“Self or non-self”: Pollen rejection in Nicotiana
In Solanaceae, self-incompatibility (SI) is under the S-locus control, which encodes both the female (S-RNase) and male determinants (a suite of SLF proteins). However, other non-S-locus linked genes such as HT-B, 120K, NaStEP, NaTrxh, and NaSIPP are essential for SI. NaStEP encodes a stigma-specific protein that exhibits a dual activity as a protease inhibitor and voltage channel blocker. NaStEP is taken up by pollen tubes (PT). Loss of function assays show that NaStEP suppression disrupts pollen rejection in an S-specific manner. Another crucial pistil protein for SI is called HT-B. It is degraded in PTs from compatible crosses but not in SI ones. However, in the absence of NaStEP, HT-B is degraded inside PTs no matter if the cross is compatible or incompatible. It suggests that NaStEP protects HT-B from degradation, probably with its proteinase inhibitor activity.
We looked for NaStEP PT protein interactors by Y2H. We recovered a mitochondrial phosphate carrier called NaSIPP, which is specific and highly abundant in mature pollen of SI Nicotiana species. A loss of function approach showed that NaSIPP is essential to SI and BiFC assays demonstrated that interaction of NaStEP with NaSIPP occurs in the PT mitochondria. We propose a new model for the pollen rejection response in Nicotiana.
Felipe Cruz-García studied biology at the Faculty of Sciences of the National Autonomous University of Mexico (UNAM). He obtained his Ph.D. degree in Biochemistry at UNAM. From 1997 to 2000, he completed a postdoctoral stay in Molecular Genetics at the University of Missouri-Columbia at McClure´s lab, USA. He is currently a Full Professor at the School of Chemistry and a tutor of the Postgraduate in Biochemical Sciences of the UNAM. Dr. Cruz has graduated 16 Bachelor’s, 10 Master’s, and 8 Doctorate students in Biochemical Sciences. He has taught 45 undergraduate and graduate courses in his teaching activity, ranging from Mathematics, Cell Biology, Biochemistry, Genetics, and Molecular Biology. Since 2000, he has investigated the molecular mechanisms underlying the pollen rejection response in Nicotiana. Scientific contributions are around 50 publications in journals such as Nature, Plant Physiology, New Phytologist, Journal of Biological Chemistry, Structural Biology. For his academic and research work, he has been distinguished by the National System of Researchers with level II and with the highest distinction of the Program of Performance Bonuses for Academic Staff (PRIDE) of Full Time with level “D” by the UNAM.