S-RNase-based self-incompatibility in Petunia inflata

Abstract

The protein-degradation model invokes specific degradation of non-self S-RNases in the pollen tube mediated by an SLF, and can explain compatible versus incompatible pollination and the phenomenon of competitive interaction, where SI breaks down in pollen carrying two different S-alleles. In Solanaceae, Plantaginaceae and subfamily Maloideae of Rosaceae, there also exist multiple S-locus-linked SLF/SFB-like genes that potentially function as the pollen S-gene. To date, only three such genes, all in P. inflata, have been examined, and they do not function as the pollen S-gene in the S-genotype backgrounds tested. Interestingly, subfamily Prunoideae of Rosaceae appears to possess only a single SLF/SFB gene, and competitive interaction, observed in Solanaceae, Plantaginaceae and subfamily Maloideae, has not been observed. Thus, although the cytotoxic function of S-RNase is an integral part of SI in Solanaceae, Plantaginaceae and Rosaceae, the function of SLF/SFB may have diverged. This highlights the complexity of the S-RNase-based SI mechanism. The review concludes by discussing some key experiments that will further advance our understanding of this self/non-self discrimination mechanism.

Self-Incompatibility System of Ipomoea trifida, a Wild-Type Sweet Potato

“…In S -RNase-based GSI, S -RNases are abundantly expressed in the transmitting tract of the style, and they directly inhibit the growth of self-pollen tubes (Lee et al 1994 ). The pollen determinant genes, SFB / SLF and related genes, are expressed in developing pollen grains and pollen tubes (Ushijima et al 2003 ;Entani et al 2003 ;Sijacic et al 2004 ;Sassa et al 2007Sassa et al , 2010Meng et al 2010 ;Kakui et al 2011 ), and they recognize self or non-self S -RNases (Meng et al 2010 ;Sassa et al 2010 ). In Papaver plants, the female S -gene product, PrsS, is an extracellular signaling molecule that acts as a ligand to the self male S -gene product, PrpS, a transmembrane ion-channel/receptor.…”

Protein Interactions in S-RNase-Based Gametophytic Self-Incompatibility

“…Chromosome-walking, differential display or degenerate PCR-cloning approaches Wang et al, 2003Wang et al, ,2004Wheeler & Newbigin 2007;Zhou et al, 2003) in the Solanaceae and Plantaginaceae identified a number of SLF-like genes (SLFL) that were linked to the S-locus. These genes were thought not to be involved in self-incompatibility interactions specifically, since they did not show interaction with known S-RNases nor did they exhibit competitive interaction in transgenic assays (Hua et al, 2007;Meng et al, 2011). Hua et al, (2007) attempted to identify domains of SLF proteins that governed allelic specificity by iterative pairwise comparisons of SLF proteins with SLFL proteins.…”

Cloning and Bioinformatics Analysis of <i>Rosa rugose S</i> Locus F-Box Gene (<i>RrSLF</i>)

“…Many researchers believe that the pollenspecific SFB/SLF gene can encode for F-box proteins that can specific recognize and ubiquitinate heterogenous S-RNase, resulting in compatible reaction between pistil and pollen [10] [11] [12]. The discovery of pollen-specific SFB/SLF gene facilitates the investigation into the mechanism of GSI reaction, but further experiments are needed to prove that the F-box proteins are involved in the interaction between SCF complex and substrate protein [13] [14] [15] [16]. The plant species identified with self-incompatibility are generally those with partial self-incompatibility at different levels.…”