Abstract:
The NONEXPRESSOR OF PATHOGENESIS-RELATED GENES 1 (NPR1) and related
NPR1-like proteins are a functionally similar, yet surprisingly diverse family of
transcription co-factors. Initially, NPR1 in Arabidopsis was identified as a positive
regulator of systemic acquired resistance (SAR), paralogs NPR3 and NPR4 were later
shown to be negative SAR regulators. The mechanisms involved have been the subject
of extensive research and debate over the years, during which time a lot has been
uncovered. The known roles of this protein family have extended to include influences
over a broad range of systems including circadian rhythm, endoplasmic reticulum (ER)
resident proteins and the development of lateral organs. Recently, important advances
have been made in understanding the regulatory relationship between members of the
NPR1-like protein family, providing new insight regarding their interactions, both with
each other and other defense-related proteins. Most importantly the influence of salicylic
acid (SA) on these interactions has become clearer with NPR1, NPR3, and NPR4
being considered bone fide SA receptors. Additionally, post-translational modification
of NPR1 has garnered attention during the past years, adding to the growing regulatory
complexity of this protein. Furthermore, growing interest in NPR1 overexpressing crops
has provided new insights regarding the role of NPR1 in both biotic and abiotic stresses
in several plant species. Given the wealth of information, this review aims to highlight and
consolidate the most relevant and influential research in the field to date. In so doing,
we attempt to provide insight into the mechanisms and interactions which underly the
roles of the NPR1-like proteins in plant disease responses.
