Improving Starch-Related Traits in Potato Crops: Achievements and Future Challenges Sulaiman Ahmed, Xin Zhou, Yuehan Pang, Liping Jin, and Jinsong Bao* Potato is one of the most important starch crops in the world and is used as a staple food for more than one billion people worldwide. Starch is the main storage compound in potato tubers and is of considerable value in food and non-food applications. The starch biosynthesis pathway is the principal biochemical pathway in plants. Potato starch bioengineering can be consid- ered complicated and has been an extensive subject of study over the past three decades. Tetraploid inheritance is the most conspicuous feature linked with potato breeding. Genetic map construction and linkage mapping have contributed greatly to potato breeding, and association studies have further enhanced our knowledge to carry out optimized and comprehensive breeding programes. This review begins with the introduction of the starch structure with respect to functionality, the starch biosynthesis pathway and related genes/enzymes participating in the pathway. Then, the advances that have been made during the past years in the study of genetic basis of starch- related traits by linkage and association mapping are summarized. Molecular breeding via transgenic engineering of starch biosynthesis-related genes to modify starch properties is also reviewed. Finally, future challenges and new directions for improving starch quality in potato and the implication of new genome editing tools to produce the next generation starches are proposed. A better understanding of these factors is necessary to conduct molecular breeding programes in potato to improve starch quality. 1. Introduction Potato (Solanum tuberosum L.) is one of our most important starch crops and is widely used as a staple food throughout the world. Because potato germplasm cannot be stored as seeds and due to its polyploidy and very complex genetic inheritance, [1] potato starch bioengineering can be con- sidered complicated. Starch is the major storage compound in potato tubers, rang- ing from 10% to 25% of its fresh weight. [2] For industrial applications, tuber starch content (TSC) and starch yield (SY), i.e., starch produced per unit area, are consid- ered the most important production pa- rameters. Likewise, yield expressed as tuber yield (TY), TSC, and sugar contents are metabolically connected with carbohy- drate metabolism. [3] The economic impor- tance of the potato crop is also based on tubers, which are physiologically and metabolically specialized structures for the accumulation of starch. Starch accu- mulation is a complex developmental process that depends on the interaction of environmental, biochemical, and genetic factors. [4] The characteristics of starch, such as apparent amylose content (AAC), thermal properties, pasting properties, mean diameter, size, and distribution of granules, are considered important traits for determining starch quality. [5] Under- standing the molecular basis of SY and quality facilitates the breeding process in potato improvement programes by quickly pyramiding the superior alleles with the aid of molecular markers. Different biochemical pathways that are involved in the synthesis, degradation, and transport of carbohydrates are very well studied in plants. Quantitative trait loci (QTL) analysis is a routine approach to investigate the genetic control of complex agronomic and quality traits in crop plants, including potato. QTLs for TSC have been mapped using molecular markers, [6,7] as well as functional markers derived from genes responsible for carbohydrate metabolism and transport. [8] Natural varia- tions in the candidate genes have been used to test their association with tuber quality traits in tetraploid potato. [9] Molecular cloning and functional characterization of many genes have been performed to date for starch biosynthesis (e.g., ADP-glucose pyrophosphorylase [AGPase], starch synthases [SS], and starch branching enzymes [SBEs]), starch degradation (starch phosphorylases, debranching enzyme, and α-amylase), sucrose metabolism (sucrose phosphate synthase, sucrose synthases, and invertases), and transport (sucrose transporters). [7,8] Dr. S. Ahmed, Dr. X. Zhou, Dr. Y. Pang, Dr. J. Bao Institute of Nuclear Agricultural Science College of Agriculture and Biotechnology Zhejiang University Huajiachi Campus Hangzhou 310029, China E-mail: jsbao@zju.edu.cn Dr. L. Jin Department of Potato, Institute of Vegetables and Flowers Chinese Academy of Agricultural Sciences Beijing 100081, China Dr. L. Jin, Dr. J. Bao Key Laboratory of Biology and Genetic Improvement of Tuber and Root Crop Ministry of Agriculture Beijing 100081, P.R. China DOI: 10.1002/star.201700113 Potatoes www.starch-journal.com REVIEW Starch - Stärke 2018, 70, 1700113 © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim 1700113 (1 of 13)