Table 1.

Mechanistic differences for S-RNase-based SI between subfamily Prunoideae of Rosaceae and Solanaceae, Plantaginaceae and subfamily Maloideae

Family	Subfamily	Competitive interaction	Defects in SLF/SFB	Potential number of genes for pollen specificity	Proposed function of SLF/SFB
Rosaceae	Prunoideae	No*	SC†	Single	Protect self S-RNase from being degraded
Rosaceae	Maloideae	Yes	Not reported	Multiple	Mediate degradation of non-self S-RNases
Solanaceae		Yes	Not reported	Multiple	Mediate degradation of non-self S-RNases
Plantaginaceae		Yes	Not reported	Multiple	Mediate degradation of non-self S-RNases

* Huang et al. (2008) reported the only case of competitive interaction in tetraploid Prunus pseudocerasus, but the breakdown of SI could have been caused by mutations in other SI-related genes (Tao and Iezzoni, 2010).

^† SC (self-compatible) indicates breakdown of SI in pollen.