Tomato histone H2B monoubiquitination enzymes SlHUB1 and SlHUB2 contribute to disease resistance against Botrytis cinerea through modulating the balance between SA- and JA/ET-mediated signaling pathways.
BACKGROUND
Histone H2B monoubiquitination pathway has been shown to play critical roles in regulating growth/development and stress response in Arabidopsis. In the present study, we explored the involvement of the tomato histone H2B monoubiquitination pathway in defense response against Botrytis cinerea by functional analysis of SlHUB1 and SlHUB2, orthologues of the Arabidopsis AtHUB1/AtHUB2.


METHODS
We used the TRV-based gene silencing system to knockdown the expression levels of SlHUB1 or SlHUB2 in tomato plants and compared the phenotype between the silenced and the control plants after infection with B. cinerea and Pseudomonas syringae pv. tomato (Pst) DC3000. Biochemical and interaction properties of proteins were examined using in vitro histone monoubiquitination and yeast two-hybrid assays, respectively. The transcript levels of genes were analyzed by quantitative real time PCR (qRT-PCR).


RESULTS
The tomato SlHUB1 and SlHUB2 had H2B monoubiquitination E3 ligases activity in vitro and expression of SlHUB1 and SlHUB2 was induced by infection of B. cinerea and Pst DC3000 and by treatment with salicylic acid (SA) and 1-amino cyclopropane-1-carboxylic acid (ACC). Silencing of either SlHUB1 or SlHUB2 in tomato plants showed increased susceptibility to B. cinerea, whereas silencing of SlHUB1 resulted in increased resistance against Pst DC3000. SlMED21, a Mediator complex subunit, interacted with SlHUB1 but silencing of SlMED21 did not affect the disease resistance to B. cinerea and Pst DC3000. The SlHUB1- and SlHUB2-silenced plants had thinner cell wall but increased accumulation of reactive oxygen species (ROS), increased callose deposition and exhibited altered expression of the genes involved in phenylpropanoid pathway and in ROS generation and scavenging system. Expression of genes in the SA-mediated signaling pathway was significantly upregulated, whereas expression of genes in the jasmonic acid (JA)/ethylene (ET)-mediated signaling pathway were markedly decreased in SlHUB1- and SlHUB2-silenced plants after infection of B. cinerea.


CONCLUSIONS
VIGS-based functional analyses demonstrate that both SlHUB1 and SlHUB2 contribute to resistance against B. cinerea most likely through modulating the balance between the SA- and JA/ET-mediated signaling pathways.
National Key Laboratory for Rice Biology, Institute of Biotechnology, Zhejiang University, Hangzhou, 310058, China. zyfzjhzyh@163.com.
Yafen
Y
Zhang
National Key Laboratory for Rice Biology, Institute of Biotechnology, Zhejiang University, Hangzhou, 310058, China. dyli@zju.edu.cn.
Dayong
D
Li
National Key Laboratory for Rice Biology, Institute of Biotechnology, Zhejiang University, Hangzhou, 310058, China. zhanghj82@zju.edu.cn.
Huijuan
H
Zhang
National Key Laboratory for Rice Biology, Institute of Biotechnology, Zhejiang University, Hangzhou, 310058, China. yongbohong@126.com.
Yongbo
Y
Hong
National Key Laboratory for Rice Biology, Institute of Biotechnology, Zhejiang University, Hangzhou, 310058, China. leihero2008@163.com.
Lei
L
Huang
National Key Laboratory for Rice Biology, Institute of Biotechnology, Zhejiang University, Hangzhou, 310058, China. 1058772250@qq.com.
Shixia
S
Liu
National Key Laboratory for Rice Biology, Institute of Biotechnology, Zhejiang University, Hangzhou, 310058, China. 445497742@qq.com.
Xiaohui
X
Li
National Key Laboratory for Rice Biology, Institute of Biotechnology, Zhejiang University, Hangzhou, 310058, China. oyfry@163.com.
Zhigang
Z
Ouyang
National Key Laboratory for Rice Biology, Institute of Biotechnology, Zhejiang University, Hangzhou, 310058, China. fmsong@zju.edu.cn.
Fengming
F
Song
D000595:Amino Acid Sequence; D020171:Botrytis / Q000502:physiology*; D002473:Cell Wall / Q000378:metabolism; D003517:Cyclopentanes / Q000378:metabolism; D060467:Disease Resistance; D005030:Ethylenes / Q000378:metabolism; D018506:Gene Expression Regulation, Plant; D020868:Gene Silencing / Q000187:drug effects; D006657:Histones / Q000378:metabolism*; D018551:Solanum lycopersicum / Q000201:enzymology* / Q000235:genetics; D008969:Molecular Sequence Data; D054883:Oxylipins / Q000378:metabolism; D010935:Plant Diseases / Q000235:genetics / Q000382:microbiology; D010937:Plant Growth Regulators / Q000494:pharmacology; D010940:Plant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D020005:Propanols / Q000378:metabolism; D011485:Protein Binding / Q000187:drug effects; D017382:Reactive Oxygen Species / Q000378:metabolism; D020156:Salicylic Acid / Q000378:metabolism; D015398:Signal Transduction; D044767:Ubiquitin-Protein Ligases / Q000378:metabolism; D054875:Ubiquitination
D003517:Cyclopentanes; D005030:Ethylenes; D006657:Histones; D054883:Oxylipins; D010937:Plant Growth Regulators; D010940:Plant Proteins; D020005:Propanols; D017382:Reactive Oxygen Species; C439395:1-phenylpropanol; C011006:jasmonic acid; C036216:ethylene; D044767:Ubiquitin-Protein Ligases; D020156:Salicylic Acid