Some thoughts on nuclear genes affecting plastid development

--Philip S. Stinard

In the course of our studies of the Mutator transposable element system, we have had the occasion to observe many different endosperm and seedling mutants. The mutants conditioning etched/sugary endosperm and seedlings with reduced chlorophyll content make up a class of frequently observed mutants that has received relatively little attention. Mutants fitting into this class include et, dek5, dek7, w2 (dek21), and cp2. All of these mutants have alleles that produce mosaicism for aleurone color in a colored aleurone background; all have etched or pitted endosperm. The mutants et, dek5, dek7, and cp2 have alleles producing a sugary/shrunken endosperm phenotype. The mutant et produces virescent seedlings; the mutants dek5, dek7, and cp2 produce striate seedlings (white or pale green with green stripes), and w2 produces white seedlings (yellow seedlings with homozygous l1; the interaction of l1 with the other mutants in this class is not known).

Previously reported studies of et (Ramesh and Reddy, MNL 59:52) and w2 (Han and Coe, MNL 64:45-46) have indicated that seedling plastids are affected in both mutants (plastid membrane structure in et, amount of plastid DNA in w2). If the abnormal seedling phenotypes associated with this class of mutants are due to plastid defects, then perhaps the abnormal endosperm phenotypes are due to plastid (amyloplast) defects as well. If this is the case, then these nuclear gene mutations may be disrupting biochemical pathways involved in general plastid structure or development. Studies of these mutants may aid in the elucidation of these pathways.

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