Plants can adapt to the spatial heterogeneity of soil nutrients by changing the morphology and architecture of the root system. Here, we explored the role of auxin in the response of sweetpotato roots to potassium (K⁺) deficiency stress. Two sweetpotato cultivars, Xushu 32 (low-K-tolerant) and Ningzishu 1 (low-K-sensitive), were cultured in low K⁺ (0.1 mmol L⁻¹, LK) and normal K⁺ (10 mmol L⁻¹, CK) nutrient solutions. Compared with CK, LK reduced the dry mass, K⁺ content, and K⁺ accumulation in the two cultivars, but the losses of Xushu 32 were smaller than those of Ningzishu 1. LK also affected root growth, mainly impairing the length, surface area, forks number, and crossings number. However, Xushu 32 had significantly higher lateral root length, density, and surface area than Ningzishu 1, closely related to the roots’ higher indole-3-acetic acid (IAA) content. According to the qPCR results, Xushu 32 synthesized more IAA (via IbYUC8 and IbTAR2) in leaves but transported and accumulated in roots through polar transport (via IbPIN1, IbPIN3, and IbAUX1). It was also associated with the upregulation of auxin signaling pathway genes (IbIAA4 and IbIAA8) in roots. These results imply that IAA participates in the formation of lateral roots and the change in root architecture during the tolerance to low K⁺ stress of sweetpotato, thus improving the absorption of K⁺ and the formation of biomass.

The high-affinity potassium transporters (HKT) mediate K⁺-Na⁺ homeostasis in plants. However, the function of enhancing low-potassium tolerance in sweet potato [Ipomoea batatas (L.) Lam.] remains unrevealed. In this study, a novel HKT transporter homolog IbHKT-like gene was cloned from sweet potato, which was significantly induced by potassium deficiency stress. IbHKT-like overexpressing transgenic roots were obtained from a sweet potato cultivar Xuzishu8 using an Agrobacterium rhizogenes-mediated root transgenic system in vivo. Compared with the CK, whose root cells did not overexpress the IbHKT-like gene, overexpression of the IbHKT-like gene protected cell ultrastructure from damage, and transgenic root meristem cells had intact mitochondria, endoplasmic reticulum, and Golgi dictyosomes. The steady-state K⁺ influx increased by 2.2 times in transgenic root meristem cells. Overexpression of the IbHKT-like gene also improved potassium content in the whole plant, which increased by 63.8% compared with the CK plants. These results could imply that the IbHKT-like gene, as a high-affinity potassium transporter gene, may play an important role in potassium deficiency stress responses.

The sweet potato is very sensitive to low temperature. Our previous study revealed that IbMPK3-overexpressing transgenic sweet potato (M3) plants showed stronger low-temperature stress tolerance than wild-type plants (WT). However, the mechanism of M3 plants in response to low-temperature stress is unclear. To further analyze how IbMPK3 mediates low-temperature stress in sweet potato, WT and M3 plants were exposed to low-temperature stress for 2 h and 12 h for RNA-seq analysis, whereas normal conditions were used as a control (CK). In total, 3436 and 8718 differentially expressed genes (DEGs) were identified in WT at 2 h (vs. CK) and 12 h (vs. CK) under low-temperature stress, respectively, whereas 1450 and 9291 DEGs were detected in M3 plants, respectively. Many common and unique DEGs were analyzed in WT and M3 plants. DEGs related to low temperature were involved in Ca²⁺ signaling, MAPK cascades, the reactive oxygen species (ROS) signaling pathway, hormone transduction pathway, encoding transcription factor families (bHLH, NAC, and WRKY), and downstream stress-related genes. Additionally, more upregulated genes were associated with the MAPK pathway in M3 plants during short-term low-temperature stress (CK vs. 2 h), and more upregulated genes were involved in secondary metabolic synthesis in M3 plants than in the WT during the long-time low-temperature stress treatment (CK vs. 12 h), such as fatty acid biosynthesis and elongation, glutathione metabolism, flavonoid biosynthesis, carotenoid biosynthesis, and zeatin biosynthesis. Moreover, the interaction proteins of IbMPK3 related to photosynthesis, or encoding CaM, NAC, and ribosomal proteins, were identified using yeast two-hybrid (Y2H). This study may provide a valuable resource for elucidating the sweet potato low-temperature stress resistance mechanism, as well as data to support molecular-assisted breeding with the IbMPK3 gene.

