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Title: CLONING AND CHARACTERIZATION OF A FLORICAULA/LEAFY ORTHOLOG, PFL, IN POLYGAMOUS PAPAYA

Author
item YU, QINGYI - HARC
item Moore, Paul
item Albert, Henrik
item ROADER, A.H.K. - UC, SAN DIEGO
item MING, RAY - HARC

Submitted to: Experimental Cell Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/26/2005
Publication Date: 8/20/2005
Citation: Yu, Q., Moore, P.H., Albert, H.H., Roader, A., Ming, R. 2005. Cloning and characterization of a Floricaula/leafy ortholog, PFL, in polygamous papaya. Experimental Cell Research. 15(8):576-584.

Interpretive Summary: A better understanding of the genetic basis of flowering could lead to more stable and higher levels of productivity of fruit and seed producing crops. The network of flower meristem identity genes that control the transition of plants from vegetative to reproductive states is apparently conserved among plants having flowers with both male and female sex organs (hermaphrodite), but has been inadequately studied in plants such as papaya that have different sex forms (male, female, or hermaphrodite). We used the Arabidopsis LFY flowering gene cDNA clone to isolate an orthologous gene, PFL, from papaya and showed that it is expressed at a relatively low level in vegetative tissues and at a higher level in flower buds of all three sex types. Although PFL appears to important in the development of flowers it does not interfere with leaf production nor is it involved in sex expression; these traits must involve the interaction of PFL with additional regulatory genes yet to be discovered.

Technical Abstract: The homologous genes FLORICAULA (FLO) in Antirrhinum and LEAFY (LFY) in Arabidopsis are known to regulate the initiation of flowering in these two distantly related plant species. These genes are necessary also for the expression of downstream genes that control floral organ identity. We used Arabidopsis LFY cDNA as a probe to clone and sequence a papaya ortholog of LFY, PFL. It encodes a protein that shares 61% identity with the Arabidopsis LFY gene and 71% identity with the LFY homologs of the two woody tree species: California sycamore (Platanus racemosa) and black cottonwood (Populus trichocarpa). Despite the high sequence similarity in two conserved regions, there is a significant difference between the papaya PFL and its counterparts in the proline-rich motif. This difference may not affect the gene function, since an equally divergent but similarly functioning LFY ortholog NEEDLY of Pinus radiata has been reported. Genomic and BAC Southern analyses indicated that there is only one copy of PFL in the papaya genome. In situ hybridization experiments demonstrated that PFL is expressed at a relatively low level in leaf primordia, but it is expressed at a high level in the floral meristem. Quantitative PCR analyses revealed that PFL was expressed in flower buds of all three sex types - male, female, and hermaphrodite with marginal difference between hermaphrodite and unisexual flowers. These data suggest that PFL plays a similar role as LFY in flower development and has limited effect on sex differentiation in papaya.