Knock-down of phosphoenolpyruvate carboxylase 3 negatively impacts growth, productivity, and responses to salt stress in sorghum (Sorghum bicolor L.)

Abstract

Phosphoenolpyruvate carboxylase (PEPC) is a carboxylating enzyme with important roles in plant metabo-lism. Most studies in C4plants have focused on photosynthetic PEPC, but less is known about non-photosynthetic PEPC isozymes, especially with respect to their physiological functions. In this work, weanalyzed the precise roles of the sorghum (Sorghum bicolor) PPC3 isozyme by the use of knock-down lineswith the SbPPC3gene silenced (Ppc3lines).Ppc3plants showed reduced stomatal conductance and plantsize, a delay in flowering time, and reduced seed production. In addition, silenced plants accumulated stressindicators such as Asn, citrate, malate, and sucrose in roots and showed higher citrate synthase activity,even in control conditions. Salinity further affected stomatal conductance and yield and had a deeperimpact on central metabolism in silenced plants compared to wild type, more notably in roots, withPpc3plants showing higher nitrate reductase and NADH-glutamate synthase activity in roots and the accumula-tion of molecules with a higher N/C ratio. Taken together, our results show that although SbPPC3 is pre-dominantly a root protein, its absence causes deep changes in plant physiology and metabolism in rootsand leaves, negatively affecting maximal stomatal opening, growth, productivity, and stress responses insorghum plants. The consequences of SbPPC3silencing suggest that this protein, and maybe orthologs inother plants, could be an important target to improve plant growth, productivity, and resistance to saltstress and other stresses where non-photosynthetic PEPCs may be implicated.