title: Increased CiFT abundance in the stem correlates with floral induction by low temperature in Satsuma mandarin (Citrus unshiu Marc.).
abstract: After several years in the juvenile phase, adult citrus trees show seasonal periodicity of flowering. A prolonged exposure to low temperature is one of the most important environmental cues for floral induction in citrus. In the present study, the expression of flowering-related genes during the annual cycle of flowering and inductive low-temperature treatment in Satsuma mandarin (Citrus unshiu Marc.) trees is investigated. Simultaneously, floral induction, which occurs before the period of morphological flower development, was estimated as the number of flowers after the forcing of sprouting by defoliation at 25 degrees C. The expression of citrus FLOWERING LOCUS T homologues, CiFT, showed a seasonal increase during the floral induction period and was also induced by an artificial low-temperature treatment (15 degrees C) at which floral induction occurred. By contrast, the mRNA level of CiFT did not show any distinct changes following a warm-temperature treatment (25 degrees C) for 2.5 months, during which time floral induction was completely suppressed. Changes in the expression of the citrus homologues of TERMINAL FLOWER 1, LEAFY, and APETALA1 did not show any correlation with floral induction in the field or under artificial low-temperature conditions. In juvenile seedlings of Satsuma mandarin, which does not flower even under inductive low-temperature conditions, the mRNA levels of CiFT were not affected by the low-temperature treatment, unlike adult tissues. These results suggest that low temperature promotes floral induction via the activation of CiFT transcription in adult Satsuma mandarin trees and that, in the juvenile plant, CiFT transcription does not respond to low temperature.
authors.affiliation: Department of Citrus Research, National Institute of Fruit Tree Science, National Agricultural Research Organization, 424-0292, Okitsu Shimizu-ku, Shizuoka, Japan. fumien@affrc.go.jp
authors.forename: Fumie
authors.initials: F
authors.lastname: Nishikawa
authors.forename: Tomoko
authors.initials: T
authors.lastname: Endo
authors.forename: Takehiko
authors.initials: T
authors.lastname: Shimada
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Fujii
authors.forename: Tokurou
authors.initials: T
authors.lastname: Shimizu
authors.forename: Mitsuo
authors.initials: M
authors.lastname: Omura
authors.forename: Yoshinori
authors.initials: Y
authors.lastname: Ikoma
mesh_terms: D000595:Amino Acid Sequence; D002957:Citrus / Q000235:genetics / Q000378:metabolism*; D003080:Cold Temperature; D035264:Flowers / Q000378:metabolism*; D018506:Gene Expression Regulation, Plant; D008969:Molecular Sequence Data; D010802:Phylogeny; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism*; D018547:Plant Stems / Q000378:metabolism*; D012621:Seasons; D013997:Time Factors
chemical_list: D010940:Plant Proteins