Floral induction and development genetic and molecular analysis

intro-flowering time genes influence the duration of vegetative growth-

1. Floral Induction and Development-Genetic and Molecular analysis

2. CONTENTS:- Introduction Flowering time genes influence the duration of Vegetative growth Floral-Identity Genes And Identity Genes Overlap In Time And Function

3. Introduction:- Flower development provides a model system to study mechanisms that govern pattern formation in plants. Most flowers consist of four organ types that are present in specific order from the periphery on the center of the flower. Hear are studies on flower development in one model species. Arabidopsis thaliana Flower development is initiated when that signal arrives at the shoot apical meristem. During the vegitative state the shoot apical meristem is programmed to produce leafe primordial. When the floral signals arrives from the leaf the Meristem acquires floral identity and secondary inflorescence meristems, or floral primordia, arise in the axils of the uppermost leaf primordia .

4. Flowering-Time Genes Influence The Duration Of Vegetative Growth Flowering time genes provide the connection between florigen, or the floral induction signal , and the transition to the floral organs. flowering time mutants many therefore interfere with the production of the signal in the leaf, translocation of the signal to the apex, or its activity in the apex. Most flowering time mutants identified thus far causes plants to flower later than normal, indicating that the mutant interfere with pathways that normally promote flowering. Note that flowering time, as it is used here, refers to a developmental time rather than chronological time. For ex . Arabidopsis is a facultative long day plant with a critical photoperiod of 8 to 10 hour.

5. It is interesting to note that ,although a large number of late-flowering mutants have been described, no single Arabidopsis mutants that remains vegetative indefinitely has yet been identified. This fits with the general assumption that there are multiple pathways controlling flowering time with a certain amount of built in redundancy. Redundancy provides that inactivation of genes in one pathway is at least partially compensated for by other genes or complmentary pathways. In Arabidopsis , at least five separate, but interacting, pathways for controlling flowering time have been identified.

6. Several flowering time mutants, including fac , ld , and fve , flower later than wildtype plants under both LD and SD conditions but remain sensitive to vernalization . Because fiowering in the mutans is equally affected under both LD and SD conditions, the corresponding wildtype genes are thought to be active in an autonomous pathway that monitors developmental stage and initiates flowering in response to internal developmental signals. Such a signal is commonly reflected in a minimum leaf number that must be achieved before flowering can proceed.

7. Flowering of a second group of mutans, including constans (CO) and gigantea (GI),is delayed under LD conditions, but not under SD response. The CO gene is believed to be a central component in the photoperiodic or long day pathway and is responsible for promoting the mobile floral stimulus FT. Both CO and GI have been cloned and studied in some detail. It appears that GI operates before CO in the same pathway and that floral promotion under long days depends on the amount of CO protein and, subsequently, FT protein that is produced. The action of FT at the shoot apical meristem is at least in part mediated by a transcription factor FD.

8. Floral-Identity Genes And Identity Genes Overlap In Time And Function While the principal effect of flowering time mutants is on the duration of vegetative development, mutations in the floral-identity genes disrupt the transition of the floral identity genes disrupt the transition of the undifferentiated primordia to floral meristem.At least four identity genes have been isolated from Arabidopsis: 1. LEAFY(LFY) 2.APETALA1(AP1) 3.APETALA2(AP2) 4.CAULIFLOWER(CAL )

9. The LEAFY gene appears to play a key role in floral meristem identity .This can be demonstrated by placing the gene under control of a strong promoter from the cauliflower mosaic virus. LEAFY appears to have a central role in flowering Process. It is probably the principal target of the mobile stimulus FT when it arrives in the meristem . LEAFY, in turn activates organ identity genes such as APETALA1 . The Arabidopsis flower is rather typical among advanced flowering plants, consisting of four distinct whorls of floral organs. The outermost whorl consists of four sepals, Which are green and leaf like. The next whorl consists of four yellow petals.

10. The third whorl consists six stamen, or male reproductive organs, and the inner most whorl contains two fused carpels at the base of the female reproductive structure, the pistil.

11. Mutations in combination with studies of temporal and spatial expression patterns have identified five genes that are involved in the determination of organ identity : APETALA1(AP1), APETALA2(AP2), APETALA3(AP3), PISTILATA(P1 ) , and AGAMOUS(AG). Note that AP1Vand AP2 have both been previously identified as floral identity genes as well. Mutations in the organ-identity genes generally result in the modification, displacement, or total absence of floral organs. In addition , mutations in any one of these genes generally influence the development of two adjacent floral organs.

12. The influence of organ-identity genes on the development of the Arabidopsis flower can best be understood by viewing the floral meristrem as three overlapping developmental fields or fields gene activity ;Designated A,B and C field A includes the sepals and petals, field B includes the petals and stamens, and field C includes stamens and central carpels . This view is referred to as the ABC model for floral organ specification.

13. REFERENCE :- Introduction to Plant Physiology. William G. Hopkins Norman P. A. Huner WWW.wiley.com/college/hopkins

14. Thank You