Classification and Structural Comparison of Full-Length cDNAs for Pathogenesis-Related Proteins

Area of Science:

• Plant Molecular Biology
• Plant Biochemistry
• Genomics

Background:

• Pathogenesis-related (PR) proteins are crucial in plant defense responses.
• Tobacco PR1 proteins, specifically PR1a and PR1b, are well-characterized but their gene family structure requires further elucidation.

Purpose of the Study:

• To characterize the diversity of tobacco PR1a and PR1b genes.
• To compare the sequence homology and structural features of PR1a and PR1b.

Main Methods:

• Isolation and classification of fourteen cDNA clones encoding PR1a and PR1b using restriction enzyme mapping.
• Partial sequencing of cDNA clones and comparison with known PR1a and PR1b amino acid sequences.
• Determination of full-length cDNA sequences for PR1a and PR1b and comparative sequence analysis.

Main Results:

• Classification of clones into two groups for PR1a and four for PR1b, indicating at least two PR1a and four PR1b mRNA types.
• Evidence for PR1 protein genes existing as a multigene family in the tobacco genome.
• High sequence homology (93% nucleotide, 91% amino acid) between PR1a and PR1b coding regions, with mature regions showing even higher homology (94% nucleotide, 93% amino acid).
• Signal peptide regions showed lower homology (80% nucleotide, 90% amino acid).
• Predicted secondary structures and hydropathy patterns suggest the C-terminus is important for PR1 protein function.

Conclusions:

• Tobacco possesses multiple genes encoding PR1a and PR1b proteins, forming a multigene family.
• PR1a and PR1b are highly homologous, especially in their mature functional domains.
• The C-terminal region of PR1 proteins likely plays a significant role in their biological function.