Fig. 4.

Temperature-dependent tissue regeneration is widespread. (A) Proportion of grafts attached 1-2 DAG after recovery at 20°C or 27°C [±standard error of a proportion (s.e.p.); n=30 plants per temperature per time point]. (B) Callus formation from cut Col-0 petioles at 20°C or 27°C. (C) Callus size 8 days after wounding from various genotypes relative to Col-0 at 20°C (mean±s.d., n=60 cotyledons per genotype and temperature). (D) P. japonicum haustoria numbers with control or NPA applications at 20°C or 27°C (mean±s.d. from four experiments, each with 20 infections per treatment). (E) Proportion of P. japonicum xylem bridge formation with control or NPA applications at 20°C or 27°C (±s.e.p.; n=40 infections per treatment). (F) Representative images of haustoria and xylem bridges formed at 7 DPI at 27°C with and without NPA petiole applications. Dashed lines show the interface between P. japonicum and Arabidopsis. Xylem bridges are indicated by the arrowheads. (G) Relative expression levels of auxin-related genes in P. japonicum at 7 DPI in shoots and roots at 20°C or 27°C (mean±s.d. from three experiments). *P<0.05, **P<0.01, ***P<0.001; Fisher's exact test (A,E) or unpaired two-tailed Student's t-test (C,H) compared with 20°C. (H) Proposed model for temperature-dependent vascular regeneration. Elevated temperatures increase PIF4 levels and activate YUC8-mediated auxin production. Auxin moves to the graft junction where it degrades BDL and activates auxin response factors (ARFs) to promote phloem reconnection. SAM, shoot apical meristem. Scale bars: 250 μm (B); 100 μm (F).