The Involvement of Jasmonic Acid, Ethylene, and Salicylic Acid in the Signaling Pathway of Clonostachys rosea-Induced Resistance to Gray Mold Disease in Tomato.

Tomato gray mold disease caused by Botrytis cinerea is a serious disease that threatens tomato production around the world. Clonostachys rosea has been used successfully as a biocontrol agent against divergent plant pathogens, including B. cinerea. To understand the signal transduction pathway of C. rosea-induced resistance to tomato gray mold disease, the effects of C. rosea on gray mold tomato leaves along with changes in the activities of three defense enzymes (phenylalanine ammonialyase [PAL], polyphenol oxidase [PPO], and catalase [CAT]), second messengers (nitric oxide [NO], hydrogen peroxide [H2O2], and superoxide anion radical [O2-]), and stress-related genes (mitogen-activated protein kinase [MAPK], WRKY, Lexyl2, and atpA) in four different hormone-deficient (jasmonic acid [JA], ethylene [ET], salicylic acid [SA], and gibberellin) tomato mutants were investigated. The results revealed that C. rosea significantly inhibited the growth of mycelia and spore germination of B. cinerea. Furthermore, it reduced the incidence of gray mold disease, induced higher levels of PAL and PPO, and induced lower levels of CAT activities in tomato leaves. Moreover, it also increased NO, H2O2, and O2- levels and the gene expression levels of WRKY, MAPK, atpA, and Lexyl2. The incidence of gray mold disease in four hormone-deficient mutants was higher than that in the corresponding wild-type tomato plants. Among all of these hormone-deficient tomato mutants, JA had the most significant effect in regulating the different signal molecules. Additional study suggested that JA upregulated the expression of Lexyl2, MAPK, and WRKY but downregulated atpA. Furthermore, JA also enhanced the activity of PAL, PPO, and CAT and the production of NO and H2O2. SA downregulated CAT and PAL, whereas ET upregulated PAL but downregulated CAT. This study is of significance in understanding the regulatory pathways and biocontrol mechanism of C. rosea against B. cinerea.

Effects of low temperature on mRNA and small RNA transcriptomes in Solanum lycopersicoides leaf revealed by RNA-Seq.

The plant low temperature tolerance mechanisms have been studied in the Arabidopsis, tomato, Solanum commersonii, Solanum tuberosum, Chorispora bungeana, and Chinese cabbage at the transcriptional level. Some genome-wide works to identify cold-regulated genes, but no comprehensive research of the Solanum lycopersicoides transcriptome under low temperature stress have been performed. S. lycopersicoides is more freeze-tolerant than the cultivated tomato. We analyzed the low temperature transcriptomes and small RNA fractions of S. lycopersicoides leaf tissue using an Illumina platform for high-throughput RNA sequencing (RNA-seq). There were 59,286 unigenes obtained using de novo assembly, and 2052 down-regulated and 2409 up-regulated unigenes were identified in response to chilling. The expression of six cold-regulated genes was confirmed by qPCR. Some biological processes were showed, by gene ontology term enrichment analysis of the cold-regulated genes, including 'response to stimulus', 'signaling', and 'cell killing' in the response of S. lycopersicoides to chilling. In addition, we identified a total of 952 novel miRNA candidates that may regulate relevant target genes. Our data indicated that certain miRNAs (e.g., sly-miR156a, sly-miR397, and unconservative_SL2.50ch00_21686) play roles in response to low temperature stress. Sequencing of mRNAs and miRNAs revealed new genes and allowed us to have new assumptions for a low temperature tolerance mechanism.

Transcriptome Analysis of the Cf-12-Mediated Resistance Response to Cladosporium fulvum in Tomato.

Cf-12 is an effective gene for resisting tomato leaf mold disease caused by Cladosporium fulvum (C. fulvum). Unlike many other Cf genes such as Cf-2, Cf-4, Cf-5, and Cf-9, no physiological races of C. fulvum that are virulent to Cf-12 carrying plant lines have been identified. In order to better understand the molecular mechanism of Cf-12 gene resistance response, RNA-Seq was used to analyze the transcriptome changes at three different stages of C. fulvum infection (0, 4, and 8 days post infection [dpi]). A total of 9100 differentially expressed genes (DEGs) between 4 and 0 dpi, 8643 DEGs between 8 and 0 dpi and 2547 DEGs between 8 and 4 dpi were identified. In addition, we found that 736 DEGs shared among the above three groups, suggesting the presence of a common core of DEGs in response to C. fulvum infection. These DEGs were significantly enriched in defense-signaling pathways such as the calcium dependent protein kinases pathway and the jasmonic acid signaling pathway. Additionally, we found that many transcription factor genes were among the DEGs, indicating that transcription factors play an important role in C. fulvum defense response. Our study provides new insight on the molecular mechanism of Cf resistance to C. fulvum, especially the unique features of Cf-12 in responding to C. fulvum infection.