Fig. 6.

A proposed model for the function of SAGA1. (A) Multiple proteins link starch and the Rubisco matrix. SAGA1 plays a role at the periphery of starch granules in restricting starch granule elongation. (B) Loss of SAGA1 results in elongated starch granules. (C) The elongated starch granules have increased surface area and their affinity for Rubisco favors a configuration of the Rubisco matrix that has increased surface area, resulting in multiple pyrenoids. (D) There is only 1 “knot” of thylakoid tubules per cell and, as a consequence, the extra pyrenoids in the saga1 mutant lack thylakoid tubules.