The Arabidopsis N-terminal Acetyltransferase NAA50 Regulates Plant Growth and Defense

Abstract

Stress signaling in plants is carefully regulated to ensure proper development and reproductive fitness. Overactive defense signaling can result in dwarfism as well as developmental defects. In addition to requiring a significant amount of energy, plant stress responses place a burden upon the cellular machinery, which can result in the accumulation of misfolded proteins and endoplasmic reticulum (ER) stress. Negative regulators of stress signaling, such as EDR1, ensure that stress responses are properly suspended when they are not needed. Here, we describe the role of an uncharacterized N-terminal acetyltransferase, NAA50, in the regulation of plant development and stress responses. Our results demonstrate that NAA50, an interactor of EDR1, plays an important role in regulating the tradeoff between plant growth and defense. Plants lacking NAA50 display severe developmental defects as well as induced stress responses. Reduction of NAA50 expression results in arrested stem and root growth and senescence. Furthermore, our results demonstrate that EDR1 and NAA50 are required for suppression of ER stress signaling. This work establishes that NAA50 is essential for plant development and the suppression of stress responses, likely through the regulation of ER stress. These experiments demonstrate a role for N-terminal acetylation in the suppression of ER stress, as well as the tradeoff between stress responses and development.One Sentence SummaryKnockout in Arabidopsis of the broadly conserved N-terminal acetyl transferase NAA50 induces ER stress, leading to severe dwarfism and induction of defense responses.

NAA50 Is an Enzymatically Active Nα-Acetyltransferase That Is Crucial for Development and Regulation of Stress Responses

“…Salicylic acid is also an important positive regulator of the plant immune response. In agreement with this finding, an increase in the expression of defense genes and salicylic acid signaling is observed in naa50 mutants (Neubauer and Innes, 2020). We find this transcriptional increase reflected at the protein level (2.1-fold up-regulation of proteins involved in the defense response).…”

“…4, A and B), we cannot exclude a role of nucleus-localized NAA50 in the constitutive induction of stress responses in naa50 mutants. The multiple localization of AtNAA50-EYFP in the cytosol and the ER has been independently confirmed by Neubauer and Innes (2020). The authors want to put a note of caution on the nuclear localization of AtNAA50-EYFP, since EYFP on its own is known to display nucleocytoplasmic localization (Chen et al, 2020).…”

“…Until now, it was unclear whether NAA50 associates with the core NatA complex in plants. However, the colocalization of NAA10 and NAA50 was evidenced in the cytoplasm (Neubauer and Innes, 2020). Although ScNAA50 is inactive, it positively impacts NatA activity by modulating the enzymatic activity of ScNAA10 (Deng et al, 2019) and by positioning the NatA complex in close proximity to the ribosomal tunnel exit (Knorr et al, 2019).…”

“…in the Arabidopsis genome (Bienvenut et al, 2012;Neubauer and Innes, 2020). However, the enzymatic activity and substrate specificity of this putative plant NatE have not been characterized yet.…”

“…We find that among the proteins accumulating in naa50-2 mutants, proteins involved in the ER stress response are 3.4-fold overrepresented. The accumulation of ER stress-associated proteins can be explained by an enhanced transcription of these genes due to increased splicing of the transcription factor bZIP60 observed in naa50-1 seedlings (Neubauer and Innes, 2020). Unspliced bZIP60 resides in the ER membrane due to a C-terminal transmembrane domain.…”