Yufeng Yang

Background: Protein phosphatase 2 C (PP2C) proteins play crucial roles in plant growth, development, and stress responses. However, PP2C gene family members in Ipomoea trifida (wild relative of sweet potato) have not been comprehensively investigated, thereby limiting our understanding of their functions. Results: We identified 91 PP2C genes ( ItfPP2C1–91 ) that were unevenly distributed across all 15 I. trifida chromosomes. On the basis of a phylogenetic analysis, these genes were classified into 13 subfamilies, with subfamilies E, A, and D containing the most genes. Conserved motif and gene structure analyses revealed subfamily-specific patterns, with motif 2 identified as the most conserved motif. Numerous promoter cis-acting elements related to hormone responses and stress tolerance were identified. Tissue-specific ItfPP2C expression patterns were observed, with several genes expressed at high levels in all examined tissues, while other genes were expressed in specific tissues. Under drought conditions, most PP2C genes had upregulated expression levels, with significant increases in ItfPP2C15 , 16 , 30 , and 77 (subfamily A) expression suggesting that they may be key drought-responsive candidate genes. In response to a stem nematode infection, ItfPP2C30 , ItfPP2C77 , and ItfPP2C89 were differentially expressed between resistant and susceptible varieties. Moreover, ItfPP2C90 expression was significantly induced in Z22 and L9 at 12 h. Hence, these genes may be involved in disease resistance. A protein interaction network analysis identified proteins that may interact with ItfPP2C30 and ItfPP2C77, most of which were ABA receptors (PYLs) and kinases (SnRK2s). Conclusions: Our comprehensive analysis of the PP2C gene family in I. trifida provides valuable insights into their evolutionary relationships, structural features, and potential functions related to growth and stress responses. ItfPP2C30 and ItfPP2C77 were identified as promising candidates for improving both drought and nematode resistance, with the encoded proteins potentially interacting with PYL and SnRK2 proteins in stress-related signaling pathways.

Stem nematode disease, the most prevalent of three major diseases in northern China, causes huge sweet potato production losses. In this study, the resistant (Zhenghong22) and sensitive (Longshu9) parents, and the F₁ segregating population mixed pools (Resistant- and Sensitive-Mixed) having extreme resistance traits, were used for BSA-Seq, BSR-Seq, and transcriptomic analyses to locate stem nematode disease resistance-conferring genes in sweet potato. Transcriptome results indicated that ethylene and ABA were the main hormones involved in disease resistance regulation, with secondary metabolic pathways playing crucial roles. In total, 7 and 17 candidate regions, which contained 743 candidate genes, were identified in the BSA-Seq and BSR-Seq analyses, respectively. Eight candidate genes were identified using a combined analysis. The protein phosphatase 2C gene itf15g20460, the signal transduction-related gene itf00g76200, and an unknown functional gene itf00g75950, were identified as key resistance gene candidates through RT-qPCR validation in mixed pools and individuals. These results will be beneficial to the cultivation of nematode-resistant sweet potato cultivars.

Sweet potato (Ipomoea batatas (L.) Lam.) is one of the most widely cultivated crops in the world, with outstanding stress tolerance, but drought stress can lead to a significant decrease in its yield. To reveal the response mechanism of sweet potato to drought stress, an integrated physiological, transcriptome and metabolome investigations were conducted in the leaves of two sweet potato varieties, drought-tolerant zhenghong23 (Z23) and a more sensitive variety, jinong432 (J432). The results for the physiological indexes of drought showed that the peroxidase (POD) and superoxide dismutase (SOD) activities of Z23 were 3.68 and 1.21 times higher than those of J432 under severe drought, while Z23 had a higher antioxidant capacity. Transcriptome and metabolome analysis showed the importance of the amino acid metabolism, respiratory metabolism, and antioxidant systems in drought tolerance. In Z23, amino acids such as asparagine participated in energy production during drought by providing substrates for the citrate cycle (TCA cycle) and glycolysis (EMP). A stronger respiratory metabolism ability could better maintain the energy supply level under drought stress. Drought stress also activated the expression of the genes encoding to antioxidant enzymes and the biosynthesis of flavonoids such as rutin, resulting in improved tolerance to drought. This study provides new insights into the molecular mechanisms of drought tolerance in sweet potato.

