Loss of starch synthase IIIa changes starch molecular structure and granule morphology in grains of hexaploid bread wheat

Fahy, Brendan; Gonzalez, Oscar; Ahn‐Jarvis, Jennifer; Warren, Frederick J.; Dunn, Jack; Lovegrove, Alison; Hazard, Brittany

doi:10.1038/s41598-022-14995-0

Cited by 15 publications

(5 citation statements)

References 52 publications

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“…There are numerous examples of altered granule morphology in wheat arising as a consequence of mutations in genes that affect starch polymer biosynthesis and structure (e.g. SS3 and SBE2) or granule initiation patterns (SS4, BGC1 and MRC) (Carciofi et al ., 2012; Chia et al ., 2020; Hawkins et al ., 2021; Chen et al ., 2022a; Fahy et al ., 2022). However, we achieved highly modified granule morphology after mutating a component of plastid division.…”

Section: Discussionmentioning

confidence: 99%

Increasing amyloplast size in wheat endosperm through mutation of PARC6 affects starch granule morphology

et al. 2023

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Summary The determination of starch granule morphology in plants is poorly understood. The amyloplasts of wheat endosperm contain large discoid A‐type granules and small spherical B‐type granules. To study the influence of amyloplast structure on these distinct morphological types, we isolated a mutant in durum wheat (Triticum turgidum) defective in the plastid division protein PARC6, which had giant plastids in both leaves and endosperm. Endosperm amyloplasts of the mutant contained more A‐ and B‐type granules than those of the wild‐type. The mutant had increased A‐ and B‐type granule size in mature grains, and its A‐type granules had a highly aberrant, lobed surface. This morphological defect was already evident at early stages of grain development and occurred without alterations in polymer structure and composition. Plant growth and grain size, number and starch content were not affected in the mutants despite the large plastid size. Interestingly, mutation of the PARC6 paralog, ARC6, did not increase plastid or starch granule size. We suggest TtPARC6 can complement disrupted TtARC6 function by interacting with PDV2, the outer plastid envelope protein that typically interacts with ARC6 to promote plastid division. We therefore reveal an important role of amyloplast structure in starch granule morphogenesis in wheat.

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Section: Discussionmentioning

confidence: 99%

Increasing amyloplast size in wheat endosperm through mutation of PARC6 affects starch granule morphology

et al. 2023

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“…SS2a is also a candidate enzyme that requires more thorough investigation, as it was pulled down with BGC1 ( Table 1 ). Although SS3 can in some circumstances initiate granules in Arabidopsis leaves ( Szydlowski et al 2009 ; Seung et al 2016 ), it is unlikely to play a major role in B-type granule initiation, since SS3a mutants of wheat produce apparently normal B-type granules ( Fahy et al 2022 ). MOS can also be shortened/elongated by the disproportionating enzyme DPE1 ( Critchley et al 2001 ; Lütken et al 2010 ; Hwang et al 2016a ) and shortened by amylolytic activities.…”

Section: Discussionmentioning

confidence: 99%

Initiation of B-type starch granules in wheat endosperm requires the plastidial α-glucan phosphorylase PHS1

Kamble,

Makhamadjonov,

Fahy

et al. 2023

The Plant Cell

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The plastidial α-glucan phosphorylase (PHS1) can elongate and degrade maltooligosaccharides (MOSs), but its exact physiological role in plants is poorly understood. Here, we discover a specialized role of PHS1 in establishing the unique bimodal characteristic of starch granules in wheat (Triticum spp.) endosperm. Wheat endosperm contains large A-type granules that initiate at early grain development, and small B-type granules that initiate in later grain development. We demonstrate that PHS1 interacts with B-GRANULE CONTENT1 (BGC1), a carbohydrate-binding protein essential for normal B-type granule initiation. Mutants of tetraploid durum wheat (Triticum turgidum) deficient in all homoeologs of PHS1 had normal A-type granules but fewer and larger B-type granules. Grain size and starch content were not affected by the mutations. Further, by assessing granule numbers during grain development in the phs1 mutant and using a double mutant defective in both PHS1 and BGC1, we demonstrate that PHS1 is exclusively involved in B-type granule initiation. The total starch content and number of starch granules per chloroplast in leaves were not affected by loss of PHS1, suggesting that its role in granule initiation in wheat is limited to the endosperm. We therefore propose that the initiation of A- and B-type granules occurs via distinct biochemical mechanisms, where PHS1 plays an exclusive role in B-type granule initiation.

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“…There are numerous examples of altered granule morphology in wheat arising as a consequence of mutations in genes that affect starch polymer biosynthesis and structure (e.g. SS3 and SBE2) or granule initiation patterns (SS4, BGC1, and MRC) (Carciofi et al, 2012;Chia et al, 2020;Hawkins et al, 2021;Chen et al, 2022a;Fahy et al, 2022).…”

Section: Mutation Of Ttparc6 Increases Amyloplast Size and Alters Sta...mentioning

confidence: 99%

Modification of amyloplast size in wheat endosperm through mutation of PARC6 affects starch granule morphology

Esch

Ngai

Barclay

et al. 2023

Preprint

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Starch granule morphology is a major factor determining the functional and nutritional properties of starch. Here, we reveal amyloplast structure plays an important role in starch granule morphogenesis in wheat endosperm. Wheat amyloplasts contain large discoid A-type granules and small spherical B-type granules. We isolated a mutant in durum wheat defective in the plastid division protein PARC6, which had increased plastid size in both leaves and endosperm. Endosperm amyloplasts of the mutant contained more A- and B-type granules than those of the wild type. In mature grains, the mutant had larger A- and B-type granules than the wild type, and its A-type granules had a highly aberrant, lobed surface. This defect in granule morphology was already evident at early stages of grain development when granule size was identical between the mutant and the wild type, and occurred without obvious alterations in starch polymer structure and composition. Plant growth and photosynthetic efficiency, as well as the size, number and starch content of grains, were not affected in the Ttparc6 mutants despite the large changes in plastid size. Interestingly, mutation of the PARC6 paralog, ARC6, in durum wheat did not increase plastid or starch granule size. We suggest this is because TtPARC6 can complement disrupted TtARC6 function by interacting with PDV2, the outer plastid envelope protein that typically interacts with ARC6 to promote plastid division. We propose that amyloplast compartment size and available stromal volume play important roles in determining starch granule size, shape and number per amyloplast.

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Loss of starch synthase IIIa changes starch molecular structure and granule morphology in grains of hexaploid bread wheat

Cited by 15 publications

References 52 publications

Increasing amyloplast size in wheat endosperm through mutation of PARC6 affects starch granule morphology

Increasing amyloplast size in wheat endosperm through mutation of PARC6 affects starch granule morphology

Initiation of B-type starch granules in wheat endosperm requires the plastidial α-glucan phosphorylase PHS1

Modification of amyloplast size in wheat endosperm through mutation of PARC6 affects starch granule morphology

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