EMF genes interact with late-flowering genes in regulating floral initiation genes during shoot development in Arabidopsis thaliana.

To investigate the mechanisms regulating the initiation of floral development in Arabidopsis, a construct containing beta-glucuronidase (GUS) gene driven by APETALA1 promoter (AP1::GUS) was introduced into emf fwa and emf ft double mutants. GUS activity was strongly detected on shoot meristem of emf1-1 single mutants harboring AP1::GUS construct just 5 d after germination. By contrast, GUS activity was undetectable on emf1-1 fwa-1, emf1-1 ft-1, emf2-1 fwa-1, emf2-3 fwa-1 and emf2-3 ft-1 double mutants harboring AP1::GUS construct 10 d after germination. GUS activity was only weakly detected on the apical meristem of 20-day-old emf1-1 fwa-1 and emf2-1 fwa-1 seedlings. During this time, only sessile leaves were produced. Further analysis indicated that AP1 was strongly expressed in 10-day-old emf1-1 and emf2-1 single mutants. Its expression was significantly reduced in all emf1-1 or emf2-1 late-flowering double mutants tested. Similar to AP1, the expression of LEAFY (LFY) was also high in emf1-1 and emf2-1 single mutants and reduced in emf1-1 or emf2-1 late-flowering double mutants. Our results indicate that the precocious expression of AP1 and LFY is dependent not only on the low EMF and FWA activities but also on the expression of most of the late-flowering genes such as FT, FCA, FE, CO and GI. These data also reveal that most late-flowering genes may function downstream of EMF or in pathways distinct from EMF to activate genes specified floral meristem identity during shoot maturation in Arabidopsis.

EMF genes interact with late-flowering genes to regulate Arabidopsis shoot development.

To investigate the genetic mechanisms regulating the transition from vegetative to reproductive phase in Arabidopsis, double mutants between two embryonic flower (emf) and 12 different late-flowering mutants were constructed and analyzed. Double mutants in all combinations displayed the emf phenotypes without forming rosettes during early development; however, clear variations between different double mutants were observed during late development. fwa significantly enhanced the vegetative property of both emf mutants by producing a high number of sessile leaves without any further reproductive growth in emf1 fwa double mutants. It also produced numerous leaf-like flower structures similar to those in leafy ap1 double mutant in emf2 fwa double mutants. Nine late-flowering mutants, ft, fca, ld, fd, fpa, fe, fy, fha, and fve, caused different degrees of increase in the number of sessile leaves, the size of inflorescence, and the number of flowers only in weak emf1 and emf2 mutant alleles background. Two late-flowering mutants, co and gi, however, had no effect on either emf1 and emf2 mutant alleles in double mutants. Our results suggest that FWA function in distinct pathways from both EMF genes to regulate flower competence by activating genes which specify floral meristem identity. CO and GI negatively regulate both EMF genes, whereas the other nine late-flowering genes may interact with EMF genes directly or indirectly to regulate shoot maturation in Arabidopsis.