June Nasrallah

June Nasrallah is Barbara McClintock Professor in the Plant Biology Section of the School of Integrative Plant Science at Cornell University. Her research focuses on plant reproductive biology and the cell-cell interactions that underlie self-incompatibility in plants belonging to the mustard (Brassicaceae) family. She was elected to the US National Academy of Sciences in 2003 for this work and her contributions generally to our understanding of receptor-based signaling in plants.

Early life and education Nasrallah was born and raised in Beirut, Lebanon. She studied at Collège Protestant Français and at the French Language Section of International College, Beirut, graduating with a Lebanese and a French Baccalauréat.

Nasrallah received a B.Sc. degree in Biology from the American University of Beirut and her Ph.D. in Genetics from Cornell University, the Nasrallah group demonstrated that the recognition of "self" pollen is based on the activity of two highly polymorphic, co-adapted, and tightly-linked genes contained within the S locus. One gene encodes the S-locus receptor kinase (SRK), a transmembrane protein expressed in stigma epidermal cells, and the second gene encodes the S-locus cystine-rich (SCR), a small diffusible peptide component of the outer pollen coating. Thus, the S locus was shown to be a complex locus and its variants, which had been called S alleles, are now more appropriately referred to as S haplotypes.

Subsequent biochemical experiments demonstrated that SCR is the ligand for the SRK receptor and that the SRK-SCR interaction is S-haplotype specific (i.e. it only occurs when the SRK and SCR proteins are encoded in the same S haplotype). Consequently, it is only when the stigma is pollinated with "self" pollen that SCR can bind and activate its cognate SRK, thus triggering a signaling cascade within stigma epidermal cells that ultimately leads to arrest of pollen germination and tube growth.

An important development in the study of self-incompatibility in the Brassicaceae was the successful transfer of the SI trait into the normally self-fertile model plant Arabidopsis thaliana by transformation with SRK-SCR gene pairs from self-incompatible A. lyrata and Capsella grandiflora. Not only did this successful experiment provide proof that the SRK and SCR genes are the sole determinants of self-incompatibility specificity, but it also opened novel avenues of research. The introduction of several SI specificities into A. thaliana allowed in planta functional analysis of in vitro-generated receptor and ligand variants and identification of the specific amino-acid residues responsible for productive SRK-SCR interactions, results that were confirmed by high-resolution structural analysis of the SRK-SCR complex in Jijie Chai's laboratory. Additionally, analysis of SRK-SCR transformants of various Arabidopsis thaliana accessions identified the genetic basis of some of the processes responsible for transitions from out-crossing to self-fertilizing modes of mating in Arabidopsis thaliana and more generally in the Brassicaceae family.

Honors and awards

Elected member of the US National Academy of Sciences (2003) Recipient of the Martin Gibbs Medal from the American Society of Plant Biologists (2003) Awarded an Honorary Doctorate in Humane Letters from the American University of Beirut (2023) for her significant contribution to the study of plant self-incompatibility and evolutionary transitions to self-fertility in the Brassicaceae President and Founding Member of the Lebanese Academy of Sciences