Genetic and histological analysis of Rolled
--Nelson, J, Lane, B, Freeling, M

Rolled (Rld) is a semi-dominant mutation in which dorsiventral (adaxial-abaxial) polarity is switched with the morphological outcome of leaves which roll inward, toward the midvein. These adaxial-abaxial switches involve the epidermal and ground tissues, excluding the vascular bundles which retain wildtype polarity. The extent of the epidermal phenotype includes presence of ligule tissue on the abaxial blade/sheath boundary, switching of abaxial and adaxial epidermal cell types: the expression of characteristically adaxial cell types such as macrohairs and bulliform cells on the abaxial surface, and the lack of them on the adaxial surface. The internal phenes of the Rolled mutation include abnormal patterning of the hypodermal schlerenchyma which might create or reinforce a structural imbalance resulting in the curvature of the leaf blade. In addition, a disruption in the formation of transverse and intermediate veins in regions of the blade and sheath is frequently seen; this results in a pale stripe at the blade/sheath boundary.

Mosaic analysis was done to identify the focus of action of the mutant gene product ROLLED. We used the Rld1-0 allele. This mosaic analysis of ROLLED was set up by crossing pollen from white luteus4 (wlu4) heterozygotes onto Rld/+ ears. The progeny of this cross were imbibed and then exposed to x-irradiation. This generated white wild-type sectors (wlu,+/--)in green Rolled (wlu,+/+,Rld) background. Preliminary results of mosaic mapping suggest that ROLLED acting in the epidermis only is sufficient to switch the dorsiventral polarity.

Mosaic Analysis. Transverse sections of leaves of wlu4, rld1+/Wlu+, Rld1-O genotype in A, B and C. White sectors indicate removal of the dominant mutant allele Rld1-O from partiicular tissue layers of leaf. A) Leaf with no white sectors. Inset tissue-layer drawing shows this. Note the inversion of the abaxial and adaxial epidermal layers, characteristic of Rld mutants. B) White sector, indicated by arrow-heads, marks the loss of Rld1-O. Close examination showed epidermis guard cells were still green, as shown by inset. This sector had typical Rld1-O polarity. C) Rld1-O.

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