Two genes encode the two subunits of cottonseed catalase

Area of Science:

• Plant Molecular Biology
• Enzymology
• Genetics

Background:

• Catalase enzymes are crucial for plant defense against oxidative stress.
• Cottonseed catalase exists as multiple developmentally distinct subunits.
• Previous work identified SU 1, predominantly synthesized in 1-day-old cotyledons.

Purpose of the Study:

• To isolate and sequence the cDNA encoding a developmentally distinct subunit of cottonseed catalase.
• To characterize the gene structure and expression of catalase subunits in cotton.
• To investigate the peroxisomal targeting signals of catalase subunits.

Main Methods:

• Construction and screening of a cDNA library from 3-day-old dark-grown cotton cotyledons.
• Nucleotide sequencing and sequence comparison of catalase subunit cDNAs.
• In vitro transcription and translation, followed by isoelectric focusing and SDS-PAGE.
• Southern blot analysis of cotton genomic DNA.

Main Results:

• A 1.8-kb cDNA encoding a 492-amino acid peptide (SU 2) was isolated.
• SU 2 cDNA sequence shows 76% nucleotide and 92% amino acid identity to SU 1.
• Cotton genome contains at least two catalase genes: one for SU 1 and at least two for SU 2.
• A peroxisomal targeting signal was identified upstream of the C-terminus of SU 2.

Conclusions:

• Cotton cotyledons possess at least two distinct genes encoding catalase subunits.
• The identified SU 2 subunit is developmentally regulated and distinct from SU 1.
• The study proposes a potential location for peroxisomal targeting signals in catalase subunits lacking the canonical C-terminal motif.