Physiological and molecular responses of Trollius chinensis seedlings to waterlogging stress and subsequent drainage

Waterlogging led by extreme rainfall events is one of the major natural disasters under the global climate change context, putting plants under water stress. However, systematical studies on the response mechanisms in leaves to waterlogging are limited. We explored major leaf characteristics of oxidative stress and scavenging, photosynthesis, and osmotic regulations of Trollius chinensis. Two levels of waterlogging serverities (moderate level, W1, and severe level, W2) were studied on the 1st (D1), 5th (D5), 10th (D10), and 15th day (D15) upon waterlogging and on the subsequent 10th day after drainage (R10). In addition, based on physiological indicators, the leaves in control and W2 on D10 were selected for RNA-Seq. We found that most of physiological characteristics presented the greatest differences between control and waterlogging groups on D10 such as O-2(.-), SOD, and proline, while some other characteristics such as H2O2, POD, and GR showed highest change from control on D15. Furthermore, on R10, most of the physiologcial characteristics recovered in different levels, which indicates that this species is relative waterlogging-tolerant. The results also showed that out of 1182 differentially expressed genes (307 up-regulated and 875 down-regulated) obtained in W2 vs control, 'photosynthesis', 'plastid', 'chloroplast', 'thylakoid', and 'chlorophyll-binding' were the Gene Ontology (GO) enrichment hotspots, and 'photosynthesis', 'photosynthesis-antenna proteins', and 'carbon fixation in photosynthetic organisms' were the most enriched Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways. The expression of genes related to the photosynthesis, amylase, calcineurin interacting protein kinases (CIPKs), glutathione-S-transferase (GST), and ethylene response factor (ERF) decreased, while the expression of some genes related to antioxidation, osmoregulation, and transcription factors belonging to MYB (Myb proto-oncogene protein) and NAC ((NAM, ATAF1/2, and CUC2) families increased, implying that these genes play key roles in T. chinensis to cope with waterlogging stress. We conclude that T. chinensis is a waterlogging-tolerant species and 10 days of severe waterlogging has induced changes of antioxidant, photosynthesis, and osmoregulation in physiological and transcriptome level. The present study provides candidate genes that can be used for waterlogging-resistant breeding in T. chinensis.