Graft-transmissible action of Arabidopsis FLOWERING LOCUS T protein to promote flowering

Abstract

the shoot apex and activates transcription of meristem identity genes such as APETALA1 (AP1). 10,11 Recent studies from several laboratories have provided strong evidence for the FT protein in Arabidopsis and corresponding proteins in other species being an important part of the florigen. [12][13][14][15][16] These were mainly based on (1) detection in the shoot apex or its vicinity of GFP-fusion or Myc-tagged proteins expressed by promoters with preferential activity in the phloem tissues in Arabidopsis and rice, 12-14 (2) detection of FT-like proteins in the phloem sap from cucurbits, 16 and (3) transmission of FT:GFP protein through a graft junction from donor transgenic plants expressing the fusion protein in the vasculature to recipient ft plants with concomitant promotion of flowering. 12 Because key observations in Arabidopsis 12,14 were based on the effect of cumulative expression by SUCROSE TRANSPORTER 2 (SUC2) promoter which has strong activity in the vasculature within a short distance from the shoot, 12,14,17 it is difficult to analyze the temporal aspects of the transport and to exclude the possibility of short-distance, cellto-cell transport without entering into the phloem. In addition, the ability of GFP for long-distance transport via the phloem and a graft junction 18,19 makes an independent confirmation based on methods other than GFP-fusion protein desirable.Our recent work aimed to resolve these difficulties by the combined use of FT-T7 protein, a local transient induction system, and a two-shoot "Y-grafting" technique originally described by Turnbull and colleagues. 20 Since graft-transmission has been an important criterion of florigen, we first demonstrated the grafttransmissible action of FT both from the endogenous gene and transgenes under the control of 35S promoter and SULPHATE TRANSPORTER 2;1 (SULTR2;1) promoter with preferential expression in the phloem. 19,21 Grafting of a wild-type scion resulted in small but significant reduction in both days to flowering and the number of leaves at flowering of recipient ft-1 stock plants, while grafting of a strong 35S::FT scion caused much greater (more than 20 leaves) reduction (Fig. 1A). Even in the latter case, rescue may sound rather modest, since the recipient ft-1 stock plants still had 20 more leaves than the intact wild-type plants grown in the same conditions. 21 However, given that functional connection of phloem capable of trafficking tracer dyes and enhanced GFP (EGFP) were established about 2 weeks after grafting, by which time wild-type plants made [Plant Signaling & Behavior 4:2, 123-125; February 2009] Seasonal flowering is an important adaptive trait in plants for reproductive success. Plants monitor day length in the leaf to anticipate upcoming seasonal changes and initiate floral morphogenesis at the shoot apex by the action of the leaf-generated mobile florigen. 1-3 FT, a 20-kDa protein, is a conserved potent promoter of flowering. [4][5][6][7] In Arabidopsis, transcription of FT is induced by long days in the phloem tissu...

GmFT2a, a Soybean Homolog of FLOWERING LOCUS T, Is Involved in Flowering Transition and Maintenance

“…That is, FT RNA is only expressed in vascular tissues [46], [47] and FT protein functions in meristems [41], [48]. With evidence from grafting studies, FT protein can be transported from the leaves to the shoot apex to induce flowering [15]–[18]. It is believed that the FT protein could be florigen or a component of florigen [11], [18]–[20].…”

Spatially selective hormonal control of RAP2.6L and ANAC071 transcription factors involved in tissue reunion in Arabidopsis

“…During reconstruction of damaged tissues, vascular and/or other cells are transformed so as to physiologically connect the existing tissues (4,5). Such activities have long been observed in grafting techniques, which are advantageous for agriculture and horticulture (6) and also for basic research on systemic physiological events, such as flower induction (7) and hormone actions (8,9). Low grafting efficiency and tissue incompatibility are often encountered, necessitating an understanding of the healing mechanism underlying grafting.…”

Induction of flowering in cassava through grafting

“…The exogenous application of plant growth regulators successfully induce flowering not only in angiosperm species (Aliyu et al, 2011;Liverman and Lang, 1956;Henny and Chen, 2011) but also in gymnosperms (Luukkanen and Johansson, 1980). Grafting techniques have also been used to take advantage of the mobility of the signal for flowering (Notaguchi et al, 2009). Many decades before the discovery of the FT locus, grafting was exploited to hasten flowering in sweet potato (Kobayashi and Nakanishi, 1982;Zobel and Hanna, 1953), sugar beet (Curtis and Hornsey, 1964), or the Crassulaceae family (Zeevaart, 1978).…”