Y1 gene expression in the endosperm and leaves
--Brent Buckner and Claravon Mathews
The Y1 gene is involved in the biosynthesis of carotenoids in maize. The endosperm of a kernel that contains one or more dominant Y1 alleles is yellow due to the accumulation of carotenoids including y1 allele is white or pale-yellow (depending on the genetic background of the plant) and contains very low levels of these carotenoids. Carotenoid levels are essentially equal in the leaves of plants that are homozygous for the standard Y1 or y1 alleles. However, plants that are homozygous for certain alleles of y1 contain reduced amounts of carotenoids in their leaves, as well as in their endosperm. The reduction of carotenoids in the leaf results in a light-green phenotype (referred to as pastel) due to the photooxidation of chlorophyll. Therefore, the product of the Y1 gene appears to be involved in the biosynthesis of carotenoids in the leaf, as well as in the endosperm.
To understand how the Y1 gene is involved in carotenoid biosynthesis in maize endosperm and leaves, we are analyzing the expression of this gene in these tissues. We have identified a 1.8Kb Y1 mRNA in the endosperm of maize kernels that were homozygous for the dominant Y1 allele, while no Y1 mRNA was detected in the endosperm of kernels that were homozygous for the recessive allele. In addition, Y1 mRNA was detected in the leaves of seedlings that were homozygous for either the recessive or dominant alleles, however, the Y1 mRNA transcript from the dominant allele is 1.8Kb (as was found in the endosperm), while the Y1 mRNA transcript from the recessive allele was 2.0Kb. Interestingly, seedlings homozygous for a Mu3-induced temperature-sensitive pastel allele of y1 contain a 1.7Kb Y1 mRNA transcript. Therefore, the Y1 gene appears to be regulated in a tissue specific manner and different alleles of y1 code for different length Y1 mRNA transcripts.
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