16-DNA sequence-PI - DNA Sequence April 2007 18(2 120130...

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FULL LENGTH RESEARCH PAPER Heterotopic expression of B-class floral homeotic genes PISTILLATA/GLOBOSA supports a modified model for crocus ( Crocus sativus L.) flower formation APOSTOLOS KALIVAS 1 , KONSTANTINOS PASENTSIS 2 , ALEXIOS N. POLIDOROS 2 ,& ATHANASIOS S. TSAFTARIS 1,2 1 Department of Genetics and Plant Breeding, AUTh, Thessaloniki, GR-540 06, Greece, and 2 Institute of Agrobiotechnology, CERTH, Thermi, GR-570 01, Greece (Received 5 June 2006) Abstract For uncovering and understanding the molecular mechanisms controlling flower development in cultivated Crocus sativus and particularly the transformation of sepals in outer whorl (whorl 1) tepals, we have cloned and characterized the expression of a family of five PISTILLATA / GLOBOSA -like ( PI / GLO -like) MADS-box genes expressed in the C. sativus flower. The deduced amino acid sequences of the coded proteins indicated high homology with members of the MADS-box family of transcription factors, and particularly with other members of the PI/GLO family of MADS-box proteins that control floral organ identity. PI/GLO expression studies in cultivated C. sativus uncover the presence of PI/GLO transcripts not only in the second and third whorls of flower organs as expected, but also in the outer whorl tepals that are the sepals in most typical flowers. This heterotopic expression of both B-class genes: PI/GLO and AP3/DEF , known to form heterodimers for stamens and petals (petaloid inner whor l–whorl 2-tepals in C. sativus ), explains the homeotic transformation of sepals into outer whorl tepals in this species. Analysis of PI/GLO sequences from C. sativus for putative targets to known micro-RNAs (miRNAs) showed that the target site for ath-miRNA167 found in Arabidopsis thaliana PI is not present in C. sativus , however, the PI/GLO sequences may be regulated by an ath-miRNA163. Keywords: Crocus sativus, saffron, PISTILLATA/GLOBOSA , tepal formation, micro-RNA target analysis Introduction The discovery of the first MADS-box genes was achieved with the use of genetic and molecular analysis of floral homeotic mutants of Antirrhinum majus and Arabidopsis thaliana (Schwarz-Sommer et al. 1990; Yanofsky et al. 1990). These initial genetic studies led to the proposal of the ABC model of flower development (Coen and Meyerowitz 1991). According to this model, flower organs arranged in four homocentric whorls on the flower originate as follows: sepals in the outmost whorl 1 from the action of A-class MADS-box genes alone; petals in whorl 2 from the combined action of A-class and B-class MADS-box genes; stamens in whorl 3 from the combined action of B-class and C-class MADS- box genes; and finally carpels in the inner whorl 4 from the action of C-class MADS-box genes alone. In A. thaliana ,c l a s sA MADS-box genes are represented by APETALA1 ( AP1 ) and APETALA2 ( AP2 ), class B genes comprise APETALA3 ( AP3 ) and PISTILLATA ( PI ), with DEFICIENS ( DEF ) and GLOBOSA ( GLO )i ti s A. majus counterparts and class C gene is AGAMOUS ( AG )in A. thaliana . The A-, B- and C-function genes encode MADS-domain
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This note was uploaded on 09/13/2010 for the course DGPB 024e taught by Professor Alexiospolidoros during the Spring '10 term at Aristotle University of Thessaloniki.

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16-DNA sequence-PI - DNA Sequence April 2007 18(2 120130...

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