Pho1a (plastid starch phosphorylase) is duplicated and essential for normal starch granule phenotype in tubers of Solanum tuberosum L

Protein targeting to Starch 2 and the plastidial phosphorylase 1 revealed protein-protein interactions with photosynthesis proteins in yeast two-hybrid screenings

Starch metabolism in plants involves a complex network of interacting proteins that work together to ensure the efficient synthesis and degradation of starch. These interactions are crucial for regulating the balance between energy storage and release, adapting to the plant's developmental stage and environmental conditions. Several studies have been performed to investigate protein-protein interactions (PPIs) in starch metabolism complexes, yet it remains impossible to unveil all of the PPIs in this highly regulated process. This study uses yeast-two-hybrid (Y2H) screening against the Arabidopsis leaf cDNA library to explore PPIs, focusing on the starch-granule-initiating protein named Protein Targeting to Starch 2 (PTST2, At1g27070) and the protein involved in starch and maltodextrin metabolism, namely, plastidial phosphorylase 1 (PHS1, EC 2.4.1.1). More than 100 positive interactions were sequenced, and we found chloroplastidial proteins to be putative interacting partners of PTST2 and PHS1. Among them, photosynthetic proteins were discovered. These novel interactions could reveal new roles of PTST2 and PHS1 in the connection between starch metabolism and photosynthesis. This dynamic interplay between starch metabolism and other chloroplast functions highlights the importance of starch as both an energy reservoir and a regulatory component in the broader context of plant physiology and adaptation.

Do storage reserves contribute to plant phenotypic plasticity?

The widespread colonization of diverse habitats by plants is attributed to their ability to adapt to changing environments through environmental phenotypic plasticity. This flexibility, particularly in carbon turnover, allows plants to adjust their physiology and development. Plants store carbon reserves as a metabolic strategy to overcome adversity, with a variety of isozymes evolving to enhance metabolic plasticity. Among these isoforms, some with entirely new functions have emerged, involved in novel metabolic pathways for carbon storage. Here, we discuss the role of these carbon stores, their impact on plant plasticity, methods by which such metabolic plasticity can be analyzed, and evolutionary aspects that have led to well-characterized as well as less well-known molecular mechanisms underlying carbon storage.

Distinct effects of PTST2b and MRC on starch granule morphogenesis in potato tubers

The molecular mechanisms underpinning the formation of the large, ellipsoidal starch granules of potato tuber are poorly understood. Here, we demonstrate the distinct effects of PROTEIN TARGETING TO STARCH2b (PTST2b) and MYOSIN RESEMBLING CHLOROPLAST PROTEIN (MRC) on tuber starch granule morphology. A gene duplication event in the Solanaceae resulted in two PTST2 paralogs (PTST2a and PTST2b). PTST2b is expressed in potato tubers, and unlike PTST2a, it had no detectable interaction with STARCH SYNTHASE 4. MRC expression was detectable in leaves, but not in tubers. Using transgenic potato lines in the variety Clearwater Russet, we demonstrate that MRC overexpression leads to the formation of granules with aberrant shapes, many of which arise from multiple initiation points. Silencing PTST2b led to the production of striking near-spherical granules, each arising from a single, central initiation point. Contrary to all reported PTST2 mutants in other species, we observed no change in the number of granules per cell in these lines, suggesting PTST2b is specifically involved in the control of starch granule shape. Starch content and tuber yield per plant were not affected by PTST2b silencing, but MRC overexpression led to strong decreases in both parameters. Notably, the spherical granules in PTST2b silencing lines had a distinctively altered pasting profile, with higher peak and final viscosity than the wild type. Thus, PTST2b and MRC are promising target genes for altering starch granule size and shape in potato tubers, and can be used to create novel starches with altered physicochemical and/or functional properties.

Understanding starch biosynthesis in potatoes for metabolic engineering to improve starch quality: A detailed review

Potato tubers accumulate substantial quantities of starch, which serves as their primary energy reserve. As the predominant component of potato tubers, starch strongly influences tuber yield, processing quality, and nutritional attributes. Potato starch is distinguished from other food starches by its unique granule morphology and compositional attributes. It possesses large, oval granules with amylose content ranging from 20 to 33 % and high phosphorus levels, which collectively determine the unique physicochemical characteristics. These physicochemical properties direct the utility of potato starch across diverse food and industrial applications. This review synthesizes current knowledge on the molecular factors controlling potato starch biosynthesis and structure-function relationships. Key topics covered are starch granule morphology, the roles and regulation of major biosynthetic enzymes, transcriptional and hormonal control, genetic engineering strategies, and opportunities to tailor starch functionality. Elucidating the contributions of different enzymes in starch biosynthesis has enabled targeted modification of potato starch composition and properties. However, realizing the full potential of this knowledge faces challenges in optimizing starch quality without compromising plant vigor and yield. Overall, integrating multi-omics datasets with advanced genetic and metabolic engineering tools can facilitate the development of elite cultivars with enhanced starch yield and tailored functionalities.

Allelic variation in the autotetraploid potato: genes involved in starch and steroidal glycoalkaloid metabolism as a case study

BACKGROUND

Tuber starch and steroidal glycoalkaloid (SGA)-related traits have been consistently prioritized in potato breeding, while allelic variation pattern of genes that underlie these traits is less explored.

RESULTS

Here, we focused on the genes involved in two important metabolic pathways in the potato: starch metabolism and SGA biosynthesis. We identified 119 genes consisting of 81 involved in starch metabolism and 38 in the biosynthesis of steroidal glycoalkaloids, and discovered 96,166 allelic variants among 2,169 gene haplotypes in six autotetraploid potato genomes. Comparative analyses revealed an uneven distribution of allelic variants among gene haplotypes and that the vast majority of deleterious mutations in these genes are retained in heterozygous state in the autotetraploid potato genomes. Leveraging full-length cDNA sequencing data, we find that approximately 70% of haplotypes of the 119 genes are transcribable. Population genetic analyses identify starch and SGA biosynthetic genes that are potentially conserved or diverged between potato varieties with varying starch or SGA content.

CONCLUSIONS

These results deepen the understanding of haplotypic diversity within functionally important genes in autotetraploid genomes and may facilitate functional characterization of genes or haplotypes contributing to traits related to starch and SGA in potato.