Molecular Plant Breeding 2025, Vol.16, No.1, 73-81 http://genbreedpublisher.com/index.php/mpb 74 2 Background on Sweet Potato Genetics and Drought Tolerance 2.1 Genetic basis of drought tolerance in sweet potato Sweet potato (Ipomoea batatas [L.] Lam.) is a vital crop for food security, particularly in regions prone to drought. The genetic basis of drought tolerance in sweet potato involves complex interactions between various genes and environmental factors. Transcriptomic studies have identified numerous differentially expressed genes (DEGs) in response to drought stress, highlighting the importance of genetic regulation in drought tolerance. For instance, a study on the sweet potato cultivars Beauregard and Tanzania revealed that between 4 000 to 6 000 genes were differentially expressed under drought conditions, with many of these genes being associated with known drought response pathways (Lau et al., 2018; You et al., 2022). The overexpression of specific genes such as IbMIPS1 has been shown to enhance drought tolerance by regulating inositol biosynthesis and stress response pathways. 2.2 Key genes and pathways related to stress response Several key genes and pathways have been identified as crucial for drought tolerance in sweet potato. The WRKY transcription factors, particularly ItfWRKY70, play a significant role in enhancing drought tolerance by regulating abscisic acid (ABA) biosynthesis, stress-response genes, and reactive oxygen species (ROS) scavenging systems (Alvarez-Morezuelas et al., 2023). The IbMIPS1 gene is another critical gene that enhances drought tolerance by up-regulating genes involved in inositol biosynthesis, phosphatidylinositol (PI) signaling, and ABA signaling pathways (Zhai et al., 2016). Furthermore, transcriptomic analyses have identified genes involved in plant hormone transduction, MAPK signaling, and carbohydrate metabolism as essential for drought stress responses (Qin et al., 2022; Sun et al., 2022). These pathways collectively contribute to the plant's ability to withstand drought by modulating physiological and biochemical processes. 2.3 Natural variation and existing drought-resistant varieties Natural variation in drought tolerance among sweet potato cultivars provides a valuable resource for breeding programs. Studies have classified sweet potato cultivars into different groups based on their drought tolerance performance. For example, a comprehensive study on seven sweet potato cultivars identified distinct drought tolerance mechanisms, with some cultivars showing minimal impact from drought stress while others exhibited significant physiological and metabolic changes. The cultivar Xuzi-8, for instance, demonstrated extreme drought tolerance by primarily regulating cell wall components, whereas other cultivars like Chaoshu-1 and Z15-1 regulated flavonoid and carbohydrate metabolism to cope with drought (Figure 1) (Liu et al., 2023). These findings underscore the importance of leveraging natural genetic variation to develop drought-resistant sweet potato varieties through molecular breeding techniques. Figure 1 A corresponding working model of different drought tolerant sweet potato clutivars in response to drought. Red box indicate up-regulation, blue box indicate down-regulation (Adopted from Liu et al., 2023)
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