Transcriptome analysis of lily exhibiting enhanced resistance against gray mold triggered by Bacillus cereus C1L

This research is to analysis the influence of Bacillus cereus C1L on what hormone signaling sectors to regulates defense response of Botrytis elliptica-infected lily by next-generation sequencing (NGS) and microarray analyses. The result may help to identify the regulation of monocot defense related hormone signaling pathway triggered by rhizobacteria and promotes the understanding of resistance physiology of monocot. Total RNAs were collected from B. cereus C1L-drenched leaves, B. elliptica-inoculated leaves, B. elliptica-inoculated leaves pre-drenched with B. cereus C1L and untreated control of lily plants for NGS analysis. Among 78,674contigs, 35% of contigs hit the reference sequences. To identify unique gene differentially expressed while triggered by B. cereus C1L on B. elliptica-inoculated lily, a criteria of variety over 0.5 of each treatment was set for selecting those contigs with expression pattern similar between NGS and customized array to create venn diagram. In this venn diagram analysis, expression of 383 contigs exhibited up-regulation while 113 contigs were down-regulated. Their functions related to plant defenses involved abscisic acid (ABA) signaling, stomatal closure regulation, hydrogen peroxide response and glutathione S-transferase, indicating that ABA signaling may play a role in lily systemic resistance against B. elliptica as triggered by B. cereus C1L. To further study about which hormone signaling pathway B. cereus C1L may utilize to strengthen resistance of lily against B. elliptica, the most similar contig homologs to the selected key gene sequences in different defense signaling pathway of Arabidopsis were selected for the analysis of heat map. Results showed that B. cereus C1L probably increase lily resistance through jasmonic acid (JA), ethylene (ET) and ABA signaling pathway. Quantitative real-time polymerase chain reaction analysis verified that pre-drench with B. cereus C1L could activate JA signaling sector upon B. elliptica attack. Besides, ABA treatment could increase stomatal closure rate and reduce the infection by B. elliptica, indicating an involvement of ABA signaling in C1L-conducted defense response. In the leaf disc assay, treatments with JA, ET or ABA at the same time of B. elliptica inoculation decreased symptom development; however, treatment with salicylic acid did not show significant effect on symptom development. These results collectively suggested that activations of JA/ET and ABA signaling sectors had positive contribution to the defense against B. elliptica. As a whole, according to results of venn diagram, heat map, leaf disc test and stomatal closure rate, B. cereus C1L–induced systemic resistance against B. elliptica in lily regulated by JA/ET and ABA signaling sectors was presumed.