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Sweet potato is an important plant for researchers to study storage root development and resistance. MADS‐box proteins are a group of important transcription factors which play a crucial role in plant development as well as stress response. However, the investigation regarding sweet potato MADS‐box genes remains limited up to now. In this study, nine MADS‐box genes, named as IbMBP1˜IbMBP9, were cloned and characterized. Nine genes exhibited different tissue‐specific expression profiles. IbMBP2, IbMBP3, IbMBP4 and IbMBP9 showed high expression during storage roots development and were upregulated by storage roots development‐related hormones. Varying degrees of induction was observed in the transcript level of these MADS‐box genes under multiple abiotic stresses, as well as stress‐related hormones. The present results revealed that nine MADS‐box genes exhibited different tissue‐specific expression profiles and were impacted by multiple abiotic stresses and/or hormones, which lay a good foundation for further exploring the function of MADS‐box genes in sweet potato.

Plant C2-domain abscisic acid-related (CAR) protein family plays an important role in plant growth, abiotic stress responses, and defense regulation. In this study, we cloned the IbCAR1 by homologous cloning method from the transcriptomic data of Xuzishu8, which is a sweet potato cultivar with dark-purple flesh. This gene was expressed in all tissues of sweet potato, with the highest expression level in leaf tissue, and it could be induced by NaCl and ABA. Subcellular localization analyses indicated that IbCAR1 was localized in the nucleus and plasma membrane. The PI staining experiment revealed the distinctive root cell membrane integrity of overexpressed transgenic lines upon salt stress. Salt stress significantly increased the contents of proline, ABA, and the activity of superoxide dismutase (SOD), whereas the content of malondialdehyde (MDA) was decreased in overexpressed lines. On the contrary, RNA interference plants showed sensitivity to salt stress. Overexpression of IbCAR1 in sweet potatoes could improve the salt tolerance of plants, while the RNAi of IbCAR1 significantly increased sensitivity to salt stress in sweet potatoes. Meanwhile, the genes involved in ABA biosynthesis, stress response, and reactive oxygen species (ROS)-scavenging system were upregulated in overexpressed lines under salt stress. Taken together, these results demonstrated that IbCAR1 plays a positive role in salt tolerance by relying on the ABA signal transduction pathway, activating the ROS-scavenging system in sweet potatoes.

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