Coordinate Gene Activity in Response to Agents That Induce Systemic Acquired Resistance

Area of Science:

• Plant pathology
• Molecular biology
• Plant immunity

Background:

• Pathogen infection can induce a generalized disease resistance in previously uninfected plant tissues.
• Systemic acquired resistance (SAR) is a key plant immunity mechanism, exemplified by tobacco's response to tobacco mosaic virus.
• SAR involves plants developing a disease-resistant state after a hypersensitive reaction to a pathogen.

Purpose of the Study:

• To investigate the molecular mechanisms underlying the induction of systemic acquired resistance (SAR).
• To identify the genes and signaling pathways involved in SAR.
• To explore the role of salicylic acid in SAR induction.

Main Methods:

• Analysis of mRNA expression patterns during SAR induction.
• Treatment with salicylic acid to observe its effect on gene expression.
• Application of a synthetic compound (methyl-2,6-dichloroisonicotinic acid) to assess its impact on resistance and gene expression.

Main Results:

• The onset of SAR was found to correlate with the coordinated induction of nine classes of mRNAs, termed 'SAR genes'.
• Salicylic acid, a potential endogenous signal, was shown to induce the expression of these same SAR genes.
• A synthetic compound, methyl-2,6-dichloroisonicotinic acid, effectively induced both SAR and SAR gene expression.

Conclusions:

• Induced resistance in plants, including SAR, is likely mediated by the coordinated expression of specific SAR genes.
• Pathogen-induced necrosis plays a role in the biosynthesis of salicylic acid, which in turn triggers SAR.
• The findings support a model where salicylic acid acts as a crucial signal in the cascade leading to plant immunity.