricle is surrounded by normal leaf blade tissue (Figure 1). Wab leaf blades have a more pronounced horizontal posture, possibly due to the extra auricle tissue. Leaf blades are also narrower. We measured leaf widths for 40 mutants and normal siblings in a population that was back-crossed to B73 three times. Wab leaves #13 and #14 (counting from the base of the plant) were 59% and 57% of the wild-type width. We have also noted that there are one to three more leaves in Wab mutants that normal siblings. Occasionally, leaves are found that are very narrow and have no ligule at all, otherwise the normal ligule is not affected.

The phenotype is fully penetrant and severe in B73. The phenotype is less severe in A619 and Mo17. A preliminary examination of a small population suggests that homozygotes are not obviously different than heterozygotes. The phenotype is most striking in adult plants, but can be scored as early as leaf #4 by the presence of slightly translucent margins and narrower leaves.

We crossed Wab mutants into a liguleless1 (lg1) mutant background to determine the effect on the ectopic auricle. lg1 mutants lack a ligule and auricle, and have very upright leaves (Sylvester et al., Development 110:985 1990). The normal and ectopic auricle of Wab mutants disappeared in the lg1 background and the leaves were more narrow than the leaves of lg1 single mutants (Figure 1). The margins of the Wab;lg1 mutant at the sheath/blade border were membranous.

We used waxy translocation stocks to map the mutation to chromosome 2. Linkage was found with both T2-9b and T2-9d. Further mapping of a population back-crossed twice into B73 showed tight linkage with umc98a. One recombinant was found in a total of 32 giving an approximate map position of 3 cM from umc98a.

Figure 1. A. Wab and a normal sibling are compared in a colored background in which the auricles are white and the blade and sheath red. The auricle tissue extends up the leaf margin in the Wab individual (a = auricle). B. Adaxial surface of half leaves of lg1, Wab, and a lg1;Wab double mutant are compared. Compare the leaf widths (arrows). C. Hand-sections of normal and Wab leaves were examined under the fluorescent scope. Portions of the Wab blade resemble the normal auricle in histology.

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