June Nasrallah

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June Nasrallah is Barbara McClintock Professor in the Plant Biology Section of the School of Integrative Plant Science at Cornell University. [1] Her research focuses on plant reproductive biology and the cell-cell interactions that underlie self-incompatibility in plants belonging to the mustard (Brassicaceae) family. [2] 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. [2] [3]

Contents

Education

Nasrallah received her B.Sc. degree in Biology from the American University of Beirut, Lebanon and her Ph.D. in Genetics from Cornell University, [1] where her doctoral research focused on the characterization of Neurospora genes involved in fungal reproduction.

Career and research

Nasrallah, in collaboration with Mikhail Nasrallah, also a member of the faculty at Cornell University, initiated a research program in plant reproduction aimed at understanding the highly specific cell-cell interactions between pollen and pistil (the female reproductive structure) that ultimately lead either to successful pollination and seed production or to inhibition of pollen tube growth and failure to set seed. The focus of their research is self-incompatibility, a general term that encompasses several independently-evolved pre-zygotic genetic mechanisms that prevent self-fertilization when a pollination involves pistil and pollen that express the same variant of one or more self-incompatibility loci. Self-incompatibility is manifested by the lack of seed set resulting from disruption of germination of pollen grains or growth of pollen tubes within the pistil as they proceed from the stigma towards the ovules. In essence, self-incompatibility mechanisms are highly specific self/nonself mate recognition systems which confer on cells of the pistil the ability to discriminate between pollen grains that are defined as “self” and “nonself” on the basis of genetic identity at self-incompatibility loci, resulting in specific inhibition of “self” pollen.

The existence of self-incompatibility was appreciated by early scientists, including Charles Darwin, who recognized it as a natural system that serves to promote hybrid vigor in several plant species and as a major driver of plant evolution. The genetics and cytological manifestations of self-incompatibility were well worked out for several plant families by the middle of the twentieth century. However, a mechanistic understanding of self-incompatibility had to await the advent of molecular approaches in the 1980s. The Nasrallah laboratory applied these approaches to investigate the self-incompatibility system of the Brassicaceae. It had been shown that specificity of the self-incompatibility response in this family is controlled by a single locus called the S locus and that “self” pollen is arrested at the surface of stigma epidermal cells resulting in the failure of pollen germination and pollen tube growth into the pistil. By analyzing self-incompatibility in Brassica species and building on the immunochemical identification of stigma proteins that segregated with the S locus, [4] [5] 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), [6] a transmembrane protein expressed in stigma epidermal cells, and the second gene encodes the S-locus cystine-rich (SCR), [7] 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). [8] 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 . [9]  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 [10] 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, [11] results that were confirmed by high-resolution structural analysis of the SRK-SCR complex in Jijie Chai’s laboratory. [12] Additionally, analysis of SRK-SCR transformants of various Arabidopsis thaliana accessions [13] identified the genetic basis of some of the processes responsible for transitions from out-crossing to self-fertilizing modes of mating in Arabidopsis thaliana [14] [15] [16] and more generally in the Brassicaceae family. [17]

Honors and awards

Related Research Articles

<span class="mw-page-title-main">Brassicaceae</span> Family of flowering plants

Brassicaceae or Cruciferae is a medium-sized and economically important family of flowering plants commonly known as the mustards, the crucifers, or the cabbage family. Most are herbaceous plants, while some are shrubs. The leaves are simple, lack stipules, and appear alternately on stems or in rosettes. The inflorescences are terminal and lack bracts. The flowers have four free sepals, four free alternating petals, two shorter free stamens and four longer free stamens. The fruit has seeds in rows, divided by a thin wall.

<i>Arabidopsis thaliana</i> Model plant species in the family Brassicaceae

Arabidopsis thaliana, the thale cress, mouse-ear cress or arabidopsis, is a small plant from the mustard family (Brassicaceae), native to Eurasia and Africa. Commonly found along the shoulders of roads and in disturbed land, it is generally considered a weed.

