Mikhail E. Nasrallah

Mikhail Elia Nasrallah is Professor Emeritus in the Plant Biology Section of the School of Integrative Plant Science] in the New York State College of Agriculture and Life Sciences at Cornell University.
==Education==
Nasrallah, a native of Kfarmishki, Lebanon, received a Bachelor of Science degree in Agriculture and a certification in Agronomy [Ingénieur Agricole] from the American University of Beirut in 1960, a Master's degree in Horticulture from the University of Vermont in 1962, and a doctorate degree in Plant Breeding and Genetics from Cornell University in 1965.
==Career and Research==
Nasrallah carried out postdoctoral research at Cornell University from 1965-1967 and had a faculty position in Genetics at the State University of New York Cortland from 1967 to 1985. He moved to Cornell as a Senior Research Associate in 1985 and joined the faculty at Cornell University in 1992 as a Professor of Plant Biology.
Much of Nasrallah's research has focused on the study of self-incompatibility in plants of the Brassicaceae (crucifer) family. Self-incompatibility (SI) is a post-pollination pre-zygotic genetic barrier widespread among angiosperms which ensures outcrossing by preventing selfing and mating among relatives. In several plant families including crucifers, SI is controlled by one genetic locus, designated the S locus, which exists as multiple variants, each of which encodes a distinct mating (SI) specificity. The highly selective SI barrier is based on the ability of cells of the pistil to discriminate between "self" pollen (i.e. pollen grains that express the same SI specificity as that expressed in the pistil, whether the grains are derived from the same flower, the same plant, or other plants that express the same SI specificity as the pistil) and "nonself" pollen (i.e. pollen that expresses an SI specificity different from that expressed in the pistil). Thus, in pollinations with "nonself" pollen, pollen grains produce tubes that grow through the pistil to the ovary where they fertilize the ovules, leading to seed production. By contrast, "self" pollen is inhibited along the path of pollen tube growth, thus preventing self-fertilization and seed production. In crucifers, the inhibition of "self" pollen occurs at the surface of the stigma, a structure located at the tip of the pistil whose epidermal cells capture pollen, such that pollen grains fail to hydrate and germinate or only produce short tubes that cannot penetrate into the pistil
As a doctoral student at Cornell, Nasrallah used a novel approach to the study of SI. Instead of the pollen-centric focus which at the time had been the norm in research aimed at identifying the molecular components of SI in various plant families, he focused on investigating the contribution of the pistil (specifically the stigma in crucifers) to specificity in the SI response. His immunochemical analysis of the extracts of stigmas derived from self-incompatible Brassica oleracea plants expressing different SI specificities led him to identify the S locus-specific antigen, which was the first molecule encoded by an SI specificity-determining locus to be identified. The success of this work would mark a paradigm shift in the study of SI across various plant families. Indeed, in subsequent years, identification of the pistil determinant of SI specificity preceded identification of the pollen specificity determinant by several years in various species of the Brassicaceae, Solanaceae, and Papaveraceae.
In further research on the Brassicaceae SI system carried out by the Nasrallah team at Cornell, the S locus-specific antigen, subsequently designated the S-locus glycoprotein, was used as a launching pad for a detailed analysis of the Brassica S locus, which determined that the S locus contains, not one gene, but two genes whose protein products determine specificity in the SI response. As a result of this work, S-locus variants, traditionally known as "S alleles", are now known as "S haplotypes". It is now well established that in the Brassicaceae, each S haplotype encodes matched variants of two proteins: the S-locus receptor kinase (SRK), a plasma membrane-spanning protein which is displayed at the surface of stigma epidermal cells,, and the S-locus cystine-rich protein (SCR), a small protein which is a component of the outer coat of the pollen grain,. Further biochemical analysis demonstrated a highly selective S haplotype-specific receptor-ligand relationship between SRK and SCR,. Because SCR will only bind the extracellular domain of the SRK encoded in the same S haplotype, it is only in a "self" pollination that SRK is activated and a signaling cascade is triggered which ultimately leads to the rejection of "self" pollen.
While SRK and SCR were first identified in Brassica, functional orthologues of these genes were also identified in Arabidopsis lyrata and subsequently in all self-incompatible crucifer species that have been analyzed to date,,,. By contrast, non-functional versions of the SRK and SCR genes were found in several geographical accessions of the self-fertile model plant Arabidopsis thaliana, suggesting that inactivation of these genes likely caused the switch to self-fertility in this species,,. In a landmark inter-specific transgenic complementation experiment, Nasrallah showed that the transgenic introduction of functional SRK-SCR gene pairs from self-incompatible A. lyrata into A. thaliana was sufficient to revert self-fertile A. thaliana to its ancestral state of SI. This pivotal experiment proved that SRK and SCR are the sole determinants, not only of SI specificity, but also of the out-crossing mode of mating in the Brassicaceae.
==Awards and Honors==
Nasrallah received the American University of Beirut's highest scholastic honor, the Penrose Award, in 1960; an award in Horticulture from the Burpee Foundation in 1961; and an award from the American Institute of Biological Sciences in 1970 in recognition of an outstanding research contribution related to a vegetable crop used for processing.
Category:Professors
Category:University of Vermont alumni
Category:Lebanese people