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

A survey of Solanum chacoense plants expressing an authentic S-11-RNase transgene identified a line with partial compatibility to S-11 pollen. By comparing fruit set to the S-RNase levels determined immunologically in single styles, the minimum level of S-11-RNase required for full rejection of S-11 pollen was estimated to be 18 ng per style. The S-11-RNase threshold levels are thus considerably lower than those previously reported for the S-12-RNase. Interestingly, these two allelic S-RNases differ dramatically in the extent of glycosylation, with the number of glycosylation sites varying from one (S-11-RNase) to four (S-12-RNase). It is suggested that reduced glycosylation of the S-11-RNase may be related to the lower threshold for pollen rejection.