Transgenic Expression of Rubisco Accumulation Factor2 and Rubisco Subunits Increases Photosynthesis and Growth in Maize.

Carbon assimilation by Rubisco is often a limitation to photosynthesis and therefore plant productivity. We have previously shown that transgenic co-expression of the Rubisco large (LS) and small (SS) subunits along with an essential Rubisco assembly factor, Raf1, leads to faster growth, increased photosynthesis, and enhanced chilling tolerance in maize (Zea mays). Maize also requires Rubisco Accumulation Factor2 (Raf2) for full accumulation of Rubisco. Here we have analyzed transgenic maize lines with increased expression of Raf2 or Raf2 plus LS and SS. We show that increasing Raf2 expression alone had minor effects on photosynthesis, whereas expressing RAF2 with Rubisco subunits led to increased Rubisco content, more rapid carbon assimilation, and greater plant height, most notably in plants at least six weeks of age. The magnitude of the effects was similar to what was observed previously for expression of Raf1 together with Rubisco subunits. Taken together, this suggests that increasing the amount of either assembly factor with Rubisco subunits can independently enhance Rubisco abundance and some aspects of plant performance. These results could also imply either synergy, or a degree of functional redundancy for Raf1 and Raf2, the latter of whose precise role in Rubisco assembly is currently unknown.