75 Integrating Membrane Transport with Male Gametophyte ... - TAIR

281 Arabidopsis thaliana Defense Response Triggered by Brevicoryne brassicae Attack Has
Different Intensity in Ecotypes with Diverse Glucosinolate Profiles
Anna Kusnierczyk 1 , Per Winge 1 , Herman Midelfart 1 , John Rossiter 2 , Scott Armbruster 1 , Atle Bones 1
1
Department of Biology, The Norwegian University of Science and Technology, Realfagbygget, 7491Trondheim,
NO, 2 Department of Biology, Imperial College at Wye, University of London, Wye, Kent TN25 5AH, UK
Phloem piercing-sucking insects are an important factor that limits crop plants production. Aphids, despite sophisticated
feeding strategy minimizing cell damage, activate responses broadly similar to those triggered by pathogen attack,
chewing herbivore and wounding. Defense strategies of most plants involve signaling molecules such as jasmonic
acid (JA), salicylic acid (SA) and ethylene (ET), along with glucosinolates and their hydrolysis products in cruciferous
species. Pests which specialized to feed on Brassicaceae have evolved various mechanisms to protect themselves
against toxic products of glucosinolate hydrolysis. Cabbage aphid, Brevicoryne brassicae, produces an enzyme similar
to plant myrosinase, which is able to hydrolyze plant glucosinolates. We used oligonucleotide microarrays to study the
changes in transcriptional profile of plants infested with B. brassicae. Three Arabidopsis thaliana ecotypes differing
in predominant products of glucosinolate hydrolysis were chosen: Wassilewskija (Ws), Cape Verde Islands (Cvi), and
Landsberg erecta (Ler), which produce mainly isothiocyanates, epithionitriles and nitriles, respectively. In all three
ecotypes, the major pathways involved in plant defense were up-regulated upon aphid attack, but the expression level
of genes involved in these pathways varied. The JA synthesis pathway was induced highest in Cvi, while the indolic
glucosinolate synthesis pathway was strongest up-regulated in Ler. In contrast, two genes coding for plant myrosinases:
thioglucoside glucohydrolase 1 and 2 (TGG1 and TGG2) were down-regulated.
282 Salicylic Acid-Mediated Innate Immunity in Arabidopsis is Regulated by SIZ1 SUMO E3
ligase
Jiyoung Lee 1 , Jaesung Nam 2 , Kenji Miura 3 , Jingbo Jin 3 , Chan Yul Yoo 3 , Paul M. Hasegawa 3 , Dae-Jin Yun 1
1
Gyeongsang National University, 2 DongA University, Pusan, South of Korea, 3 Purdue University, IN, USA
Reversible post-translational modification of proteins by small ubiquitin-related modifier (SUMO) protein is involved
in many important cellular processes in yeasts and animals. However, little is known about the function of sumoylation
in plants. In this study, we show that the SIZ1 gene encoding an Arabidopsis SUMO E3 ligase regulates innate immunity.
siz1 plants exhibit constitutive systemic acquired resistance (SAR) that is characterized by elevated accumulation of
salicylic acid (SA), increased resistance to the bacterial pathogen Pseudomonas syringae pv. tomato (Pst) DC3000 and
constitutive pathogenesis-related (PR) gene expression. In siz1 plants expressing SA hydroxylase nahG (siz1-2 nahG),
disease resistance is linked to elevated SA levels. In addition, levels of PAD4, EDS1, EDS5 and SID2 transcripts were
induced strongly, whereas expression of NDR1 or NPR1 was similar to wild-type. The effect of siz1 on SA signaling
was studied using the double mutants siz1npr1, siz1pad4 and siz1ndr1. SIZ1 and PAD4 interact epistatically to regulate
PR expression and disease resistance. Consistent with these observations, siz1 plants exhibited enhanced resistance to
Pst DC3000 expressing avrRps4, a bacterial avirulence determinant that responds to the EDS1/PAD4-dependent TIR-
NBS type R gene. In contrast, siz1 plants did not demonstrate resistance to Pst DC3000 expressing avrRpm1, a bacterial
avirulence determinant that responds to the NDR1-dependent CC-NBS type R gene. Jasmonic acid (JA)-induced PDF1.2
expression and susceptibility to Botrytis cinerea were unaltered in siz1 plants. Taken together, our results suggest that
SIZ1 regulates PAD4-mediated SA signaling, which in turn confers innate immunity in Arabidopsis.