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 metabolism. Most studies in C 4 plants have focused on photosynthetic PEPC, but less is known about nonphotosynthetic PEPC isozymes, especially with respect to their physiological functions. In this work, we analyzed the precise roles of the sorghum (Sorghum bicolor) PPC3 isozyme by the use of knock-down lines with the SbPPC3 gene silenced (Ppc3 lines). Ppc3 plants showed reduced stomatal conductance and plant size, a delay in flowering time, and reduced seed production. In addition, silenced plants accumulated stress indicators 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 deeper impact on central metabolism in silenced plants compared to wild type, more notably in roots, with Ppc3 plants showing higher nitrate reductase and NADH-glutamate synthase activity in roots and the accumulation of molecules with a higher N/C ratio. Taken together, our results show that although SbPPC3 is predominantly a root protein, its absence causes deep changes in plant physiology and metabolism in roots and leaves, negatively affecting maximal stomatal opening, growth, productivity, and stress responses in sorghum plants. The consequences of SbPPC3 silencing suggest that this protein, and maybe orthologs in other plants, could be an important target to improve plant growth, productivity, and resistance to salt stress and other stresses where non-photosynthetic PEPCs may be implicated.

Silencing of SbPPCK1-3 Negatively Affects Development, Stress Responses and Productivity in Sorghum

“…In Arabidopsis, the knockout of any AtPPC gene delayed flowering [22], and seed yield was found to be highly reduced [32], especially in the ppck1 − plant. In sorghum, delayed flowering and decreased yield were also observed in plants where the SbPPC3 gene had been silenced (Ppc3 line) [21]. These observations indicate that all PEPC and PEPCk isozymes are needed for correct reproductive development and that phosphorylation of PEPC is essential in this respect.…”

“…On the other hand, in the Ppck-2 line, the lack of phosphorylation of root PEPC would be responsible for decreased biomass production (shoots, roots, and seeds) and delayed flowering. SbPPC3 is the main PEPC isozyme responsible for root PEPC activity in sorghum [21]. Accordingly, SbPPC3 silencing caused decreased root and shoot biomass production, a delay in flowering time, and reduced seed production in the Ppc3 plant.…”

“…The increase in the phosphorylation state of PEPC caused augmented malate synthesis, and it could contribute to alleviating carbon deficiency under salinity. In sorghum roots, salinity increased PEPC and PEPCk activity, and SbPPC3 and SbPPCK2 gene expression [21]. Likewise, salinity increased AtPPC3 expression, PEPC activity and its phosphorylation state, and L-malate content in Arabidopsis roots [22].…”

Combined BSA-Seq and RNA-Seq Reveal Genes Associated with the Visual Stay-Green of Maize (Zea mays L.)

“…In transformed plants, photosynthetic efficiency was increased and correlated with higher accumulation of chlorophyll, decreased NPQ, increased PSII, and increased ETR [41]. In sorghum, phosphoenolpyruvate carboxylase 3 knockdown has a detrimental effect on growth, productivity, and responses to salt stress [42]. Interestingly, in previous studies, it has been proposed that this gene is a candidate gene for the stay-green mutant [10]; it is necessary to further explore and validate this proposal.…”

Sorghum: A Multipurpose Crop

“…The domestication of cereal crops has long been focused on increasing grain yield and quality, − and a series of common phenotypes have been sieved around this aspect, such as increased apical dominance, increased tillering, reduced seed shedding, increased quantity and quality, and other traits. − In addition to improving yields and reducing grain losses, nutritional improvement of grain sorghum is now receiving increasing attention. Compared with other food crops, sorghum foods are rich in high-antioxidant anthocyanins, rich polyphenols, and other healthful substances, which makes health food developed from sorghum grains as raw materials popular among consumers. − , Therefore, it is increasingly important to improve sorghum yields to alleviate food problems and develop multifunctional foods from grain sorghum …”