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 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.
Purpose Rhizosphere is the key part of belowground interaction between plant, microbes and soil. Beneficial interactions between plant roots and rhizosphere microorganisms are pivotal for plant fitness. Given the effort to improve sweetpotato phosphorus (P) efficiency, it is important to understand the adaptive strategies of sweetpotato rhizosphere under limited P availability. The aim of this study was to explore the variation of bacterial community and metabolite profiles of sweetpotato rhizosphere and their interactions under low P stress.Method Rhizosphere samples collected from sweetpotato (Shangshu 19) grown in long-term (41 years) application nitrogen (N) and potassium (K) fertilizers (NK) and N, P and K fertilizers (NPK) soils were analyzed the bacterial community and metabolite profiles by 16S rRNA high-throughput sequencing and liquid chromatography-mass spectrometry (LC-MS), respectively. Conclusion Different fertilization treatments significantly affected the abundances of rare genus in Shangshu 19 rhizosphere. The COG and KEGG enrichment analysis showed the function of bacterial correlated to sugar metabolism and inositol phosphate metabolism were significantly enhanced under low P stress. LC-MS analysis obtained similar results that galactose metabolism and phospholipase D signaling pathway were the top 2 differential metabolic pathways. Our results suggested that the bacteria of Shangshu 19 rhizosphere may use sugars as energy material to respond to low P stress by changing inositol phosphate metabolism. The increases of lipid-like substances played a connecting role, it was produced by sugar metabolism, and then entering mevalonate pathway activate inositol phosphate metabolism. These results have important practical significance for optimizing sweetpotato cultivation system.
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