Multi-gene metabolic engineering of tomato plants results in increased fruit yield up to 23%

Abstract

The capacity to assimilate carbon and nitrogen, to transport the resultant sugars and amino acids to sink tissues, and to convert the incoming sugars and amino acids into storage compounds in the sink tissues, are key determinants of crop yield. Given that all of these processes have the potential to co-limit growth, multiple genetic interventions in source and sink tissues, plus transport processes may be necessary to reach the full yield potential of a crop. We used biolistic combinatorial co-transformation (up to 20 transgenes) for increasing C and N flows with the purpose of increasing tomato fruit yield. We observed an increased fruit yield of up to 23%. To better explore the reconfiguration of metabolic networks in these transformants, we generated a dataset encompassing physiological parameters, gene expression and metabolite profiling on plants grown under glasshouse or polytunnel conditions. A Sparse Partial Least Squares regression model was able to explain the combination of genes that contributed to increased fruit yield. This combinatorial study of multiple transgenes targeting primary metabolism thus offers opportunities to probe the genetic basis of metabolic and phenotypic variation, providing insight into the difficulties in choosing the correct combination of targets for engineering increased fruit yield.

Molecular cues of sugar signaling in plants

“…, branching in main inflorescence, and branching in side inflorescences A functional TPP enzyme acts upstream of the RA1 transcription factor to regulate inflorescence branching(Sun et al, 2016) short-day condition Sugar as a positive element for FT expression(Sun et al, 2016(Sun et al, ) al., 1995Vallarino et al, 2020) Transgenic Solanum tuberosum Accumulation sucrose and glucose Flower approximately 2-4 weeks earlierAntisense suppression of AGPase(Muller-Rober et al, 1992;Vallarino et al, 2020) Leaf senescenceArabidopsisGlucoseWithdrawn of nutrients from the old leaves Signal a reduced requirement for investment in Rubisco and other photosynthetic proteins in the old leaves, releasing nitrogen that would become available for the growth of young leaves and for fruit and seed formation(Khan et al, 2020;Wingler et al, 2009Wingler et al, ) al., 2010Zhang et al, 2020) with auxin and cytokinin to initiate the replication and cell division activity. Sugar also regulates CYCD (CYCLIN D) associated with CDKA in the G 1 inter-phase, whereas it activates TOR kinase to phosphorylate the S6K (ribosomal S6 kinase) associated with RETINOBLASTOMA-RELATED 1 eukaryotic TF 2B and CDKA-CYCD complexes in the S-phase for inducing cell elongation(Chevalier et al, 2014;McCready et al, 2020).…”

Leaf specific overexpression of a mitochondrially-targeted glutamine synthetase in tomato increased assimilate export resulting in earlier fruiting and elevated yield

“…Even more so given that the final fruit yield is additionally enhanced. As such this finding was perhaps surprisingly far more successful than our previous attempts to achieve this using multi-gene approaches (Vallarino et al, 2020).…”

“…Leaf gas exchange and chlorophyll fluorescence were performed using a Li- 6400XT (Li-Cor Inc., Lincoln, NE, USA). All measurement conditions were as described by (Vallarino et al, 2020).…”

“…Despite the fact that considerable advances and notable successes have been made in engineering plant metabolism (Zhu et al, 2017; Mangel et al, 2019; Vallarino et al, 2020; Hsieh et al, 2021) our ability to rationally manipulate central metabolism that provides constituents for biomass and other outputs remains limited, largely because of the highly interconnected nature of the central metabolic network. It is therefore essential to approach metabolism from a systematic perspective when developing hypotheses for metabolic engineering (Sweetlove et al, 2017) and computational models are central to this endeavour (Küken and Nikoloski, 2019; Clark et al, 2020).…”

“…A recent study in pea shows that enhanced sucrose partitioning from source to sink results in modifications in leaf C and N metabolism as well as amino acid transport to sinks in order to accommodate the increased assimilate demand of growing seeds (Lu et al, 2020). Indeed, taking such a combined strategy whereby both C and N metabolism are simultaneously altered appears particularly prudent given difficulties in enhancing tomato fruit yield following multi-gene transformation strategies (Vallarino et al, 2020).…”