Fig. 2.
Graft-transmissible florigen enhances the SCWB network in sft and WT recipients. (A) Graft combinations: donor scions (upper part) and recipient shoots (lower part). Stems of lateral recipient shoots (arrowheads) were harvested at 25 d postgrafting. WT, light orange; sp, orange; sft, blue; 35S:SFT, red. (B) A live 35S:SFT//sft graft. Here 5-wk-old plants were grafted with shoots of 35S:SFT donors of the same age. (C) Hierarchical clustering of 593 genes regulated by m-florigen (Padj ≤ 0.1; |FC ≥2|). Almost all SCW genes are clustered in red. (D) Heat map of selected m-florigen-responsive SCW and non- CW genes (from C) and their absolute expression levels in 5 recipient genotypes. Genes are color-coded in accordance with the hierarchical clustering in C and with respect to the categories CW and non-CW. (E) PG1. All expressed genes in the recipients of the leftmost 3 grafts in A were sorted into 9 cohorts based on comparisons of WT//WT vs. sft//sft and SFT//sft vs. sft//sft and subsequently by 3 possible response categories—up (U), down (D) and no change (N)—demanding |FC >1.5| as the cutoff (Materials and Methods). Remarkably, cohort DU, with genes down-regulated in sft of the sft//sft homograft but up-regulated by at least 1.5-fold in comparison with sft of the 35S SFT//sft heterograft, is enriched for the florigen-regulated genes analyzed in C (101 of 593; P < 5.4*10–70 hypergeometric) and for SCWB genes (54 of 365; P < 4.4*10–26). The color-coding of the circles in the line graphs corresponds to the recipient genotypes as in A. Red numbers indicate SCWB genes. (F–I) Distribution and stability of the m-florigen protein in tomato. (F) A dilution series for the SFT-3XMYC protein from donor 35S:SFT-3XMYC leaves (Materials and Methods). (G) M-florigen is accumulated in young and old recipient leaves and stems at approximately 1% of donor leaf levels. L1, old leaves; St M, mature stems; St Y, young stems. (H) MYC tagged m-florigen is distributed among all leaflets of mature recipient leaves. P, a pair of leaflets; Ter, most mature terminal leaflet (on the right). (I) The MYC-tagged, graft-transmissible florigen had a half-life of ∼4 d. (Top) At 20 d postgrafting, the donor 35S:SFT scions were removed, and the presence of mobile SFT-MYC in recipient leaves was recorded daily. (Bottom) Control mobile SFT-MYC from recipient shoots of intact grafts.