Malate dehydrogenase (MDH; EC 1.1.1.37) plays a vital role in plant growth and development as well as abiotic stress responses, and it is widely present in plants. However, the MDH family genes have not been explored in sweet potato. In this study, nine, ten, and ten MDH genes in sweet potato (Ipomoea batatas) and its two diploid wild relatives, Ipomoea trifida and Ipomoea triloba, respectively, were identified. These MDH genes were unevenly distributed on seven different chromosomes among the three species. The gene duplications and nucleotide substitution analysis (Ka/Ks) revealed that the MDH genes went through segmental duplications during their evolution under purifying selection. A phylogenetic and conserved structure divided these MDH genes into five subgroups. An expression analysis indicated that the MDH genes were omni-presently expressed in distinct tissues and responded to various abiotic stresses. A transcription factor prediction analysis proved that Dof, MADS-box, and MYB were the main transcription factors of sweet potato MDH genes. These findings provide molecular features of the MDH family in sweet potato and its two diploid wild relatives, which further supports functional characterizations.

In this study, genome-wide characterization of F-box proteins in sweet potato yielded 243 IbFBX genes, unevenly distributed on the 15 chromosomes of sweet potato. Gene duplication analysis suggested segmental duplication as the principal factor influencing the expansive evolution of IbFBX genes in sweet potato. Phylogenetic analysis clustered F-box proteins in sweet potato, Arabidopsis, and rice into six clades (I-VI). Gene structure analysis of the IbFBX genes revealed that most of the genes within the same clade were highly conserved. Expression profiles of IbFBX family genes in 9 different tissues and under stress conditions revealed that the IbFBXs were highly upregulated or downregulated in response to salt and drought stress, suggesting their significant roles in abiotic stress response and adaptation. Knowledge of the diverse functions and expression patterns of IbFBXs presents a solid theoretical basis for annotating the functions of IbFBXs and further facilitate the molecular breeding of sweet potato.

The LBD family is a plant-specific transcription factor family that plays an important role in a variety of biological processes. However, the function of IbLBD genes in sweet potato remains unclear. In this study, we identified a total of 53 IbLBD genes in sweet potato. Genetic structure showed that most of the IbLBD genes contained only two exons. Following the phylogenetic investigation, the IbLBD gene family was separated into Class I (45 members) and Class II (8) members. Both classes of proteins contained relatively conservative Motif1 and Motif2 domains. The chromosomal locations, gene duplications, promoters, PPI network, and GO annotation of the sweet potato LBD genes were also investigated. Furthermore, gene expression profiling and real-time quantitative PCR analysis showed that the expression of 12 IbLBD genes altered in six separate tissues and under various abiotic stresses. The IbLBD genes belonging to Class I were mostly expressed in the primary root, the pencil root, and the leaves of sweet potatoes, while the genes belonging to Class II were primarily expressed in the various sweet potato roots. The IbLBD genes belonging to Class I were mostly expressed in the primary root, the pencil root, and the leaves of sweet potatoes, while the genes belonging to Class II were primarily expressed in the fibrous root, pencil root, and tuber root.

The starch synthase (SS) plays important roles in regulating plant growth and development and responding to adversity stresses. Although the SS family has been studied in many crops, it has not been fully identified in sweet potato and its two related species. In the present study, eight SSs were identified from Ipomoea batatas (I. batata), Ipomoea trifida (I. trifida), and Ipomoea trlioba (I. trlioba), respectively. According to the phylogenetic relationships, they were divided into five subgroups. The protein properties, chromosomal location, phylogenetic relationships, gene structure, cis-elements in the promoter, and interaction network of these proteins were also analyzed; stress expression patterns were systematically analyzed; and real-time polymerase chain reaction (qRT-PCR) analysis was performed. Ipomoea batatas starch synthase (IbSSs) were highly expressed in tuber roots, especially Ipomoea batatas starch synthase 1 (IbSS1) and Ipomoea batatas starch synthase 6 (IbSS6), which may play an important role in root development and starch biosynthesis. At the same time, the SS genes respond to potassium deficiency, hormones, cold, heat, salt, and drought stress. This study offers fresh perspectives for enhancing knowledge about the roles of SSs and potential genes to enhance productivity, starch levels, and resistance to environmental stresses in sweet potatoes.

Growth-regulating factor (GRF) is a multi-gene family that plays an important role in plant growth and development and is widely present in plants. Currently, GRF gene members have been reported in many plants, but the GRF gene family has not been found in sweet potato. In this study, ten GRF genes were identified in sweet potato (Ipomoea batatas), twelve and twelve were identified in its two diploid relatives (Ipomoea trifida) and (Ipomoea triloba), which were unevenly distributed on nine different chromosomes. Subcellular localization analysis showed that GRF genes of sweet potato, I. trifida, and I. triloba were all located in the nucleus. The expression analysis showed that the expression of IbGRFs was diverse in different sweet potato parts, and most of the genes were upregulated and even had the highest expression in the vigorous growth buds. These findings provide molecular characterization of sweet potato and its two diploid relatives, the GRF families, further supporting functional characterization.