PULLMAN, Wash. — Washington State University plant biologist Andrew G. McCubbin has co-authored an article published in the May 20 issue of Nature magazine (Vol. 429, 302-305).

In the article, “Identification of the Pollen Determinant of S-RNase-mediated Self-incompatibility,” MuCubbin and his co-authors report their research that resulted in identifying and describing the gene SLF, a key factor in preventing self-pollination in many plant species.

“In most plants, male and female reproductive organs are located close to each other within each flower and, unless there is a mechanism to prevent self-fertilization, this closeness leads to a tendency to inbreed,” McCubbin said. “On an evolutionary time scale, inbreeding leads to a loss of genetic variability and, hence, loss of adaptability, resulting in populations that are less capable of reacting to changing environmental conditions. About 40 percent of all plant species possess one of a variety of genetic systems (called self-incompatibility systems) to prevent inbreeding.”

The most widespread self-incompatibility system in plants is mediated by S-RNase (S-Ribonuclease) proteins, which are found in the female tissues. After pollination these proteins attack and degrade RNA within the pollen if it is genetically related to the female tissues through which it begins to extend a tube. This kills the pollen and prevents fertilization. A recognition event occurs between S-RNases and a previously undetermined pollen protein in the early stages of pollen tube growth. It is the outcome of this event that dictates whether or not fertilization will occur. “Our research identified SLF as the gene that interacts with the S-RNases. SLF either leaves the S-RNases intact to kill the pollen in the case of a ‘self-pollination,’ or defuses S-RNases by targeting them for degradation in a desirable cross-pollination.”

“There is commercial interest in this research,” McCubbin said. “It may be used to assist in breeding F1 (first generation) hybrid crop varieties that exhibit increased vigor and yield. The stronger varieties are achieved by crossing two inbred lines of a crop species. As almost all crop species are self-pollinating this requires removal of the pollen from the female parent. Currently this is achieved either by labor intensive, manual removal of the pollen producing anthers or by killing the pollen with chemical gametocides. By genetically engineering self-incompatibility into crop species, we may be able to use a naturally occurring system to do the same job in a more economic and/or less environmentally damaging way.”

The article covers work recently completed by a research team at Pennsylvania State University, of which McCubbin, then a postdoctoral researcher (1994-2001), was a member. The research was funded by a grant from the National Science Foundation and was led by Teh-hui Kao, professor of biochemistry and molecular biology at Pennsylvania State University.

McCubbin has been at WSU since 2001. His current work on pollen tube growth and plant breeding systems is supported the U.S. Department of Agriculture-National Research Initiative.

The article can be viewed online at http://www.nature.com/cgi-taf/DynaPage.taf?file=/nature/journal/v429/n6989/full/nature02523_fs.html