Transcriptome Analysis Reveals Defense Responses of Alfalfa Seedling Roots to Sclerotium rolfsii

世朕 贾 ¹ Zhencuo Dan ¹ He Li ² Yuhan Guo ¹ Lei Jia ¹ Ailing Yu ¹ Huitong Zhan ¹ Xiangjun Liu ¹ Teng Gao ¹ Yun Shi ¹ Zeng-Yu Wang ^1* Lili Cong ^1*

• ¹ Qingdao Agricultural University, Qingdao, China
• ² Hinggan League Academy of Agriculture and Animal Husbandry, Ulanhot, Mongolia

Sclerotium rolfsii was identified as the primary pathogen causing plant damage. In this study, the isolated and identified S. rolfsii strain CZL1 was confirmed as the main pathogen responsible for the root rot outbreak in experimental fields in Qingdao, Shandong Province. Additionally, this pathogen can also cause root diseases in alfalfa relatives, such as Medicago truncatula, soybean (Glycine max), and mung bean (Vigna radiata). To explore the interaction mechanisms between alfalfa and the pathogen and identify key regulatory factors involved in disease resistance, this study utilized M. sativa cv. WuDi as the experimental material. Following inoculation with strain CZL1, root samples were collected at 24 hours post-inoculation (hpi) and 4 days post-inoculation (dpi) for transcriptome sequencing. 11,433 and 12,063 DEGs were identified at CK (Control, non-inoculated) versus T24 h (24 hpi) and CK versus T4 d (4 dpi), respectively. Plant hormone signal transduction had the highest number of DEGs at 24 hpi, while plant-pathogen interaction pathways dominated at 4 dpi. Enrich analyses further validated the crucial roles of plant hormone signal transduction and plant-pathogen interaction pathways in the disease resistance mechanisms of alfalfa. The three identified top terms contained key genes belonging to multiple protein families, including PR-1 (Pathogenesis-Related protein 1), PPR (Pentatricopeptide Repeat protein), F-box (F-box Kelch-repeat protein) with PR-1 being the most enriched. In the phenylpropanoid biosynthesis pathway, lignin and flavonoids play crucial roles in disease resistance. Key genes involved in their synthesis, such as PAL, C4H, 4CL, CHS, and CHI, are particularly important. Subsequently, the analysis identified the 20 most abundant transcription factor families, among which the WRKY transcription factors (TFs) is involved in regulating multiple key metabolic pathways. These results clarify the involvement of key factors in alfalfa after the inoculation of S. rolfsii, providing a theoretical basis for future research on disease resistance in alfalfa.