Regulating development in
plants
Homeotic mutation has elucidated aspects of plant development
The outstanding model for plant genetics is Arabidopsis thaliana, this was the first plant to
have its genome sequenced, its small, easy to grow in large numbers, can be self or cross
fertilised, it’s a geneticist’s wet dream
Antirrhinum majus(snapdragon) is a plant that has been used for studying the genetics of
floral development, it’s good for comparison with Arabidopsis because Arabidopsis has
radially symmetrical flowers where as antirrhinum has bilaterally symmetrical flowers
Mutants in antirrhinum have been used to identify genes specifying the axes of symmetry in
floral development
Ariel parts of plant develop from the shoot apical meristem
The meristem is continually mitotically active, during cell divisions continually renew the
apex which show intermediate growth.
Cells around the meristem differentiate to produce leaf primordia
Leaf primordia shows determinate growth= they won’t produce any further structures
Flowering in plants occurs as a result of a change in the commitment of cells in the root
meristem, from vegetative to reproductive structures. Usually triggered by environmental
stimuli
If the shoot terminates then the meristem Is reprogrammed to become a floral meristem
Floral meristems are determinate, they generate floral primordia that represents the
terminal differentiation
Mutation in snapdragon call floricaula cause a homoeotic transformation in the meristem
resulting in highly branched and complex inflorescences that don’t produce determinate
flowers
The homologous gene in Arabidopsis mutates to give the same phenotype called “leafy”
The leafy/floricaula gene encodes a transcription factor that’s need to initiate the expression
of the gene responsible for floral development, so when not, functional can’t produce floral
organs
How are floral organs specified?
established as a result of the interpretation of positional information in the shoot tip
flowers comprise 4 concentric whorls of organs: whorl 1- sepals, whorl 2- petals, whorl 3-
stamens and whorl 4- carpel (female structures)
3 classes of mutation change the fate of an adjacent pair of whorls
Class A: mutation results in the replacement of sepals and petals by carpels and stamens
Class B: mutation results in replacement of petals and stamens by sepals and carpels
Class C: mutation results in loss of stamens and carpels, and the formation of extra whorls of
sepals and petals
Based on these phenotypes it was possible to develop a model for how genetic
determination of floral anatomy was achieved= ABC model
Rules of ABC model:
1. There are 3 classes of homeotic gene, A, B and C
2. Each class expressed in 2 adjacent whirls of the floral meristem
plants
Homeotic mutation has elucidated aspects of plant development
The outstanding model for plant genetics is Arabidopsis thaliana, this was the first plant to
have its genome sequenced, its small, easy to grow in large numbers, can be self or cross
fertilised, it’s a geneticist’s wet dream
Antirrhinum majus(snapdragon) is a plant that has been used for studying the genetics of
floral development, it’s good for comparison with Arabidopsis because Arabidopsis has
radially symmetrical flowers where as antirrhinum has bilaterally symmetrical flowers
Mutants in antirrhinum have been used to identify genes specifying the axes of symmetry in
floral development
Ariel parts of plant develop from the shoot apical meristem
The meristem is continually mitotically active, during cell divisions continually renew the
apex which show intermediate growth.
Cells around the meristem differentiate to produce leaf primordia
Leaf primordia shows determinate growth= they won’t produce any further structures
Flowering in plants occurs as a result of a change in the commitment of cells in the root
meristem, from vegetative to reproductive structures. Usually triggered by environmental
stimuli
If the shoot terminates then the meristem Is reprogrammed to become a floral meristem
Floral meristems are determinate, they generate floral primordia that represents the
terminal differentiation
Mutation in snapdragon call floricaula cause a homoeotic transformation in the meristem
resulting in highly branched and complex inflorescences that don’t produce determinate
flowers
The homologous gene in Arabidopsis mutates to give the same phenotype called “leafy”
The leafy/floricaula gene encodes a transcription factor that’s need to initiate the expression
of the gene responsible for floral development, so when not, functional can’t produce floral
organs
How are floral organs specified?
established as a result of the interpretation of positional information in the shoot tip
flowers comprise 4 concentric whorls of organs: whorl 1- sepals, whorl 2- petals, whorl 3-
stamens and whorl 4- carpel (female structures)
3 classes of mutation change the fate of an adjacent pair of whorls
Class A: mutation results in the replacement of sepals and petals by carpels and stamens
Class B: mutation results in replacement of petals and stamens by sepals and carpels
Class C: mutation results in loss of stamens and carpels, and the formation of extra whorls of
sepals and petals
Based on these phenotypes it was possible to develop a model for how genetic
determination of floral anatomy was achieved= ABC model
Rules of ABC model:
1. There are 3 classes of homeotic gene, A, B and C
2. Each class expressed in 2 adjacent whirls of the floral meristem
