EEB340 Lecture 10.docx

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10 Apr 2012
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Lecture 10: Evolution of Leaves
Evolution of Leaves
Meristem activity/transcription factors
Leaf primordial/transcription factors
Marginal activity/transcription factors
Adaxialization/Abaxialization of leaves/transcription factors
Auxin and leaf initiation and vascularization
- Flowering plants
o Shoot apical meristem: multiple initials
o Some will have multiple layers with similar characteristics
o Shoot apical meristem is indeterminant
o Leaves develop from peripheral zone
o Central zone is region of stem cells source of cells for the rest of the plant
o Cells of the peripheral zone have higher division rates than those of the
central zone
o Central zone cells larger than peripheral cells
Have larger vacuoles peripheral dividing faster so smaller vacuoles
o Rib meristem cell division rate intermediate between central and peripheral
zone cells
Transcription Factors
- Knox Genes
o Increased expression in central zone
o Decreased expression in peripheral zone with initiation of leaf primordia
o Responsible for maintaining cells in the central zone in an indeterminent
state
- WUS: increase expression in central zone
o Decreased expression in peripheral zone with leaf primordial
o Keeps central zones cells actively dividing and in undifferentiated state
(similar to Knox)
- Abaxial side bottom
- Adaxial side top
- HD-ZIP II genes are important in promoting adaxialization of the leaf
- KANADI genes promote abaxial identity
- Together these two work antagonistically with each other
- When leaves are initiated, there is a down regulation of the WUS and Knox genes
both promote indeterminent cells in the margin
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