Sweetpotato is a heliophile crop. However, it is usually shaded in the lower position in the interplanting cultivation mode. During the middle and late field growing period, it often faces rainy weather with little illumination, which affects the dry matter accumulation in tuberous roots. Thus, analyzing the metabolic response pathways of sweetpotato under shade stress will provide the theoretical basis for the varieties’ genetic improvement of shade tolerance. In this study, the sweetpotato variety Zhenghong 23 was exposed to shade stress with 50% light transmittance for 15 days. Results showed that chlorophyll b and the total chlorophyll contents of Zhenghong 23 under shade stress were significantly increased compared with those under natural light. The maximum photochemical efficiency (Fv/Fm), the potential activity (Fv/Fo), and the comprehensive index of photosynthetic performance (PIABS) of the chlorophyll photosystem PSII decreased significantly under shade stress. The net photosynthetic rate and water use efficiency decreased significantly, while SOD and POD enzyme activities increased significantly. In addition, shade stress increased significantly the vine length and specific leaf area of Zhenghong 23, but reduced significantly the fresh weight of roots. Transcriptome and metabolome analysis of leaf tissues under shade stress and natural light conditions showed that the DEGs and DMs were mainly enriched in phenylpropanoid biosynthesis, sugar metabolism, sphinolipid metabolism, and arginine biosynthesis pathways. Most of the up-regulated DEGs enriched in the phenylpropanoid biosynthesis pathway were POD enzyme family genes, indicating that the shade stress triggered the ROS scavenging system in sweetpotato. Meanwhile, shade stress reduced sugar metabolism level of sweetpotato, decreased the soluble sugar content of leaves, inhibited both the synthesis and degradation of starch, and blocked the expansion of tuberous roots. In addition, the sphinolipid and arginine metabolism pathways may better adapt sweetptoato plants to shade stress through improving the stability of biomembranes and increase the synthetic substrates of polyamine anti-stress factors. These results provide new theoretical basis for understanding the metabolic response pathways of sweetpotato under shade stress.

Stem nematode disease can seriously reduce the yield of sweet potato (Ipomoea batatas (L.) Lam). To explore resistance mechanism to stem nematode in sweet potato, transcriptomes and metabolomes were sequenced and compared between two sweet potato cultivars, the resistant Zhenghong 22 and susceptible Longshu 9, at different times after stem nematode infection. In the transcriptional regulatory pathway, mitogen-activated protein kinase signaling was initiated in Zhenghong 22 at the early stage of infection to activate genes related to ethylene production. Stem nematode infection in Zhenghong 22 also triggered fatty acid metabolism and the activity of respiratory burst oxidase in the metabolic pathway, which further stimulated the glycolytic and shikimic pathways to provide raw materials for secondary metabolite biosynthesis. An integrated analysis of the secondary metabolic regulation pathway in the resistant cultivar Zhenghong 22 revealed the accumulation of tryptophan, phenylalanine, and tyrosine, leading to increased biosynthesis of phenylpropanoids and salicylic acid and enhanced activity of the alkaloid pathway. Stem nematode infection also activated the biosynthesis of terpenoids, abscisic acid, zeatin, indole, and brassinosteroid, resulting in improved resistance to stem nematode. Finally, analyses of the resistance regulation pathway and a weighted gene co-expression network analysis highlighted the importance of the genes itf14g17940 and itf12g18840, encoding a leucine-rich receptor-like protein and 1-aminocyclopropane-1-carboxylate synthase, respectively. These are candidate target genes for increasing the strength of the defense response. These results provide new ideas and a theoretical basis for understanding the mechanism of resistance to stem nematode in sweet potato.

Sweet potato (Ipomoea batatas), an important root crop, has storage roots rich in starch that are edible and serve as a raw material in bioenergy production. Increasing the storage-root starch contents is a key sweet potato breeding goal. Phosphoglucomutase (PGM) is the catalytic enzyme for the interconversion of glucose-6-phosphate and glucose-1-phosphate, precursors in the plant starch synthetic pathway. Plant PGMs have plastidial and cytosolic isoforms, based on their subcellular localization. Here, IbpPGM, containing 22 exons and 21 introns, was cloned from the sweet potato line Xu 781. This gene was highly expressed in the storage roots and leaves, and its expression was induced by exogenous sucrose treatments. The mature IbpPGM protein was successfully expressed in Escherichia coli when a 73-aa chloroplastic transit peptide detected in the N-terminus was excised. The subcellular localization confirmed that IbpPGM was localized to the chloroplasts. The low-starch sweet potato cultivar Lizixiang IbpPGM-overexpression lines showed significantly increased starch, glucose, and fructose levels but a decreased sucrose level. Additionally, the expression levels of the starch synthetic pathway genes in the storage roots were up-regulated to different extents. Thus, IbpPGM significantly increased the starch content of the sweet potato storage roots, which makes it a candidate gene for the genetic engineering of the sweet potato.

WRKY transcription factors are one of the important families in plants, and have important roles in plant growth, abiotic stress responses, and defense regulation. In this study, we isolated a WRKY gene, ItfWRKY70, from the wild relative of sweet potato Ipomoea trifida (H.B.K.) G. Don. This gene was highly expressed in leaf tissue and strongly induced by 20% PEG6000 and 100 μM abscisic acid (ABA). Subcellar localization analyses indicated that ItfWRKY70 was localized in the nucleus. Overexpression of ItfWRKY70 significantly increased drought tolerance in transgenic sweet potato plants. The content of ABA and proline, and the activity of SOD and POD were significantly increased, whereas the content of malondialdehyde (MDA) and H₂O₂ were decreased in transgenic plants under drought stress. Overexpression of ItfWRKY70 up-regulated the genes involved in ABA biosynthesis, stress-response, ROS-scavenging system, and stomatal aperture in transgenic plants under drought stress. Taken together, these results demonstrated that ItfWRKY70 plays a positive role in drought tolerance by accumulating the content of ABA, regulating stomatal aperture and activating the ROS scavenging system in sweet potato.