SABP2-interacting protein 428(SIP428) is a SIR2-type deacetylase, also called sirtuins. The SIP428 proteins belong to a family of NAD+-dependent deacetylase enzyme that was identified in tobacco. SABP2 is an important methyl esterase enzyme that catalyzes the conversion of methyl salicylic acid (MeSA) into salicylic acid (SA) during the pathogenic challenge. Accumulation of SA induces systemic acquired resistance (SAR), a broad-spectrum defense mechanism in other uninfected distal parts of the plant. Sirtuins play diverse roles in DNA repair, apoptosis, and stress responses. Cellular proteins are known to undergo posttranslational modifications such as methylation, phosphorylation, and ubiquitination. A more recent addition to the list is acetylation. Protein acetylation is a reversible modification that plays role in regulating transcription, activation, and deactivation of certain pathways by transferring acetyl group to lysine residues. This change neutralizes the positive charge of the amino group thereby affecting the biological function of the affected proteins. Preliminary research has shown that SIP428 is a non-histone deacetylase. To understand better about the role of SIP-428 in plant physiology and how it plays a vital role in SABP2 signaling pathway we will be using transgenic tobacco plant in which the expression of SIP 428 has been silenced/knocked down.

Abiotic stress poses a significant threat to crop productivity and food security. In this study, we focused on understanding the role of SIP-428, a SABP2-interacting protein, in mediating plant responses to environmental stresses. Transgenic tobacco plants overexpressing SIP-428 were subjected to salinity and drought stress. The overexpression of SIP-428 led to diminished growth under both stress conditions, indicating a negative impact on stress tolerance. Specifically, SIP-428 overexpression resulted in a reduction in catalase activity, while peroxidase activity remained unaffected. These findings suggest that SIP-428 plays a negative regulatory role on the catalase activity during abiotic stress, which may contribute to the susceptibility of plants to such stresses. Understanding the molecular mechanisms underlying SIP-428's role in stress responses could potentially lead to strategies for enhancing stress tolerance in crops, thereby promoting sustainable agricultural practices.

Salicylic acid is widely studied for its role in biotic stress signaling in plants. Several SA-binding proteins, including SABP2 (salicylic acid-binding protein 2) has been identified and characterized for their role in plant disease resistance. SABP2 is a 29 kDA tobacco protein that binds to salicylic acid with high affinity. It is a methylesterase enzyme that catalyzes the conversion of methyl salicylate into salicylic acid required for inducing a robust systemic acquired resistance (SAR) in plants. Methyl salicylic acid is one of the several mobile SAR signals identified in plants. SABP2-interacting protein 428 (SIP428) was identified in a yeast two-hybrid screen using tobacco SABP2 as a bait. In silico analysis shows that SIP428 possesses the SIR2 (silent information regulatory 2)-like conserved motifs. SIR2 enzymes are orthologs of sirtuin proteins that catalyze the NAD+-dependent deacetylation of Nε lysine-acetylated proteins. The recombinant SIP428 expressed in E. coli exhibits SIR2-like deacetylase activity. SIP428 shows homology to Arabidopsis AtSRT2 (67% identity), which is implicated in SA-mediated basal defenses. Immunoblot analysis using anti-acetylated lysine antibodies showed that the recombinant SIP428 is lysine acetylated. The expression of SIP428 transcripts was moderately downregulated upon infection by TMV. In the presence of SIP428, the esterase activity of SABP2 increased modestly. The interaction of SIP428 with SABP2, it's regulation upon pathogen infection, and similarity with AtSRT2 suggests that SIP428 is likely to play a role in stress signaling in plants.