<span class="mw-page-title-main">Fertilisation</span> Union of gametes of opposite sexes during the process of sexual reproduction to form a zygote

Fertilisation or fertilization, also known as generative fertilisation, syngamy and impregnation, is the fusion of gametes to give rise to a zygote and initiate its development into a new individual organism or offspring. While processes such as insemination or pollination, which happen before the fusion of gametes, are also sometimes informally referred to as fertilisation, these are technically separate processes. The cycle of fertilisation and development of new individuals is called sexual reproduction. During double fertilisation in angiosperms, the haploid male gamete combines with two haploid polar nuclei to form a triploid primary endosperm nucleus by the process of vegetative fertilisation.

<span class="mw-page-title-main">Calmodulin</span> Messenger protein

Calmodulin (CaM) (an abbreviation for calcium-modulated protein) is a multifunctional intermediate calcium-binding messenger protein expressed in all eukaryotic cells. It is an intracellular target of the secondary messenger Ca2+, and the binding of Ca2+ is required for the activation of calmodulin. Once bound to Ca2+, calmodulin acts as part of a calcium signal transduction pathway by modifying its interactions with various target proteins such as kinases or phosphatases.

<span class="mw-page-title-main">Pollen tube</span> Tubular structure to conduct male gametes of plants to the female gametes

A pollen tube is a tubular structure produced by the male gametophyte of seed plants when it germinates. Pollen tube elongation is an integral stage in the plant life cycle. The pollen tube acts as a conduit to transport the male gamete cells from the pollen grain—either from the stigma to the ovules at the base of the pistil or directly through ovule tissue in some gymnosperms. In maize, this single cell can grow longer than 12 inches (30 cm) to traverse the length of the pistil.

<span class="mw-page-title-main">Self-pollination</span> Form of pollination

Self-pollination is a form of pollination in which pollen arrives at the stigma of a flower or at the ovule of the same plant. The term cross-pollination is used for the opposite case, where pollen from one plant moves to a different plant.

Self-incompatibility (SI) is a general name for several genetic mechanisms that prevent self-fertilization in sexually reproducing organisms, and thus encourage outcrossing and allogamy. It is contrasted with separation of sexes among individuals (dioecy), and their various modes of spatial (herkogamy) and temporal (dichogamy) separation.

<span class="mw-page-title-main">Heterostyly</span> Two different types of flowers (style) on same plant

Heterostyly is a unique form of polymorphism and herkogamy in flowers. In a heterostylous species, two or three morphological types of flowers, termed "morphs", exist in the population. On each individual plant, all flowers share the same morph. The flower morphs differ in the lengths of the pistil and stamens, and these traits are not continuous. The morph phenotype is genetically linked to genes responsible for a unique system of self-incompatibility, termed heteromorphic self-incompatibility, that is, the pollen from a flower on one morph cannot fertilize another flower of the same morph.

Leptosphaeria maculans is a fungal pathogen of the phylum Ascomycota that is the causal agent of blackleg disease on Brassica crops. Its genome has been sequenced, and L. maculans is a well-studied model phytopathogenic fungus. Symptoms of blackleg generally include basal stem cankers, small grey lesions on leaves, and root rot. The major yield loss is due to stem canker. The fungus is dispersed by the wind as ascospores or rain splash in the case of the conidia. L. maculans grows best in wet conditions and a temperature range of 5–20 degrees Celsius. Rotation of crops, removal of stubble, application of fungicide, and crop resistance are all used to manage blackleg. The fungus is an important pathogen of Brassica napus (canola) crops.

Peptide signaling plays a significant role in various aspects of plant growth and development and specific receptors for various peptides have been identified as being membrane-localized receptor kinases, the largest family of receptor-like molecules in plants. Signaling peptides include members of the following protein families.

