Download AtSR1 gene plays dual roles in plant defense

AtSR1 gene plays dual roles in plant defense/immunity
Peiguo Yuan, Ph.D. student
Department of Horticulture
Washington State University
Facing pathogen attack, plant cells need to make a life or death decision to respond to pathogen
infection. Two types of immune reactions are commonly observed in plant disease resistance responses,
basal resistance (BR) and hypersensitive response (HR). Basal resistance can be triggered by recognition
of microbe-associated molecular patterns (MAMPs), such as flagellin, and this is the first line of inducible
plant resistance that protects plants against most types of pathogens. The result is that plants become
fortified against pathogen attack. However, basal resistance can be suppressed by pathogen-encoded
effectors which act to suppress plant immunity. In turn, plants could gain the ability to recognize the
pathogen-encoded effectors and trigger stronger defense with a hallmark of the hypersensitive
response. HR is characterized by deliberate programmed cell death (PCD) at the site of infection. By
sacrificing local cells, pathogen growth is limited due to lack of water and nutrients, and the rest of the
plant can survive the attack.
Arabidopsis thaliana Signal Responsive 1 (AtSR1), also known as Calmodulin-binding Transcription
Activator3 (CAMTA3), encodes a transcription factor regulated by Ca2+/calmodulin (CaM). Previous
studies revealed that a loss-of-function mutation of AtSR1 resulted in elevated defense against a virulent
strain of Pst DC3000 bacteria (elevated basal resistance). Further investigations have revealed that
AtSR1 contributed to plant defense by binding to the “vCGCGb” box in the promoter of its target gene
EDS1 (Enhanced Disease Susceptibility1) and suppressed its expression and subsequent activation of
salicylic acid-mediated plant immunity. Therefore, AtSR1 plays a negative role in the regulation of
resistance. However, we recently found that HR is compromised in atsr1. When infiltrated with an
avirulent strain of Pst DC3000 (Pst DC 3000 avrRpt2), HR could be observed in wild-type (WT) plants but
not in atsr1 mutant plants. Disease resistance test showed that growth of Pst DC3000 carrying avrRpt2
is significantly increased in atsr1 than in WT plants. Furthermore, in WT plants the transcription of
AtSR1 was not affected during basal resistance (BR), but was significantly induced during HR. Hence,
this induced expression of AtSR1 could favor the establishment of HR. These results document that
AtSR1 plays dual roles in plant defense/immunity. Furthermore, these results also show that AtSR1 is a
suppressor of BR and an activator of HR.