We profiled soybean and Arabidopsis methylomes from the globular stage through dormancy and germination to understand the role of methylation in seed formation. CHH methylation increases significantly during development throughout the entire seed, targets primarily transposable elements (TEs), is maintained during endoreduplication, and drops precipitously within the germinating seedling. By contrast, no significant global changes in CG- and CHG-context methylation occur during the same developmental period. An Arabidopsis ddcc mutant lacking CHH and CHG methylation does not affect seed development, germination, or major patterns of gene expression, implying that CHH and CHG methylation does not play a significant role in seed development, or regulating seed gene activity. By contrast, over 100 TEs are transcriptionally de-repressed in ddcc seeds suggesting that the increase in CHH-context methylation may be a failsafe mechanism to reinforce transposon silencing. Many genes encoding important classes of seed proteins, such as storage proteins, oil biosynthesis enzymes, and transcription factors, reside in genomic regions devoid of methylation at any stage of seed development. Many other genes in these classes have similar methylation patterns whether the genes are active or repressed. Our results suggest that methylation does not play a significant role in regulating large numbers of genes important for programming seed development in both soybean and Arabidopsis. We conclude that understanding the mechanisms controlling seed development will require determining how cis-regulatory elements and their cognate transcription factors are organized in genetic regulatory networks.
We used laser capture microdissection (LCM) to isolate specific compartments, regions, tissues, and cell types from soybean and Arabidopsis seeds
at different stages of development – including the seed coat, endosperm, and embryo regions and organ systems. Microarray, Next-generation sequencing,
and qRT-PCR experiments were carried out in order to determine (1) the spectrum of genes that are active in different parts of seed during
development and (2) transcription factors and biological processes that partitioned within a seed playing important roles in seed differentiation
and/or function. Functional studies were also carried out in order to determine what role compartment and tissue-specific transcription factors
play in soybean seed development.
Utilizing a genomics approach, we profiled mRNAs active during Arabidopsis seed development using whole-genome Affymetrix GeneChips ATH1-121501. Specifically, we profiled mRNAs active during seed development at 24 hours post-fertilization, 7-8 days after pollination (DAP), 13-14 DAP, and 18-19 DAP. These gene sets were compared with those active in pre-fertilization ovules, seedlings 3 days after imbibition, leaves, roots, stems, and floral buds of the mature plant. Collectively, we have carried out whole-genome analysis of genes active during the entire Arabidopsis life cycle.
Our lab has utilized the SRB as a model system to identify genes and regulatory networks programming early embryo developmental
events using a genomic approach. Our long-term goal is to understand the region-specific differentiation processes that occur
during early embryo development and how genes are activated specifically in the suspensor and embryo proper. The SRB is unique in
this regard because of its giant seed and large embryo, permitting hand dissection of the embryo-proper and suspensor regions at
early developmental stages. Before the high-throughput sequencing era, total RNAs isolated from the hand-dissected suspensor and
embryo proper were used to construct cDNA libraries. The 5' ends of individual cDNA clones from each library were sequenced
using the Sanger sequencing method whereas random cDNA fragments were sequenced using the 454 sequencing technology.
~390,000 ESTs were identified and representing messages active 6-7 days after fertilization in different embryo regions of
the early embryo. We've also created a database where you can query your sequences against our Scarlet Runner Bean ESTs using
local BLAST tools. All of our EST sequences have been submitted to GenBank. Their accession numbers are: CA896559 to CA916678
and GD289845 to GD660862. You can access all of these sequences at NCBI.
Molecular and Genetic Dissection of Plant Development
My laboratory has been investigating the molecular processes controlling the development of specialized cells in higher plants. The major questions that I have addressed in my research are ....Read more
The Seed Institute was established in order to carry out basic research in seed biology with the objective of uncovering the genes and processes required to "make a seed." The long-range goal of the Seed Institute, in partnership with Ceres, is to use new insights obtained on the mechanisms that control seed formation to improve seeds in major crop plants....Read More
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