Silencing of Sb Negatively Affects Development, Stress Responses and Productivity in Sorghum.

Phosphoenolpyruvate carboxylase (PEPC) plays central roles in photosynthesis, respiration, amino acid synthesis, and seed development. PEPC is regulated by different post-translational modifications. Between them, the phosphorylation by PEPC-kinase (PEPCk) is widely documented. In this work, we simultaneously silenced the three sorghum genes encoding PEPCk (Sb-) by RNAi interference, obtaining 12 independent transgenic lines ( lines), showing different degrees of Sb silencing. Among them, two T2 homozygous lines ( and ) were selected for further evaluation. Expression of Sb was reduced by 65% and 83% in and illuminated leaves, respectively. Expression of Sb was higher in roots and decreased by 50% in and in this tissue. Expression of Sb was low and highly variable. Despite the incomplete gene silencing, it decreased the degree of phosphorylation of PEPC in illuminated leaves, P-deficient plants, and NaCl-treated plants. Both leaves and seeds of lines had altered metabolic profiles and a general decrease in amino acid content. In addition, lines showed delayed flowering, and 20% of plants did not produce flowers at all. The total amount of seeds was lowered by 50% and 36% in and lines, respectively. The quality of seeds was lower in lines: lower amino acid content, including Lys, and higher phytate content. These data confirm the relevance of the phosphorylation of PEPC in sorghum development, stress responses, yield, and quality of seeds.