Some things get better with age: differences in salicylic acid accumulation and defense signaling in young and mature Arabidopsis

Abstract

In Arabidopsis, much of what we know about the phytohormone salicylic acid (SA) and its role in plant defense comes from experiments using young plants. We are interested in understanding why young plants are susceptible to virulent strains of Pseudomonas syringae, while mature plants exhibit a robust defense response known as age-related resistance (ARR). SA-mediated signaling is important for defense in young plants, however, ARR occurs independently of the defense regulators NPR1 and WHY1. Furthermore, intercellular SA accumulation is an important component of ARR, and intercellular washing fluids from ARR-competent plants exhibit antibacterial activity, suggesting that SA acts as an antimicrobial agent in the intercellular space. Young plants accumulate both intracellular and intercellular SA during PAMP- and effector-triggered immunity, however, virulent P. syringae promotes susceptibility by suppressing SA accumulation using the phytotoxin coronatine. Here we outline the hypothesis that mature, ARR-competent Arabidopsis alleviates coronatine-mediated suppression of SA accumulation. We also explore the role of SA in other mature-plant processes such as flowering and senescence, and discuss their potential impact on ARR.

Stress Marker Signatures in Lesion Mimic Single and Double Mutants Identify a Crucial Leaf Age-Dependent Salicylic Acid Related Defense Signal

“…Also the leaf age-dependent increase in expression of the marker genes in cat2 , and to a lesser extent in dnd1 , were reduced when SA biosynthesis was impaired through the sid2 mutation or the combined sid2 eds1 mutations (Figs 5 and 6). This is consistent with the protective role of SA in age-related resistance to pathogen infection [48]. …”

“…High expression of defense genes in old leaves may be an adaptive response, since older leaves are more resistant to pathogens through e.g. accumulation of SA [48,49]. …”

Tobacco mosaic virus-directed reprogramming of auxin/indole acetic acid protein transcriptional responses enhances virus phloem loading

“…Although no obvious phenotypic differences were observed between pIAA26:: IAA26-P108H-GFP plants and nontransformed control plants, we did find that bolting and the initiation of flowering occurred between week 7 and week 9. This finding is of interest, because previous studies have noted that the development of ARR, defined as the development of resistance in mature tissues, is often associated with transition to flowering (35,78). Within Arabidopsis, ARR has been shown to impact the virulence of P. syringae and the systemic movement of cauliflower mosaic virus (79,80).…”

“…Interestingly, overaccumulation of Aux/IAA proteins in CCs before virus infection led to decreased accumulation and phloem loading of TMV only in mature flowering plants. This correlation with flowering has similarities to age-related resistance (ARR) and suggests that interactions with the identified Aux/IAA proteins may provide TMV with a mechanism to overcome this form of host resistance (35). Based on these studies, we propose that within mature plant tissues TMV selectively targets phloem-expressed Aux/IAA proteins to reprogram functions of the CC-SE complex that contribute to phloem loading.…”

Information Integration and Communication in Plant Growth Regulation

“…Overexpression of HBI1 strongly suppresses the immunity to pathogen and growth inhibition caused by flagellin treatment, supporting a key role for HBI1 in balancing the tradeoff between innate immunity and growth. The aging-induced expression of IBH1 leads to inhibition of HBI1 (Ikeda et al, 2012; Zhang et al, 2009), which is likely to contribute to not only growth arrest but also the enhanced defense response in mature shoots and leaves (Carella et al, 2014; Fan et al, 2014) (Figure 2). …”