Black rot disease, caused by Ceratocystis fimbriata Ellis & Halsted, severely affects both plant growth and post-harvest storage of sweet potatoes. Invertase (INV) enzymes play essential roles in hydrolyzing sucrose into glucose and fructose and participate in the regulation of plant defense responses. However, little is known about the functions of INV in the growth and responses to black rot disease in sweet potato. In this study, we identified and characterized an INV-like gene, named IbINV, from sweet potato. IbINV contained a pectin methylesterase-conserved domain. IbINV transcripts were most abundant in the stem and were significantly induced in response to C. fimbriata, salicylic acid, and jasmonic acid treatments. Overexpressing IbINV in sweet potato (OEV plants) led to vigorous growth and high resistance to black rot disease, while the down-regulation of IbINV by RNA interference (RiV plants) resulted in reduced plant growth and high sensitivity to black rot disease. Furthermore, OEV plants contained a decreased sucrose content and increased hexoses content, which might be responsible for the increased INV activities; not surprisingly, RiV plants showed the opposite effects. Taken together, these results indicate that IbINV positively regulates plant growth and black rot disease resistance in sweet potato, mainly by modulating sugar metabolism.

Purple-fleshed sweet potato (PFSP) (Ipomoea batatas) is a rich source of anthocyanins, which serve as potent antioxidants and contribute to stress tolerance. However, the molecular mechanisms regulating anthocyanin biosynthesis in PFSP under phosphorus stress remain poorly understood. In this study, integrated transcriptomic and metabolomic analyses were conducted using the sweet potato cultivar (Xuzishu No. 8) grown under three phosphorus treatments: XP0 (0 g), XP1 (1.85 g), and XP2 (3.70 g). Although phosphorous did not significantly affect total anthocyanin content, however, marked changes were observed in the activities of key biosynthetic enzymes (CHl, DFR, OPC, PAL and UFGT). RNA-seq analysis identified 8,906 differentially expressed genes (DEGs) with 11,215 novel genes across the treatments. KEGG pathway enrichment analysis revealed that most DEGs were associated phenylpropanoid biosynthesis. Metabolomic profiling detected 110 differentially expressed metabolites (DEMs) among which six were common to all treatments and sixteen metabolites were shared between the treatment groups. Functional annotation of DEMs indicated an overall suppression of anthocyanin biosynthesis pathway, across the treatments, whereas, flavone and flavonol biosynthesis remained consistently active. Notably, Quercetin-3-O-glucoside appeared to play a key role in the restoring anthocyanin biosynthesis. Integrated transcriptome-metabolome analysis showed a strong coordinated regulation between DEGs and DEMs, particularly within anthocyanin and flavonoid biosynthetic pathways. Furthermore, Canonical correspondence analysis (CCA) and principal component analysis (PCA) biplot further revealed that anthocyanin accumulation is controlled by the combined action of multiple genes, with Tai6.6720 identified as a key regulatory gene closely linked with active metabolites (Pelargonidin-3-O- glucoside and cyanidin-3-O- glucoside). Overall, these findings highlight the significant impact of phosphorous stress on transcriptional and metabolic reprogramming of anthocyanin biosynthesis as an adaptive response. This study provides new insights on the regulatory networks that control anthocyanin accumulation in sweet potato and offers a valuable foundation for nutrient management strategies and molecular breeding approaches to improve crop stress tolerance.

Sweetpotato (Ipomoea batatas (L.) Lam.) is a vital global food crop whose production and geographical distribution are severely constrained by low-temperature stress. While WRKY transcription factors are known to regulate plant stress responses, their specific roles in sweetpotato cold tolerance remain largely unexplored. In this study, we conducted a genome-wide identification of the WRKY family in the hexaploid sweetpotato genome, identifying 476 IbWRKYs classified into three major groups and seven subgroups. Synteny analyses revealed that whole-genome duplication (WGD)/segmental duplication (SD) was the primary mode of gene duplication for this conserved family. To identify key cold-responsive regulators, we evaluated the cold tolerance phenotypes of 232 diverse accessions and performed comparative transcriptome profiling on representative cold-tolerant and cold sensitive cultivars. Integrated transcriptomic and co-expression network analyses highlighted IbWRKY460 as a leading cold-responsive candidate. Quantitative RT-PCR confirmed its cold-induced expression, the GFP fusion protein localized to the nucleus, and heterologous expression in yeast provided preliminary evidence of protective activity during low-temperature exposure. Together, these findings prioritize IbWRKY460 for in-planta functional validation and provide a genomic framework for investigating cold-responsive WRKY genes in sweetpotato.