Abstract
Proteins with conserved SET domain play a critical role in plant immunity. However, the means of organization and functions of these proteins are unclear, particularly in non-model plants such as pepper (
Capsicum annum
L.). Herein, we functionally characterized
CaASHH3
, a member of class II (the ASH1 homologs H3K36) proteins in pepper immunity against
Ralstonia solanacearum
and
Pseudomonas syringae
pv
tomato
DC3000 (
Pst
DC3000). The
CaASHH3
was localized in the nucleus, and its transcript levels were significantly enhanced by
R. solanacearum
inoculation (RSI) and exogenous application of salicylic acid (SA), methyl jasmonate (MeJA), ethephon (ETH), and abscisic acid (ABA). Knockdown of
CaASHH3
by virus-induced gene silencing (VIGS) compromised peppers’ resistance to RSI. Furthermore, silencing of
CaASHH3
impaired hypersensitive-response (HR)-like cell death response due to RSI and downregulated defense-associated marker genes, including
CaPR1
,
CaNPR1
, and
CaABR1.
The
CaASHH3
protein was revealed to affect the promoters of
CaNPR1
,
CaPR1
, and
CaHSP24.
Transiently over-expression of
CaASHH3
in pepper leaves elicited HR-like cell death and upregulated immunity-related marker genes. To further study the role of
CaASHH3
in plant defense in vivo,
CaASHH3
transgenic plants were generated in
Arabidopsis
. Overexpression of
CaASHH3
in transgenic
Arabidopsis thaliana
enhanced innate immunity against
Pst
DC3000. Furthermore,
CaASHH3
over-expressing transgenic
A. thaliana
plants exhibited upregulated transcriptional levels of immunity-associated marker genes, such as
AtNPR1
,
AtPR1
, and
AtPR2
. These results collectively confirm the role of
CaASHH3
as a positive regulator of plant cell death and pepper immunity against bacterial pathogens, which is regulated by signaling synergistically mediated by SA, JA, ET, and ABA.