Petunia nectar proteins have ribonuclease activity

Area of Science:

• Plant biology
• Biochemistry
• Molecular evolution

Background:

• Insect-pollinated plants produce nectar as a reward.
• Nectar requires antimicrobial properties to prevent microbial growth.
• Nicotiana spp. nectar uses hydrogen peroxide for antimicrobial activity, but Petunia hybrida shows limited hydrogen peroxide production despite antibacterial properties.

Purpose of the Study:

• To investigate the mechanism behind the antibacterial properties of Petunia hybrida nectar.
• To compare nectar proteins between Petunia hybrida and ornamental tobacco.
• To identify and characterize novel proteins responsible for nectar's antimicrobial activity.

Main Methods:

• Comparative analysis of nectar protein profiles between Petunia hybrida and ornamental tobacco.
• Identification and cloning of genes encoding RNase T2 proteins from Petunia hybrida.
• Analysis of protein sequences and expression patterns of identified RNases.

Main Results:

• Significant differences in protein profiles and functions were found between Petunia hybrida and ornamental tobacco nectar.
• Unique RNase activities were identified in Petunia hybrida nectar.
• Four RNase T2 proteins were cloned, with RNase Phy3 and RNase Phy4 exhibiting unique characteristics intermediate between S- and S-like RNases.

Conclusions:

• Petunia nectar possesses antibacterial properties mediated by unique RNase enzymes, distinct from the hydrogen peroxide mechanism in Nicotiana.
• The identified RNases (Phy3 and Phy4) represent a novel class of nectar proteins with potential roles in defense.
• The findings support the evolutionary hypothesis that S-RNases may have evolved from defense RNases in floral tissues.