Cassava shrunken-2 homolog MeAPL3 determines storage root starch and dry matter content and modulates storage root posth
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Cassava shrunken‑2 homolog MeAPL3 determines storage root starch and dry matter content and modulates storage root postharvest physiological deterioration Getu Beyene1 · Raj Deepika Chauhan1 · Jackson Gehan1 · Dimuth Siritunga2 · Nigel Taylor1 Received: 19 December 2019 / Accepted: 5 March 2020 © The Author(s) 2020
Abstract Key message Among the five cassava isoforms (MeAPL1–MeAPL5), MeAPL3 is responsible for determining storage root starch content. Degree of storage root postharvest physiological deterioration (PPD) is directly correlated with starch content. Abstract AGPase is heterotetramer composed of two small and two large subunits each coded by small gene families in higher plants. Studies in cassava (Manihot esculenta) identified and characterized five isoforms of Manihot esculenta ADPglucose pyrophosphorylase large subunit (MeAPL1–MeAPL5) and employed virus induced gene silencing (VIGS) to show that MeAPL3 is the key isoform responsible for starch and dry matter accumulation in cassava storage roots. Silencing of MeAPL3 in cassava through stable transgenic lines resulted in plants displaying significant reduction in storage root starch and dry matter content (DMC) and induced a distinct phenotype associated with increased petiole/stem angle, resulting in a droopy leaf phenotype. Plants with reduced starch and DMC also displayed significantly reduced or no postharvest physiological deterioration (PPD) compared to controls and lines with high DMC and starch content. This provides strong evidence for direct relationships between starch/dry matter content and its role in PPD and canopy architecture traits in cassava. Keywords Cassava · ADP-glucose pyrophophorylase · MeAPL3 · Starch · Dry matter · Postharvest physiological deterioration
Introduction Cassava (Manihot esculenta Crantz) is widely grown for its starchy storage roots across the tropics and subtropics, with an estimated annual production of over 292 million metric tonnes (MT) in 2017 (FAOSTAT, accessed 12/17/2019). Africa accounts for 61% of this production, with Nigeria being the world’s largest producer at 59.4 million MT. Cassava is grown by 100 s millions of smallholder farmers as a subsistence crop. However, Electronic supplementary material The online version of this article (https://doi.org/10.1007/s11103-020-00995-z) contains supplementary material, which is available to authorized users. * Getu Beyene [email protected] 1
Donald Danforth Plant Science Center, St. Louis, MO, USA
Department of Biology, University of Puerto Rico, Mayaguez, Puerto Rico
2
dependence on the crop in sub-Saharan Africa is threatened by biotic stresses, especially cassava mosaic disease (CMD), cassava brown streak disease (CBSD), cassava bacterial blight (CBB) and cassava green mites (CGM) (Bull et al. 2011; Bart and Taylor 2017). Cassava production and utilization is also limited by inherent susceptibility of storage roots to rapid postharvest deterioration after removal from the soil (Beeching et al. 1998). This commences 24–48 h after
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