3.5 Involvement of on OsMYC2 in Pi starvation-enhanced JA
signaling and Xoo resistance
To further discern whether OsMYC2 is involved in Pi
starvation-induced Xoo resistance, we generated OsMYC2mutants using the CRISPR/Cas9 system. Two homozygous lines
(myc2-3 and myc2-6 ) were obtained and confirmed by
sequencing (Figure S2a). To investigate JA sensitivity, theOsMYC2 CRISPR/Cas9 mutants and NIP plants were grown with added
MeJA. As expected, the transgenic lines displayed less sensitivity to
MeJA than the WT plants (Figure S2b and c), indicating OsMYC2 is
required for JA signaling in rice.
To investigate the role of OsMYC2 in Pi starvation signaling, we
first measured the expression ofOsMYC2 -mediated
JA response genes in myc2 plants upon Pi starvation. As shown in
Figure 6(a), JA-responsive genes were significantly more highly
expressed in Pi-starved NIP plants than in the Pi-sufficient control. Inmyc2-3 and myc2-6 plants, however, Pi deficit suppressed
these Pi starvation-inducible JA-responsive genes, except forOsMYC2 itself (Figure 6a). Phytohormone measurement revealed that
the production of MeJA in response to Pi starvation was abolished inmyc2 mutants (Figure 6b). JA-IIe content was lower in myc2mutants compared with NIP control, and the level of JA-IIe was not
changed upon Pi starvation in both myc2 and NIP plants (Figure
S1c). We also performed Xoo resistance tests on these transgenic
lines grown under
Pi
sufficiency or starvation.
9-15
days after inoculated with Xoo , we measured bacterial
proliferation of plants grown in the normal condition. The results
showed that the sensitivity to Xoo in myc2-3 andmyc2-6 plants was higher than that of in NIP controls (Figure
6c). However,
Pi
starvation-treated myc2-3 and myc2-6 plants showed
proliferation comparable to that in the control, whereas proliferation
in Pi starvation-treated wild-type NIP plants was significantly reduced
(Figure 6c). Blight lesion length displayed similar patterns as observed
for bacterial population in myc2-3 and myc2-6 plants
compared with NIP controls under both Pi-sufficient and -deficient
conditions (Figure 6d and e), indicating a role for OsMYC2 in the
Pi starvation-enhanced defense response. Thus, our results suggest thatOsMYC2 is necessary for Pi starvation-induced enhancement of the
JA signaling and defense response.