Chitinase genes responsive to cold encode antifreeze proteins in winter cereals

Area of Science:

• Plant molecular biology
• Cryobiology
• Biochemistry

Background:

• Antifreeze proteins (AFPs) are crucial for plant survival in cold climates.
• Winter rye (Secale cereale) accumulates AFP-like proteins during cold acclimation.
• Two chitinases, CHT9 and CHT46, were identified as potential AFPs.

Purpose of the Study:

• To investigate if cold-responsive chitinases in winter rye require post-translational modification for ice-binding activity.
• To characterize the function and genetic basis of these chitinases.

Main Methods:

• Isolation of cDNAs for two chitinases (CHT9 and CHT46) from cold-acclimated winter rye.
• Expression of mature chitinase sequences in Escherichia coli.
• Analysis of ice-binding activity of expressed proteins.
• Southern blot analysis to study gene families and chromosome mapping in wheat.

Main Results:

• CHT9 (class I) and CHT46 (class II) chitinases were identified, with predicted masses similar to purified plant chitinase-AFPs.
• Expressed CHT9 and CHT46 modified ice growth, confirming their ice-binding activity.
• Transcripts for both genes accumulated late during cold acclimation in winter rye.
• CHT46 homologs were found in a small gene family in winter rye and mapped to homeologous group 1 chromosomes in wheat, showing cold and drought-responsive expression.

Conclusions:

• Two novel cold-responsive chitinases with ice-binding activity were identified in winter rye.
• These chitinases do not require significant post-translational modification to bind ice.
• Gene duplication is proposed as the evolutionary mechanism for these antifreeze chitinases in cereals.