Unique and redundant functional domains of APETALA1 and CAULIFLOWER, two recently duplicated Arabidopsis thaliana floral MADS-box genes.

APETALA1 (AP1) and CAULIFLOWER (CAL) are closely related MADS box genes that are partially redundant during Arabidopsis thaliana floral meristem determination. AP1 is able to fully substitute for CAL functions, but not vice versa, and AP1 has unique sepal and petal identity specification functions. In this study, the unique and redundant functions of these two genes has been mapped to the four protein domains that characterize type-II MADS-domain proteins by expressing all 15 chimeric combinations of AP1 and CAL cDNA regions under control of the AP1 promoter in ap1-1 loss-of-function plants. The "in vivo" function of these chimeric genes was analysed in Arabidopsis plants by expressing the chimeras. Rescue of flower meristem and sepal/petal identities was scored in single and multiple insert homozygous transgenic lines. Using these chimeric lines, it was found that distinct residues of the AP1 K domain not shared by the same CAL domain are necessary and sufficient for complete recovery of floral meristem identity, in the context of the CAL protein sequence, while both AP1 COOH and K domains are indispensable for complete rescue of sepal identity. By contrast, either one of these two AP1 domains is necessary and sufficient for complete petal identity recovery. It was also found that there were positive and negative synergies among protein domains and their combinations, and that multiple-insert lines showed relatively better rescue than equivalent single-insert lines. Finally, several lines had flowers with extra sepals and petals suggesting that chimeric proteins yield abnormal transcriptional complexes that may alter the expression or regulation of genes that control floral organ number under normal conditions.

Alvarez-Buylla ER ，García-Ponce B ，Garay-Arroyo A 《JOURNAL OF EXPERIMENTAL BOTANY》

Functional analysis of three lily (Lilium longiflorum) APETALA1-like MADS box genes in regulating floral transition and formation.

Chen MK ，Lin IC ，Yang CH 《-》

Direct regulation of the floral homeotic APETALA1 gene by APETALA3 and PISTILLATA in Arabidopsis.

Sundström JF ，Nakayama N ，Glimelius K ，Irish VF ... -  《PLANT JOURNAL》

Four orchid (Oncidium Gower Ramsey) AP1/AGL9-like MADS box genes show novel expression patterns and cause different effects on floral transition and formation in Arabidopsis thaliana.

Four AP1/AGL9 functional MADS box genes were characterized from the orchid (Oncidium Gower Ramsey). OMADS6 is a SEP3 ortholog, OMADS11 is a SEP1/2 ortholog, OMADS7 is an AGL6-like gene and OMADS10 is a putative paleoAP1 ortholog. The identity of these four genes was further supported by the presence of conserved motifs in the C-terminal regions of the proteins. OMADS6 showed an expression pattern different from SEP3 orthologs, with expression in the sepal, petal, lip and carpel, and was barely detected in the stamen. The expression pattern for OMADS11 was similar to OMADS6 and different from SEP1/2 orthologs since its expression was undetectable in the stamen. The expression pattern for OMADS7 was nearly identical to OMADS6. The similarities in the expression patterns of the SEP/AGL6-like genes OMADS6, 11 and 7 indicated that their transcriptional regulation is highly evolutionarily conserved in the orchid. Unlike OMADS6/11/7, OMADS10 was only expressed in vegetative leaves and in the lip and carpel of mature flowers, which distinguishes it from most genes in the SQUA subfamily. Ectopic expression of OMADS6, 11 or 7 caused extremely early flowering, whereas 35S::OMADS10 only caused moderately early flowering in transgenic Arabidopsis plants. In addition, flower organ conversions, such as carpelloid sepals and staminoid petals, were observed in 35S::OMADS6 and carpelloid sepals were produced in 35S::OMADS7, while flower organ conversions were not observed in 35S::OMADS11 or 35S::OMADS10 transgenic flowers. This result reveals possible functional diversification of the orchid AP1/AGL9 genes OMADS6, 11, 7 and 10 in regulating flower transition and formation.

Chang YY ，Chiu YF ，Wu JW ，Yang CH ... -  《-》

The Arabidopsis floral meristem identity genes AP1, AGL24 and SVP directly repress class B and C floral homeotic genes.

Gregis V ，Sessa A ，Dorca-Fornell C ，Kater MM ... -  《-》