AUTHOR=Peng Ting , Kang Jing-Liang , Xiong Xin-Ting , Cheng Fang-Ting , Zhou Xiao-Juan , Dai Wen-Shan , Wang Min , Li Zhong-Yang , Su Hua-Nan , Zhong Ba-Lian 

TITLE=Integrated Transcriptomics and Metabolomics Analyses Provide Insights Into the Response of Chongyi Wild Mandarin to Candidatus Liberibacter Asiaticus Infection

JOURNAL=Frontiers in Plant Science

VOLUME=Volume 12 - 2021

YEAR=2021

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2021.748209

DOI=10.3389/fpls.2021.748209

ISSN=1664-462X

ABSTRACT=<p><italic>Candidatus</italic> Liberibacter asiaticus (<italic>C</italic>Las) is the causative agent of Huanglongbing (HLB), which has caused great economic losses to the citrus industry. The molecular mechanism of the host response to <italic>C</italic>Las in wild citrus germplasm has been reported less. Eighteen weeks after inoculation <italic>via</italic> grafting, all the <italic>C</italic>Las-inoculated Chongyi wild mandarin (<italic>Citrus reticulata</italic>) were positive and showed severe anatomical aberrations, suggesting its susceptibility to HLB. Transcriptomics and metabolomics analyses of leaves, barks, and roots from mock-inoculated (control) and <italic>C</italic>Las-inoculated seedlings were performed. Comparative transcriptomics identified 3,628, 3,770, and 1,716 differentially expressed genes (DEGs) between <italic>C</italic>Las-infected and healthy tissues in the leaves, barks, and roots, respectively. The <italic>C</italic>Las-infected tissues had higher transcripts per kilobase per million values and more genes that reached their maximal expression, suggesting that HLB might cause an overall increase in transcript accumulation. However, HLB-triggered transcriptional alteration showed tissue specificity. In the <italic>C</italic>Las-infected leaves, many DEGs encoding immune receptors were downregulated. In the <italic>C</italic>Las-infected barks, nearly all the DEGs involved in signaling and plant-pathogen interaction were upregulated. In the <italic>C</italic>Las-infected roots, DEGs encoding enzymes or transporters involved in carotenoid biosynthesis and nitrogen metabolism were downregulated. Metabolomics identified 71, 62, and 50 differentially accumulated metabolites (DAMs) in the <italic>C</italic>Las-infected leaves, barks and roots, respectively. By associating DEGs with DAMs, nitrogen metabolism was the only pathway shared by the three infected tissues and was depressed in the <italic>C</italic>Las-infected roots. In addition, 26 genes were determined as putative markers of <italic>C</italic>Las infection, and a hypothesized model for the HLB susceptibility mechanism in Chongyi was proposed. Our study may shed light on investigating the molecular mechanism of the host response to <italic>C</italic>Las infection in wild citrus germplasm.</p>