HOTHEAD is an Arabidopsis thaliana gene that encodes a flavin adenine dinucleotide-containing oxidoreductase. This gene has a role in the creation of the carpel during the formation of flowers through the fusion of epidermal cells. Observations of reversion of the hothead phenotype and genotype led to the suggestion that the plants were able to "remember" the sequences of genes present in their ancestors, possibly through a cache of complementary RNA. This report attracted broad attention, and alternative explanations were suggested. Later research suggested that the supposed reversion phenomenon was due to the plants having a pronounced bias towards outcrossing, rather than self-fertilizing at high rates, as is typical for A. thaliana.

Arabinogalactan-proteins (AGPs) are highly glycosylated proteins (glycoproteins) found in the cell walls of plants. Each one consists of a protein with sugar molecules attached. They are members of the wider class of hydroxyproline (Hyp)-rich cell wall glycoproteins, a large and diverse group of glycosylated wall proteins.

Arabidopsis thaliana is a first class model organism and the single most important species for fundamental research in plant molecular genetics.

Feronia, also known as FER or protein Sirene, is a recognition receptor kinase found in plants. FER plays a significant part in the plant immune system as a receptor kinase which assists in immune signaling within plants, plant growth, and plant reproduction. FER is regulated by the Rapid Alkalinization Factor (RALF). FER regulates growth in normal environments but it is most beneficial in stressful environments as it helps to initiate immune signaling. FER can also play a role in reproduction in plants by participating in the communication between the female and male cells. FER is found in and can be studied in the organism Arabidopsis thaliana.

Cysteine-rich proteins are small proteins that contain a large number of cysteines. These cysteines either cross-link to form disulphide bonds, or bind metal ions by chelation, stabilising the protein's tertiary structure. CRPs include a highly conserved secretion peptide signal at the N-terminus and a cysteine-rich region at the C-terminus.

Christian Dumas is a French biologist born on January 2, 1943. He is a professor at the École normale supérieure (ENS) in Lyon. Dumas has devoted himself to the study of the specific sexual reproduction mechanisms of flowering plants and their applications for the genetic improvement of cultivated plants. He is also the scientific director of the botanical garden of the Parc de la Tête d'Or in Lyon.

<span class="mw-page-title-main">Distyly</span>

Distyly is a type of heterostyly in which a plant demonstrates reciprocal herkogamy. This breeding system is characterized by two separate flower morphs, where individual plants produce flowers that either have long styles and short stamens, or that have short styles and long stamens. However, distyly can refer to any plant that shows some degree of self-incompatibility and has two morphs if at least one of the following characteristics is true; there is a difference in style length, filament length, pollen size or shape, or the surface of the stigma. Specifically these plants exhibit intra-morph self-incompatibility, flowers of the same style morph are incompatible. Distylous species that do not exhibit true self-incompatibility generally show a bias towards inter-morph crosses - meaning they exhibit higher success rates when reproducing with an individual of the opposite morph.

Vernonica "Noni" Elsa Franklin-Tong is an English plant cell biologist who is Emeritus Professor at the University of Birmingham. She is known for her studies on self-incompatibility in Papaver rhoeas. In 2021 she was elected a Fellow of the Royal Society.

<span class="mw-page-title-main">Wisconsin Fast Plants</span> Cultivar of Brassica rapa

Wisconsin Fast Plants is the registered trademark for a cultivar of Brassica rapa, developed as a rapid life-cycle model organism for research and teaching. Wisconsin Fast Plants are a member of the Brassicaceae family, closely related to the turnip and bok choy. Wisconsin Fast Plants were developed in accordance with an ideotype for an ideal model organism to be used in expediting plant research. Similarly, their rapid life cycle and other model organism characteristics made them easy to grow in large numbers in classrooms. For the last few decades they have been grown in classrooms and laboratories around the world.

Mikhail Elia Nasrallah is a plant scientist, specialising in the genetics of self-incompatibility in flowering plants. He 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.

