An inhibitor of apoptosis (Sf <scp>IAP</scp> ) interacts with <scp>SQUAMOSA</scp> promoter‐binding protein ( <scp>SBP</scp> ) transcription factors that exhibit pro‐cell death characteristics

Abstract

Abstract Despite the importance of proper cell death regulation across broad evolutionary distances, an understanding of the molecular machinery underpinning this fundamental process in plants remains largely elusive. This is despite its critical importance to development, homeostasis, and proper responses to stress. The identification of endogenous plant regulators of cell death has been hindered by the fact that many core regulators of cell death in animals are absent in plant genomes. Remarkably, numerous studies have shown that the ectopic expression of animal prosurvival genes in plants can suppress cell death imposed by many stresses. In this study, we capitalize on the ectopic expression of one of these animal prosurvival genes, an inhibitor of apoptosis from Spodoptera frugiperda ( Sf IAP ), to identify novel cell death regulators in plants. A yeast two‐hybrid assay was conducted using Sf IAP as bait to screen a tomato cDNA library. This screen identified several transcription factors of the SQUAMOSA promoter‐binding protein ( SBP ) family as potential Sf IAP binding partners. We confirmed this interaction in vivo for our top two interactors, Sly SBP 8b and Sly SBP 12a, using coimmunoprecipitation. Interestingly, overexpression of Sly SBP 8b and Sly SBP 12a induced cell death in Nicotiana benthamiana leaves. Overexpression of these two transcription factors also induced the accumulation of reactive oxygen species and enhanced the growth of the necrotrophic pathogen Alternaria alternata . Fluorescence microscopy confirmed the nuclear localization of both Sly SBP 8b and Sly SBP 12a , while Sly SBP 12a was also localized to the ER membrane. These results suggest a prodeath role for Sly SBP 8b and Sly SBP 12a and implicate ER membrane tethering as a means of regulating Sly SBP 12a activity.