Contrasting roles of the wheat MRC in promoting starch granule initiation in leaves and repressing the onset of B-type granule initiation in the endosperm

Chen, J.; Chen, Y.; Watson-Lazowski, A.; Hawkins, E.; Barclay, J. E.; Fahy, B.; Denley-Bowers, R.; Corbin, K.; Warren, F. J.; Blennow, A.; Uauy, C.; Seung, D.

doi:10.1101/2022.10.07.511297

bioRxiv · 10.1101/2022.10.07.511297

Contrasting roles of the wheat MRC in promoting starch granule initiation in leaves and repressing the onset of B-type granule initiation in the endosperm

Chen, J.·Chen, Y.·Watson-Lazowski, A.·Hawkins, E.·Barclay, J. E.·Fahy, B.·Denley-Bowers, R.·Corbin, K.·Warren, F. J.·Blennow, A.·Uauy, C.·Seung, D.

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Abstract

The spatial and temporal patterns by which starch granules initiate vary greatly between species and organs, but molecular factors that contribute to these diverse patterns are poorly understood. We reveal distinct organ-specific roles of the MYOSIN-RESEMBLING CHLOROPLAST PROTEIN (MRC) in regulating granule initiation in the endosperm and leaves of wheat. We isolated three independent TILLING mutants of tetraploid wheat (Triticum turgidum cv. Kronos) with premature stop or missense mutations in the A-genome homeolog, which we showed to be the only active homeolog in tetraploid wheat due to a disruption of the B-genome homeolog. Wheat endosperm contains both large A-type granules initiated during early grain development, and small B-type granules that initiate about 10 - 15 days later. The mrc mutants had significantly smaller A-type granules and a higher relative volume of B-type granules in the endosperm than the wild type. Whereas B-type granules initiated 15 - 20 days post anthesis (dpa) in the wild-type, they appeared as early as 10 dpa in the mrc-1 mutant, suggesting a role for MRC in suppressing B-type granule initiation during early grain development. By contrast, MRC promotes granule initiation in leaves: mutants carrying premature stop mutations in MRC had fewer granules per chloroplast than the wild type. These contrasting roles of MRC among wheat organs provide new insight into functional diversification of granule initiation proteins, and suggest that they may facilitate the diverse patterns of granule initiation observed across species and organs.

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Chen, J., Chen, Y., Watson-Lazowski, A., Hawkins, E., Barclay, J. E., Fahy, B., Denley-Bowers, R., Corbin, K., Warren, F. J., Blennow, A., Uauy, C., Seung, D.. 2022-10-07. Contrasting roles of the wheat MRC in promoting starch granule initiation in leaves and repressing the onset of B-type granule initiation in the endosperm. https://doi.org/10.1101/2022.10.07.511297

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