Minisymposium 19: Gene regulation
Abs #
34001: Protein Kinase SNF1 Acts Upstream of A MYB Protein in the Sugar Signal Transduction Pathway in Plants
|
|
Presenter: |
Yu, Su-May |
Authors | Lu, Chung-An (A) Lin, Tse-Cheng (A) Lee, Kuo-Wei (A) Ho, Shin-Lon (A) Huang, Li-fen (A) Yu, Su-May (A) | | Affiliations: |
(A): Institute of Molecular Biology, Academia Sinica, Taipei, Taiwan, R.O.C.
|
|
|
In plants, sugars not only serve as metabolic resources and structural constituents of cells but also have hormone-like regulatory activities. Sugars modulate nearly all fundamental processes throughout the entire life cycle of plants, by regulating gene expression involved in diverse metabolic pathways and cellular functions. The detailed mechanism that connects sensing of sugars, transmission of sugar signals, and regulation of gene transcription is mostly unclear.
ƒÑα-Amylase is essential for hydrolysis of seed starch into sugars to sustain respiratory metabolism and growth and development of seedlings during germination of cereal grains. In germinating rice and barley embryos and cultured rice suspension cells, expression of α-amylase genes is activated by sugar starvation and repressed by sugar provision.ƒnƒn αAmy3 is the most abundantly expressed α-amylase gene in sucrose-starved rice suspension cells, and is also the earliest expressed α-amylase gene in germinating rice embryos. A sugar response sequence (SRS) in the αAmy3 promoter, which contains three motifs: GC box, G box, and TATCCA element (TA box), is essential for high level sugar starvation-induced promoter activity in rice cells. A MYB protein, OsMYBS1, binds specifically to the TA box both in vivo and in vitro, and functions as a transcriptional activator for sugar starvation induced SRS activity.
In yeast, SNF1 kinase is considered as a metabolic sensor that monitors cellular glucose status, and is required for derepression of nearly all glucose-repressed genes. We are interested in exploring the function of SNF1 in plants. The yeast SNF1 complex consists of one catalytic activating subunit (Snf1) and two regulatory subunits (Snf4 and Sip1/Sip2/Gal83). In the present study, we isolated genes encoding the rice Snf1 homolog (OsSnf1). OsSnf1 is structurally and functionally conserved as its yeast homolog. Function of OsSnf1 was further studied by transient expression assays in rice embryos. OsSnf1 also releases sugar repression of SRS activity specifically through the TA box, and acts upstream of OsMYBS in sugar derepression of SRS. This study demonstrates that OsSnf1 plays a key role in carbohydrate metabolism in plants, by regulating downstream gene expression through a mechanism unique for plants. For the first time, a component in the sugar signal transduction pathway is connected to a transcription factor for sugar regulation of transcription in plants.
