Hypervariable Domains of Self-Incompatibility RNases Mediate Allele-Specific Pollen Recognition

Area of Science:

• Plant reproductive biology
• Molecular genetics
• Biochemistry

Background:

• Self-incompatibility (SI) is a crucial genetic mechanism in angiosperms that promotes outcrossing by preventing self-pollen germination.
• In Solanaceae, SI is governed by a multiallelic S-locus, with the S-RNase being its sole known product.
• S-RNases possess conserved and hypervariable regions, hypothesized to be involved in catalytic activity and allelic specificity, respectively.

Purpose of the Study:

• To investigate the role of S-RNase hypervariable regions in determining allelic specificity in Solanum chacoense.
• To confirm whether specific amino acid substitutions in hypervariable regions can alter SI phenotype.

Main Methods:

• Transgenic expression of S11-RNase in Solanum chacoense (S12S14 genotype) to observe pollen rejection.
• Construction of a chimeric S11 gene with substitutions in hypervariable regions based on S13-RNase.
• Transformation of S12S14 plants with the chimeric gene to assess the resulting SI phenotype.

Main Results:

• Transgenic plants expressing S11-RNase exhibited rejection of S11 pollen, confirming functional SI.
• Plants transformed with the chimeric S11 gene, containing S13-specific residues in hypervariable regions, acquired the S13 SI phenotype.
• This indicates that even minor changes in hypervariable regions significantly impact S-RNase function and allelic specificity.

Conclusions:

• The hypervariable regions of S-RNases are the primary determinants of allelic specificity in Solanum self-incompatibility.
• Amino acid residues within these regions directly control the recognition and rejection of specific S-alleles.
• This finding provides critical insights into the molecular mechanisms underlying plant reproductive isolation and SI evolution.