The impact of the indica rice SSIIa allele on the apparent high amylose starch from rice grain with downregulated japoni
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ORIGINAL ARTICLE
The impact of the indica rice SSIIa allele on the apparent high amylose starch from rice grain with downregulated japonica SBEIIb Jixun Luo1,2 · Vito M. Butardo Jr.1,3 · Qiang Yang1,4,5 · Christine Konik‑Rose1 · Michelle L. Colgrave6 · Anthony Millar2 · Stephen A. Jobling1 · Zhongyi Li1 Received: 8 April 2020 / Accepted: 1 July 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract Key message Catalytically active indica SSIIa allele in high amylose rice with down-regulated japonica SBEIIb can increase starch content and modify the starch structure and properties without changing its amylose content. Abstract Rice (Oryza sativa) genotypes with inactive starch synthase IIa (SSIIa) with recessive variants of starch branching enzyme IIb (SBEIIb) exhibit a range of alterations in grain phenotype, starch granule morphology, starch granule bound proteins, starch structure, and functional properties. However, the interactions between the two enzymes have not been thoroughly investigated yet. We analysed recombinant rice lines having down-regulated SBEIIb expression (SBEIIb DR) with either indica or japonica type SSIIa (SSIIaind or SSIIajap). In SBEIIbDR rice starch granules, the increased abundance of two protein bands (SSI and SSIIa) was found with eight additional protein bands not generally associated with starch granules. The amount of SSIIa was higher in SSIIaindSBEIIbDR than SSIIajapSBEIIbDR, which indicated that indica type SSIIa, possibly in the monomer form, was extensively involved in starch biosynthesis in the SBEIIbDR endosperm. Furthermore, SSIIaindSBEIIbDR grains had higher total starch content and higher starch swelling power than SSIIajapSBEIIbDR lines, but the amylopectin gelatinization temperatures and enthalpy and the apparent amylose content remained similar. In summary, this work suggests that SSIIaind can partly compensate for the alteration of starch synthesis resulting from the SBEIIb downregulation in japonica background without reducing its amylose content. The study provides insight into the starch structural and textural improvements of high amylose starch.
Communicated by Takuji Sasaki. Electronic supplementary material The online version of this article (https://doi.org/10.1007/s00122-020-03649-2) contains supplementary material, which is available to authorized users. * Zhongyi Li [email protected] 1
CSIRO Agriculture and Food, GPO Box 1700, Canberra, ACT 2601, Australia
2
Research School of Biology, Australian National University, Canberra, ACT 0200, Australia
3
Faculty of Science, Engineering and Technology, Swinburne University of Technology, Hawthorn, VIC 3122, Australia
4
State Key Laboratory of Crop Gene Exploration and Utilization in Southwest China, Sichuan Agricultural University, Chengdu 611130, Sichuan, China
5
Triticeae Research Institute, Sichuan Agricultural University, Chengdu 611130, Sichuan, China
6
CSIRO Agriculture and Food, 306 Carmody Rd, St Lucia, QLD 4067, Australia
Background Amylose and amylop
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