MOLECULAR ASPECTS OF CONTROL OF REPRODUCTIVE GROWTH AND

DEVELOPMENT

Presented By,Chavan Mahadeo Rajaram

ADPM/15/2422Genetics & Plant Breeding

COLLEGE OF AGRICULTURE , DAPOLIM.SC (AGRI)

• Hormones are chemical signals that integrate internal developmental and external environmental inputs and transform them into appropriate responses.

• The responses require specific receptors and a signal-transduction pathway to coordinate downstream responses

Reception Transduction Respones .

Role of auxin• Auxin is an essential hormone that has been

implicated in many aspects of plant growth and development (Woodward and Bartel 2005).

• Auxin plays role in the initiation of flowering and development of reproductive organs.

• A number of plant mutants have been described that affect flowering . In maize, one example is bif2 barren inflorescence.

• A link between auxin and flower development was first established when the auxin transport mutant pin1 was isolated and characterized (Okada et al. 1991; Galweiler et al. 1998).

• Transcription factors responsible for floral meristem

and floral organ develpoment.

• Therefore, flower development provides a great system to analyze the mechanisms by which auxin regulates plant organogenesis and pattern formation.

SIGNAL TRANSDUCTION

Gibberrelin in flower initiation• The ability of gibberellins (GAs) to promote pollen formation

and induction of flowering.

• Gibberellins (GAs) function not only to promote the growth of plant organs, but also to induce phase transitions during development.

• GAs mediate the photoperiodic stimulus to flowering in LD plant.

• In Arabidopsis thaliana, a facultative LD and cold-responsive species, GA contributes to one of four interacting pathways for floral induction

• For photoperiod-enhanced GA biosynthesis in leaves , through up-regulation of GA 20-oxidase gene expression, a signals from leaves to apices in response to LD has been transmitted for flowering.

• In Arabidopsis thaliana, as one of four quantitative floral pathways, in SD, in the absence of the photoperiod flowering pathway, the GA pathway assumes a major role and becomes obligatory.

• Gibberellins promote flowering in Arabidopsis through the activation of genes encoding the floral integrators SUPPRESSOR OF OVEREXPRESSION OF CONSTANS 1 (SOC1), LEAFY (LFY), and FLOWERING LOCUS T (FT) in the inflorescence and floral meristems, and in leaves, respectively.

• These genes encode proteins that activate the floral meristem identity (FMI) geneS APETALA1 (AP1), APETALA2 (AP2),FRUITFULL (FUL), CAULIFLOWER (CAL) and LFY, which convert the vegetative meristem to a floral fate.

• GA signalling is not required for floral organ specification, it is essential for the normal growth and development of these organs.

GA IN vernalisation The cooling of seed

during germination in order to accelerate flowering when it is planted.

Cold treatment activates VER203 gene expression.

GA also induces VER203 expression thus GA can partially substitute cold treatment to initiate flowering in plants that require cold treatment.

ROLE OF CYTOKININ Cytokinin regulates the activity of reproductive

meristems, flower organ size, ovule formation, and thus seed yield.

The cytokinin status of the meristem depends on different factors, including metabolic degradation of the hormone, which is catalyzed by cytokinin oxidase/dehydrogenase (CKX) enzymes.

CKX3 and CKX5 regulate the activity of the reproductive meristems of Arabidopsis thaliana.

CKX3 is expressed in the central WUSCHEL (WUS) domain, while CKX5 shows a broader meristematic expression. ckx3 ckx5 double mutants form larger inflorescence and floral meristems.

Mutation of a negative regulator gene of cytokinin signaling, ARABIDOPSIS HISTIDINE PHOSPHOTRANSFER PROTEIN 6, which is expressed at the meristem flanks, caused a further action.

ROLE OF ETHYLENEThe gaseous hormone which helps for fruit

ripening, floral development and sex expression.

Ethylene (ET) is a notable signaling molecule in higher plants.

In the year 1993 the ET receptor gene, ETR1, was identified; this ETR1 receptor protein being the first plant hormone receptor to be isolated.

FLORIGEN• Florigen (or flowering hormone) is the hypothesized

hormone-like molecule responsible for controlling triggering flowering in plants.

•  Florigen is produced in the leaves, and acts in the shoot apical meristem of buds and growing tips.

• Research into florigen is predominately centred on the model organism and long day plant, Arabidopsis thaliana.

• Mode of action : 1. Photoperiod-regulated initiation 2.Signal translocation via the phloem 3. Induction of flowering at the shoot apical meristem.

• The signal initiation - messenger RNA (mRNA) coding a transcription factor called CONSTANS (CO).

mRNA is then translated into CO protein.

• CO protein promotes transcription of another gene called Flowering Locus T (FT)

• FT protein interacts with a transcription factor (FD protein) to activate floral identity genes.

• Increased expression of at least one direct target gene, APETALA 1 (AP1), along with other targets, such as SOC1 and several SPL genes, which are targeted by a microRNA

Case study….• Integrating hormones into the floral-

transition pathway of Arabidopsis thaliana SETH J. DAVIs

CONCLUSION Physiological and genetic approaches have revealed that different organ parts of Arabidopsis are important for the transition to flowering. Thus, these different tissues/organs must be able to communicate in

order to coordinately regulate floral transition of the plant. Hormonal signals must partially mediate this process.

Recent studies in Arabidopsis have successfully started to dissect the leaf-to-shoot apex relation and identified florigen and two other compounds that are transported from leaves to the apex before the floral transition (Zeevaart 2006, 2008).

It can be argued that one hormonal compound is the phytohormone GA, which could be a component of the florigenic activity under noninductive photoperiodic conditions, thus acting redundantly to the protein factor FT.

Furthermore, the role of diverse phytohormones needs to be coherently integrated, in a full context of signal convergence.

Reference• Bartrina , Otto E, Strnad M, Werner T, Schmülling T.(2011) Cytokinin regulates the

activity of reproductive meristems, flower organ size, ovule formation, and thus seed yield in Arabidopsis thaliana.

• Francisco De la Torre, María del Carmen Rodríguez-Gacio and Angel J Matilla(2006). How Ethylene Works in the Reproductive Organs of Higher Plants.

• Jean-Michel Davière and Patrick Achard.(2013). Gibberellin signaling in plants. Development at a glance

• Youfa Cheng and Yunde Zhao. (2007). A Role for Auxin in Flower Development. Journal of Integrative Plant Biology , 49 (1): 99−104.

• WOUT BOERJAN, BART DEN BOER and MARC VAN MONTAGU. (1992). Molecular genetic approaches to plant development. International journal of biology.36 : 59-66.

• Peter hedden (2008). Gibberellin as a factor in floral biology network. Oxford journal of botany

• Book.goggle.co.in• Wikipedia.• You tube• www.ncbi.co.insss

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