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 developme nt in Arabidopsis, a construct containing beta -glucuronidase (GUS) gene dr iven by APETALA1 promoter (AP1::GUS) was introduced into emf fwa and emf ft double mutants. GUS activity was strongly detected on shoot meristem of em f1-1 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, e mf2-1 fwa-1, emf2-3 fwa-1 and emf2-3 ft-1 double mutants harboring API::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 fn,a-l seedlings . During this time, only sessile leaves were produced. Further analysis ind icated that API was strongly expressed in 10-day-old emf1-1 and emf2-1 Sing le mutants. Its expression was significantly reduced in all emf1-1 or emf2- 1 late-flowering double mutants tested. Similar to API, the expression of L EA FY(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 API and LFY is dependent not only on the low E MF and FWA activities but also on the expression of most of the late-flower ing genes such as FT, FCA, FE, CO and GI,These data also reveal that most l ate-flowering genes may function downstream of EMF or in pathways distinct from EI)IF to activate genes specified floral meristem identity during shoo t maturation in Arabidopsis.