Abstract
The tie-dyed1 (tdy1) mutant of maize (Zea mays) produces chlorotic, anthocyanin-accumulating regions in leaves due to the hyperaccumulation of carbohydrates. Based on the nonclonal pattern, we propose that the accumulation of sucrose (Suc) or another sugar induces the tdy1 phenotype. The boundaries of regions expressing the tdy1 phenotype frequently occur at lateral veins. This suggests that lateral veins act to limit the expansion of tdy1 phenotypic regions by transporting Suc out of the tissue. Double mutant studies between tdy1 and chloroplast-impaired mutants demonstrate that functional chloroplasts are needed to generate the Suc that induces the tdy1 phenotype. However, we also found that albino cells can express the tdy1 phenotype and overaccumulate Suc imported from neighboring green tissues. To characterize the site and mode of action of Tdy1, we performed a clonal mosaic analysis. In the transverse dimension, we localized the function of Tdy1 to the innermost leaf layer. Additionally, we determined that if this layer lacks Tdy1, Suc can accumulate, move into adjacent genetically wild-type layers, and induce tdy1 phenotypic expression. In the lateral dimension, we observed that a tdy1 phenotypic region did not reach the mosaic sector boundary, suggesting that wild-type Tdy1 acts non-cell autonomously and exerts a short-range compensatory effect on neighboring mutant tissue. A model proposing that Tdy1 functions in the vasculature to sense high concentrations of sugar, up-regulate Suc transport into veins, and promote tissue differentiation and function is discussed.
Highlights
The tie-dyed1 mutant of maize (Zea mays) produces chlorotic, anthocyanin-accumulating regions in leaves due to the hyperaccumulation of carbohydrates
If the Tdy1 gene acts cell autonomously, tdy1 phenotypic regions should form in the albino mutant sectors and extend to the border of green, wild-type tissue
If Tdy1 functions completely noncell autonomously, no tdy1 regions should occur in the white tissue, as Tdy1 function in neighboring wildtype cells would generate a mobile product that can complement the mutation in albino tissues
Summary
Tdy Region Boundaries Are Often Delineated by Lateral Veins tdy leaves exhibit a nonclonal pattern of chlorotic regions that accumulate carbohydrates A tdy region spread into adjacent Yg-str* palegreen mutant tissue (Fig. 4, B, arrows, and L), and the chlorophyll autofluorescence seen in pale-green mutant tissue was reduced (compare Fig. 4, J and M) These tissues expressed anthocyanin and exhibited starch accumulation in mesophyll cells similar to tdy. We analyzed white tissues marked by anthocyanin pigmentation to determine which cell layers lacked wild-type Tdy function and thereby resulted in expression of the tdy phenotype (Fig. 5B) In this experiment, we observed tdy regions within albino tissue W14 tdy1/2 albino sectors containing tdy phenotypic regions marked by anthocyanin lacked chlorophyll (Fig. 7, I and J) and accumulated starch in both mesophyll and bundle sheath cells (Fig. 7, K and L) These results show aneuploid leaf sectors express the tdy phenotype. Tdy acts non-cell autonomously over a limited distance
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