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作者 Ma, Yi
書名 Characterization and cloning of tie-dyed1, a novel gene regulating carbohydrate partitioning in maize leaves
國際標準書號 9781124084268
book jacket
說明 171 p
附註 Source: Dissertation Abstracts International, Volume: 71-07, Section: B, page: 4102
Adviser: David Braun
Thesis (Ph.D.)--The Pennsylvania State University, 2008
Acquisition of cell identity requires communication among neighboring cells. To dissect the genetic pathways regulating cell signaling in later leaf development, a screen was performed to identify mutants with sectors that violate cell lineage boundaries in maize (Zea mays) leaves. We identified a recessive mutant, tie-dyed1 ( tdy1), which develops stable, nonclonal variegated yellow and green leaf sectors. Sector formation requires high light, occurs during a limited developmental time, and is restricted to leaf blade tissue. Yellow tdy1 sectors accumulate excess soluble sugars and starch, whereas green sectors appear unaffected. Significantly, starch accumulation precedes chlorosis in cells that will become a yellow sector. Retention of carbohydrates in tdy1 leaves is associated with a delay in reproductive maturity, decreased stature, and reduced yield. To explain the tdy1 sectoring pattern, we propose a threshold model that incorporates the light requirement and the hyperaccumulation of photoassimilates
tdy1 and sucrose export defective1 (sxd1) are the only recessive mutants known with nonclonal chlorotic leaf sectors that hyperaccumulate starch and soluble sugars. Based on their similar mutant phenotypes, we investigated whether tdy1 and sxd1 function in the same pathway. Using aniline blue staining for callose and TEM to inspect plasmodesmatal ultrastructure, we determined that tdy1 does not have any physical blockage or alteration along the symplastic transport pathway as found in sxd1 mutants. To test whether the two genes function in the same genetic pathway, we constructed F2 families segregating both mutations. Double mutant plants showed an additive interaction for growth related phenotypes and soluble sugar accumulation, and expressed the leaf variegation pattern of both single mutants indicating that Tdy1 and Sxd1 act in separate genetic pathways. Although sxd1 mutants lack tocopherols, we determined that tdy1 mutants have wild type tocopherol levels, indicating that Tdy1 does not function in the same biochemical pathway as Sxd1. From these and other data we conclude that Tdy1 and Sxd1 function independently to regulate carbon export
To characterize Tdy1's function at the molecular and cellular levels, Tdy1 was cloned using transposon-tagging. Tdy1 encodes a novel protein highly conserved in grasses with orthologs in rice, sorghum and sugarcane. Though no ortholog was found in dicot plants, two stretches of amino acid sequences were found to have similarities to TDY1, which implies the function of TDY1 may be conserved in higher plants. In addition, maize genomic DNA Southern blotting revealed a duplicate gene for Tdy1, and multiple related sequences were discovered by BAC filter hybridization suggesting that Tdy1 belongs to a small gene family. It is possible that the closest duplicate gene partially compensates for Tdy1 function so that the tdy1 mutant does not show uniform chlorosis in its leaves. Semi-quantitative RT-PCR showed that Tdy1 is expressed in both source leaves and young sink tissues. Furthermore, in situ hybridization localized Tdy1 RNA in phloem cells, supporting a potential function in phloem transport. As sucrose transporters are involved in phloem loading, their expression patterns were examined and overlapping expression was found for ZmSUT2 and ZmSUT4. The results suggest that Tdy1 may function in regulating phloem transport of sucrose in maize plants
School code: 0176
Host Item Dissertation Abstracts International 71-07B
主題 Biology, Plant Physiology
0817
Alt Author The Pennsylvania State University
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