ABA Regulation of Plant Response to Biotic Stresses - Abscisic Acid: Metabolism, Transport and Signaling - page 410

be generalized to one particular pathogen lifestyle (biotroph, hemibiotroph, or necro-
troph), and the exact role that conferred by ABA may correlate with the specific vir-
ulence strategies adopted by individual pathogen species. In turn, since the cross talk
between ABA and SA or JA/ET may be bidirectional, and indeed, accumulated stud-
ies have demonstrated that the SA and JA/ET are also involved in various plant abi-
otic stresses (Miura and Tada 2014 ; Fujita et al. 2006 ; Ballar￩ et al. 2011 ), it would
be reasonable to deduce that biotic stresses may also affect the response of plants to
abiotic stresses (Yasuda et al. 2008 ; Mosher et al. 2010 ; Moeder et al. 2010 ). Thus,
ABA functions as a crucial regulator during the adaption of plant to the variable
environment by mediating the cross talk between biotic and abiotic stresses.
Furthermore, besides of the ABA pathway core components, more and more
proteins, such as various transcription factors (such as WRKYs, MYBs, NACs)
and histone deacetylases, were all demonstrated to be involved in both ABA sign-
aling and biotic stresses (Rushton et al. 2010 ; Chen et al. 2012 ; Seo and Park
2010 ; Jensen et al. 2008 ; Chen and Wu 2010 ; Kim et al. 2008 ); thus, these proteins
may also participate in the cross talk between biotic and abiotic stresses through
the coordination with the ABA pathway core components. Further molecular
studies of such proteins will add new insights into the ABA-regulated cross talk
between biotic and abiotic stress responses.
20.14 Conclusions and Perspective
As presented in this chapter, the abiotic hormone ABA has been emerged as an criti-
cal regulator in plant biotic stresses. Compared with the positive roles of ABA in sto-
mata innate immunity, it has both positive and negative effects on callose deposition
and ROS generation which may be determined by the time and location of infection
or the combination of host plant and attackers. Generally, ABA functions in plant
biotic stresses by cross talk antagonistically or synergistically with the SA-JA-ET
backbone of the plant immune signaling network. However, the underlying mecha-
nisms that control the cross talk remained largely unknown. We supposed that the
cross talk may be conducted through direct interactions of one hormone pathway's
core component with another pathway's core component or direct binding of a given
DNA binding protein in one hormone pathway to its target gene that functions in
another pathway. Future research on this fine-tuning of signaling pathways will add
our knowledge to better understand the complex cross talk between ABA and SA-
JA-ET-mediated stress responses. Furthermore, since there exists an evident trade-
off between abiotic stress tolerance and biotic defense, we should consider more
when attempting to manipulate the ABA signaling for modern agriculture.
Acknowledgments The work in the authors' laboratory was supported by the Natural Science
Foundation of China (31200915), the West Light Foundation of CAS, and Yong Innovation
Promotion Association of the Chinese Academy of Sciences. We apologize to the colleagues
whose work could not be cited here because of space restrictions.