Extended Data Fig. 1: By TEM, mith1 and saga1 mutant pyrenoids are missing the canonical matrix-traversing membranes observed in wild-type pyrenoids.

a, Graph depicting for each strain the percentage of pyrenoids with membranes seen entering the matrix surface or interior. n = 78 pyrenoids. b, TEM images of wild-type pyrenoids. c-j, TEM images of mith1 and saga1 mutant pyrenoids, organized into categories based on membrane contact with the pyrenoid. The ‘No membranes’ (c, g) category indicates that no membranes are seen in the pyrenoid. The ‘Membrane touches surface’ (d, h) category indicates that membranes are seen touching the surface of the pyrenoid, but are not seen entering the pyrenoid matrix. The ‘Membrane in outer portion of matrix’ category (e, i) describes pyrenoids where membranes are seen in the outer portion of the pyrenoid matrix. The ‘Membrane in matrix interior’ category (f, j) includes pyrenoids where membrane is seen at the interior of the matrix. All images are presented at the same scale as 1(b).