Floral development and maturation, Study notes of Genetics

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FLORAL

DEVELOPMEN

T

INTRODUCTION

 Floral development involves firstly the transition of shoot apical meristem into and then the floral meristem undergoes changes to form flower.  Flower is considered as a modified shoot.Many genes are involved in the conversion of vegetative meristem to floral meristem.  Floral meristem initiate 4 different types of floral organs: sepals,petals,stamens & carpels. These

Genes that regulate

floral development in

Arabidopsis thaliana

2 major categories

1. Floral meristem identity genes : activity of these genes in immature primordia formed at the flanks of the shoot apical meristem, results in the transition to form the floral meristem.  AGAMOUS LIKE-20(AGL 20):master switch initiates floral development  Leafy( LFY) : necessary for the conversion of inflorescence meristem to floral meristem.It defines petals and stamens.  APETALA1 (AP1)AG: involve in sepal and petal development. Once activated AGL20 triggers the expression of LFY,LFY turns on expression of AP1.

ABC MODEL OF FLORAL DEVELOPMENT  (^) ABC model of floral development explains the genetics behind the formation of different whorls in a flower.  (^) The 4 whorls are sepal,petal,stamens & carpel  (^) First formulated by George Haughn and Chris Somerville in 1988  Experimental material was Arabidopsis thaliana

 A class genes : APETALA 1 (AP1) and APETALA2 (AP2) Act to specify petal and sepal development  ▪ B class gene: APETALA 3 (AP3) and PISTILLAH Act to specify Petal and stamen development  ▪ C class gene: AGAMOUS (AG) Act to specify Stamen and carpel development

Mutations in ABC

Genes

 (^) Class A,B &C genes are homeotic genes.They determine the identity of different floral organs and induce the organs to develop in their respective whorls.  (^) The homeotic mutants have defects in floral organ development and induce the right organ develop into wrong whorls/place.Eg:petals develop in the whorl were stamens are normally formed.  (^) Any mutations in class A genes with defects in floral organ development will invite class C genes to express in whorl 1&2.  (^) The class C gene in class A mutants,will express in whorls 1&2 in addition to the normal Whorls 3&4.  (^) Similarly any mutation in class c gene with defects in floral organ development will lead to the encroachment of the

 Mutations in class B genes results in flowers with sepals in the outer two whorls and carpels in the inner two Whorls.  Class B mutant(apetala3), contains loss of functions B genes. Class A genes express in whorls 1&2. As a result sepals are formed in both Whorls 1&2. Class C gene express in whorls 3&4,so carpels are formed in this Whorls.

 Mutations in the Class C gene –AG result in class A activity in all 4 whorls.  The AG mutants produced indeterminate flowers repeating the pattern of organs( se pe pe)n