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Abstract: Seven in absentia (SINA) protein is one subgroup of ubiquitin ligases possessing an N‐terminal cysteine‐rich really interesting new gene (RING) domain, two zinc‐finger motifs, and a C‐terminal domain responsible for substrate‐binding and dimerization. In tomato (Solanum lycopersicum), the SINA gene family has six members, and we characterize in this study all tomato SINA (SlSINA) genes and the gene products. Our results show that SlSINA genes are differentially regulated in leaf, bud, stem, flower, and root. All SlSINA proteins possess RING‐dependent E3 ubiquitin ligase activity, exhibiting similar specificity towards the E2 ubiquitin‐conjugating enzyme. SlSINA1/3/4/5/6 are localized in both cytoplasm and nucleus, whereas SlSINA2 is exclusively localized in the nucleus. Moreover, all SlSINAs can interact with each other for homo‐ or hetero‐dimerization. The functionality of SlSINA proteins has been investigated. SlSINA4 plays a positive role in defense signalling, as manifested by elicitation of E3‐dependent hypersensitive response‐like cell death; the other SlSINAs are negative regulator and capable to suppress hypersensitive response cell death. Transgenic tomato plants overexpressing SlSINA2 exhibit pale‐green leaf phenotype, suggesting SlSINA2 regulates chlorophyll level in plant cells, whereas transgenic tomato plants overexpressing SlSINA5 have altered floral structure with exserted stigma, implicating SlSINA5 plays a role in flower development. [ABSTRACT FROM AUTHOR]

The plant-specific NAC ( NAM, ATAF1,2, CUC2) transcription factors play significant roles in diverse physiological processes. In this study, we determined the regulation of a stress-related tomato ( Solanum lycopersicum) NAC1 ( Sl NAC1) transcription factor at both the transcriptional and the post-translational level., The Sl NAC1 protein was found to be stable in the presence of proteasome-specific inhibitor MG132 or MG115 and ubiquitinated in plant cells, suggesting that the Sl NAC1 is subject to the ubiquitin-proteasome system-mediated degradation. Deletion analysis identified a short segment of 10 amino acids (aa261-270) that was required for ubiquitin-proteasome system-mediated degradation, among which two leucine residues (L268 and L269) were critical for the protein instability of Sl NAC1. Fusion of the degron ( Sl NAC1191-270) containing these 10 amino acids to green fluorescent protein was found to be sufficient to trigger the degradation of the fusion protein., In addition, the Sl NAC1 gene is strongly upregulated during Pseudomonas infection, while repression of the NAC1 ortholog in Nicotiana benthamiana resulted in enhanced susceptibility to Pseudomonas bacteria., These results suggest that rapid upregulation of the NAC1 gene resulting in more protein production is likely one of the strategies plants use to defend themselves against pathogen infection. [ABSTRACT FROM AUTHOR]