MYB Family Transcription Factors

Jonathan Russell

Rena Schweizer

Mike Douglas

What is a Transcription Factor?

• Transcription factor –

any protein other than RNA

Polymerase that is required for

transcription

MYB Family

• Myeloblast ---> MYB (came from first identified MYB which was in an avian oncogene)

• 203 identified MYB-family transcription factors

• Found in Eukaryotes

Our Genes Within the Myb Family

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Mike

Jonathan

Jonathan

Mike

RenaRena

MYBFAMILY

PHYLOGENY

• What is the Structure

and Function of MYBs?

Jonathan’s Gene

Jonathan’s GeneEmily’s Gene

What is the Structure of MYB Proteins?

• All share a conserved MYB DNA-Binding Domain

– Up to three imperfect repeats (Helix-Turn-Helix structure) of ~53 AA each

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–Three regularly spaced tryptophan residues

–R1, R2, R3 repeats

–Subfamilies are classified by number of adjacent repeats (MYBR1, R2R3-type MYB, MYB3)

What Motifs Do Mybs Employ?

• Helix-turn-Helix structures are crucial to sequence specificity

• HTH intercalates in major groove

• Recognition by C-terminal helix

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MYB Structure: R2R3 Sub Family

• Largest family characterized in plants

• Both R2 and R3 required for sequence-specific binding

• Some redundancy of amino acid sequence, but flexibility in recognition

What are the functions of Plant MYB Proteins?

• Wide diversity of functions

• By no means fully characterized

• In general: regulate many aspects of plant metabolism and development

• But…– Some bind telomeric sequences, structural– Some are clearly transcription factors

(from circadian clock to root hair formation)

Proposed Plant MYB Functions

Vertebrates• Cellular proliferation• Expressed in actively dividing cells before

differentiationPlants• Control of secondary metabolism• Regulation of cell morphogenesis• Serving in signal transduction pathways

responding to plant growth regulators

Specific MYB Functions

Controlling Secondary Metabolism

• Phenylpropanoid metabolism (modifications of compounds derrived from phenylalinine)

• One branch resposible for the production of anthocyanins (major group of plant pigments)

Regulating Cellular Morphogenesis

• In petunia, essential for developing the conical form of petal epidermal cells

• In Arabidopsis, essential for differentiation of hair cells in leaf and stem

Signal Transduction Pathways

• Hormonal responses during seed development and germination

• In Arabidopsis and maize, activate genes to respond to dehydration and salt stress

For all categories, variations across plant species

The Future of MYB Experiments

• In order to characterize each MYB gene, mutation studies need to be performed

• This involves: knocking out specific genes and looking for resulting phenotypes…

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