Fig. 1.

Evolution of forisomes in the Fabaceae family and structural analysis of forisomes from D. panamensis. (A) In vivo CLSM image of a D. panamensis forisome stained with sulphorhodamine 101. The tail, clearly visible as a bright streak in the image, pervades the main body of the forisome, which is revealed by lower-intensity fluorescence. (B–H) TEM of D. panamensis forisomes. (B) A condensed forisome in a mature sieve element. (C) Cross-section of a condensed forisome, indicating its typical cuboid shape. The tail is shown in the centre (arrow). (D) Expanded forisome located close to the sieve plate in a mature sieve element. The tail remains condensed (arrow). (E) Cross-section of an expanded forisome. The outline of the protein body is not yet expanded. The condensed tail is visible in the centre (arrow). (F) Expanded forisome with the condensed tail pervading the main body. (G) Magnification of the main body of a condensed forisome, showing fine 10-nm cross-striations (indicated by white lines). (H) Magnification of the tail reveals coarse cross-striations with a periodicity of 40 nm (indicated by white dotted lines), overlaid by a fine 10-nm cross-striation (indicated by white lines). (I) Simplified Fabaceae phylogenetic tree (modified from LPWG, 2013) showing the subfamilies Caesalpinioideae, Mimosoideae and Papilionoideae, the major Papilionoideae clades and the species we investigated. Smaller clades are not shown. Forisomes are only present in the Papilionoideae. The ‘basal papilionoids’ represent the first branching papilionoid lineages (Pennington et al., 2001). Branch lengths do not reflect phylogenetic distances. Sieve plates are marked with an asterisk. Scale bars: (A, B, D, F) = 2 μm, (C, E) = 500 nm, (G, H) = 100 nm.