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Article|01 Jun 2020|OPEN
The integration of transcriptomic and transgenic analyses reveals the involvement of the SA response pathway in the defense of chrysanthemum against the necrotrophic fungus Alternaria sp.
Xiting Zhao1,2, Lingyu Song1, Liwei Jiang1, Yuting Zhu1, Qinghui Gao3, Dandan Wang1, Jing Xie1, Meng Lv1, Ping Liu1 & Mingjun Li1,2
1College of Life Sciences, Henan Normal University, Xinxiang 453007, China
2Engineering Technology Research Center of Nursing and Utilization of Genuine Chinese Crude Drugs in Henan Province, Xinxiang 453007, China
3College of Mathematics and Information Science, Henan Normal University, Xinxiang 453007, China

Horticulture Research 7,
Article number: 80 (2020)
doi: 10.1038/hortres.2020.80
Views: 517

Received: 06 Aug 2019
Revised: 11 Mar 2020
Accepted: 20 Mar 2020
Published online: 01 Jun 2020

Abstract

Chrysanthemum morifolium cv. ‘Huaihuang’ has ornamental, edible, medicinal, and tea product uses. However, its field growth, yield, and quality are negatively affected by black spot disease caused by Alternaria sp. (Strain: HQJH10092301; GenBank accession number: KF688111). In this study, we transcriptionally and transgenically characterized a new cultivar, ‘Huaiju 2#’ (Henan Traditional Chinese Medicine Plant Cultivar identification number: 2016002), which was bred from ‘Huaihuang’ and shows resistance to Alternaria sp. Numerous ‘Huaiju 2#’ plants were inoculated with Alternaria sp. for three or five days. Metabolic analysis showed increases in both salicylic acid (SA) and jasmonic acid (JA) in infected plants compared to the control. Protein activity analysis also revealed a significant increase in defense enzyme activities in infected plants. RNA-Seq of plants infected for 3 or 5 days produced a total of 58.6 GB of clean reads. Among these reads, 16,550 and 13,559 differentially expressed genes (DEGs) were identified in Cm_3 dpi (sample from 3 days post-inoculation labeled as Cm_3 dpi) and Cm_5 dpi (sample from 5 days post-inoculation labeled as Cm_5 dpi), respectively, compared with their controls (Cm_0 d: a mixture samples from 0 d (before inoculation) and those treated with sterile distilled water at 3 dpi and 5 dpi). Gene annotation and cluster analysis of the DEGs revealed a variety of defense responses to Alternaria sp. infection, which were characterized by increases in resistance (R) proteins and the reactive oxygen species (ROS), Ca2+, mitogen-activated protein kinase (MAPK), and JA signaling pathways. In particular, SA signaling was highly responsive to Alternaria sp. infection. The qPCR analysis of 12 DEG candidates supported their differential expression characterized by using the RNA-Seq data. One candidate was CmNPR1 (nonexpressor of pathogenesis-related gene 1), an important positive regulator of SA in systemic acquired resistance (SAR). Overexpression of CmNPR1 in ‘Huaiju 2#’ increased the resistance of transgenic plants to black spot. These findings indicate that the SA response pathway is likely involved in the defense of ‘Huaiju 2#’ against Alternaria sp. pathogens.