FILAMENTOUS FLOWER, a meristem and organ identity gene of Arabidopsis, encodes a protein with a zinc finger and HMG-related domains

Abstract

Distinctive from that of the animal system, the basic plan of the plant body is the continuous formation of a structural unit, composed of a stem with a meristem at the top and lateral organs continuously forming at the meristem. Therefore, mechanisms controlling the formation, maintenance, and development of a meristem will be a key to understanding the body plan of higher plants. Genetic analyses of filamentous flower (fil) mutants have indicated that FIL is required for the maintenance and growth of inflorescence and floral meristems, and of floral organs of Arabidopsis thaliana. FIL encodes a protein carrying a zinc finger and a HMG box-like domain, which is known to work as a transcription regulator. As expected, the FIL protein was shown to have a nuclear location. In situ hybridization clearly demonstrated that FIL is expressed only at the abaxial side of primordia of leaves and floral organs. Transgenic plants, ectopically expressing FIL, formed filament-like leaves with randomly arranged cells at the leaf margin. Our results indicate that cells at the abaxial side of the lateral organs are responsible for the normal development of the organs as well as for maintaining the activity of meristems.[Key Words: Arabidopsis; FIL; zinc finger; HMG; nuclear protein; abaxial-adaxial development]Received January 29, 1999; revised version accepted March 2, 1999.Differing from the situation in animal systems, maintenance of the meristem activity throughout life is a key for the patterning of the plant body. The shoot apical meristem and the meristem of the main root are formed in embryonic development and kept active after germination. During vegetative growth, leaves are continuously formed in a strictly controlled fashion from the shoot apical meristem. After the plant shifts to reproductive growth, the meristem converts to an inflorescence meristem, which in turn forms floral meristems. The floral meristem generates floral organs at predetermined positions. Genetic and molecular studies are under way to help understand the genetic regulatory system supporting meristem activity: control of cell division, formation of lateral organ primordia, and maintenance of the meristem structure. Recent studies using Arabidopsis, snapdragon, and maize have started to unveil the genetic basis of these molecular mechanisms (Okada and Shimura 1994).The leaf meristems are formed in a helical manner at the top of the inflorescence. When the leaf primordia begin to form, the petiole and flattened leaf blade are developed and the leaves show epinasty. Mature leaves show abaxial-adaxial polarity. The adaxial surface bears glossy, dark green epidermal cells, and produces many trichomes. On the contrary, the abaxial surface shows matte, gray-green epidermal cells and does not produce any trichomes. As the plant grows, the adaxial surface of the newly made leaves undergoes a gradual reduction in production of trichomes, and the abaxial surface starts to produce them. An Antirrhinum phantastica (phan) mutant produces filamentous leaves th...

Organ Polarity in Plants Is Specified through the Opposing Activity of Two Distinct Small Regulatory RNAs

“…In Arabidopsis, establishment of abaxial identity further requires the activities of members of the YABBY and AUXIN RESPONSE FACTOR (ARF) families (Sawa et al 1999;Siegfried et al 1999;Pekker et al 2005). The YABBY genes FILAMENTOUS FLOWER (FIL) and YAB3 act, at least in part, downstream of the HD-ZIPIII and KAN genes, whereas ARF3/ETT and ARF4 affect organ polarity through a distinct pathway (Sawa et al 1999;Siegfried et al 1999;Kumaran et al 2002;Pekker et al 2005).…”

“…The YABBY genes FILAMENTOUS FLOWER (FIL) and YAB3 act, at least in part, downstream of the HD-ZIPIII and KAN genes, whereas ARF3/ETT and ARF4 affect organ polarity through a distinct pathway (Sawa et al 1999;Siegfried et al 1999;Kumaran et al 2002;Pekker et al 2005). ARF3/ETT is expressed more broadly than ARF4, but both transcription factors colocalize in the abaxial domain of leaf primordia, where they act in combination with KAN proteins to promote abaxial fate (Pekker et al 2005).…”

A Conserved microRNA Signal Specifies Leaf Polarity

“…The maize and Arabidopsis yabby genes may share a role in mediating lateral outgrowth along the adaxial/abaxial boundary (Eshed et al 2004;Juarez et al 2004a). However, the Ara- bidopsis YABBY genes also specify abaxial fate, and this function is not conserved in maize (Sawa et al 1999;Siegfried et al 1999;Kumaran et al 2002). Moreover, the miRNA loci involved in adaxial/abaxial patterning have diverged between Arabidopsis, rice, and maize.…”

“…Once this adaxial/abaxial polarity is established, it is interpreted by other downstream genes that lead to the differentiation of adaxial and abaxial specific cell types and to mediolateral blade outgrowth at the adaxial/abaxial boundary (Waites and Hudson 1995). Among these are the YABBY genes, a third family of transcriptional regulators, that act at least in part downstream of the HD-ZIPIII and KAN genes and are required for abaxial cell fate and lamina expansion (Sawa et al 1999;Siegfried et al 1999;Eshed et al 2001Eshed et al , 2004Kumaran et al 2002).…”

Functional complementation analysis in potato via biolistic transformation with BAC large DNA fragments

“…Hamilton et al ͑1996͒ reported stable integration of 150 kb of human DNA in the tobacco genome by Agrobacterium-mediated transformation with a binary BAC vector. A TAC ͑transformation-competent artificial chromosome͒ binary vector was used for Agrobacterium-mediated transformation of Arabidopsis with large DNA fragments ͑Liu et al 1999; Sawa et al 1999;Sato et al 2001͒. Biolistic transformation with whole BAC DNA offers an alternative method for transferring large DNA fragments into plant genomes.…”