Glycosylation of S-RNases may influence pollen rejection thresholds in Solanum chacoense

A survey of Solanum chacoense plants expressing an authenticS₁₁-RNase transgene identified a line with partial compatibilityto S₁₁ pollen. By comparing fruit set to the S-RNase levelsdetermined immunologically in single styles, the minimum levelof S₁₁-RNase required for full rejection of S₁₁ pollen was estimatedto be 18 ng per style. The S₁₁-RNase threshold levels are thusconsiderably lower than those previously reported for the S₁₂-RNase.Interestingly, these two allelic S-RNases differ dramaticallyin the extent of glycosylation, with the number of glycosylationsites varying from one (S₁₁-RNase) to four (S₁₂-RNase). It issuggested that reduced glycosylation of the S₁₁-RNase may berelated to the lower threshold for pollen rejection. Key words: Gametophytic self-incompatibility, glycosylation, pistil-by-pistil analysis, S-RNase, Solanum chacoense, threshold Received 13 August 2007; Revised 27 November 2007 Accepted 30 November 2007