References

  1. 1 2 "June Nasrallah | Plant Biology Section". plantbio.cals.cornell.edu. Retrieved 2020-11-09.
  2. 1 2 "June Nasrallah". www.nasonline.org. Retrieved 2020-11-09.
  3. ↑ Brownlee, C. (2004-01-19). "Biography of June B. Nasrallah". Proceedings of the National Academy of Sciences. 101 (4): 909–910. doi: 10.1073/pnas.0400056101 . ISSN   0027-8424. PMC   330090 . PMID   16576757.
  4. ↑ Nasrallah, M. E.; Wallace, D. H. (1967). "Immunochemical Detection of Antigens in Self-incompatibility Genotypes of Cabbage". Nature. 213 (5077): 700–701. Bibcode:1967Natur.213..700N. doi:10.1038/213700a0. ISSN   1476-4687. S2CID   4174539.
  5. ↑ Hinata, K.; Nishio, T.; Kimura, J. (1982). "Comparative Studies on S-Glycoproteins Purified from Different S-Genotypes in Self-Incompatible BRASSICA Species II. Immunological Specificities". Genetics. 100 (4): 649–657. doi:10.1093/genetics/100.4.649. ISSN   0016-6731. PMC   1201839 . PMID   17246075.
  6. ↑ Nasrallah, J. B.; Stein, J. C.; Kandasamy, M. K.; Nasrallah, M. E. (1994-12-02). "Signaling the arrest of pollen tube development in self-incompatible plants". Science. 266 (5190): 1505–1508. Bibcode:1994Sci...266.1505N. doi:10.1126/science.266.5190.1505. ISSN   0036-8075. PMID   17841712. S2CID   11914223.
  7. ↑ Schopfer, C. R.; Nasrallah, M. E.; Nasrallah, J. B. (1999-11-26). "The male determinant of self-incompatibility in Brassica". Science. 286 (5445): 1697–1700. doi:10.1126/science.286.5445.1697. ISSN   0036-8075. PMID   10576728.
  8. ↑ Kachroo, A.; Schopfer, C. R.; Nasrallah, M. E.; Nasrallah, J. B. (2001-09-07). "Allele-specific receptor-ligand interactions in Brassica self-incompatibility". Science. 293 (5536): 1824–1826. Bibcode:2001Sci...293.1824K. doi:10.1126/science.1062509. ISSN   0036-8075. PMID   11546871. S2CID   21033636.
  9. ↑ Nasrallah, Mikhail E.; Liu, Pei; Nasrallah, June B. (2002-07-12). "Generation of Self-Incompatible Arabidopsis thaliana by Transfer of Two S Locus Genes from A. lyrata". Science. 297 (5579): 247–249. Bibcode:2002Sci...297..247N. doi:10.1126/science.1072205. ISSN   0036-8075. PMID   12114625. S2CID   10606974.
  10. ↑ Boggs, Nathan A.; Dwyer, Kathleen G.; Shah, Paurush; McCulloch, Amanda A.; Bechsgaard, Jesper; Schierup, Mikkel H.; Nasrallah, Mikhail E.; Nasrallah, June B. (2009). "Expression of distinct self-incompatibility specificities in Arabidopsis thaliana". Genetics. 182 (4): 1313–1321. doi:10.1534/genetics.109.102442. ISSN   1943-2631. PMC   2728868 . PMID   19506308.
  11. ↑ Boggs, Nathan A.; Dwyer, Kathleen G.; Nasrallah, Mikhail E.; Nasrallah, June B. (2009-05-12). "In vivo detection of residues required for ligand-selective activation of the S-locus receptor in Arabidopsis". Current Biology. 19 (9): 786–791. doi:10.1016/j.cub.2009.03.037. ISSN   1879-0445. PMC   2747293 . PMID   19375322.
  12. ↑ Ma, Rui; Han, Zhifu; Hu, Zehan; Lin, Guangzhong; Gong, Xinqi; Zhang, Heqiao; Nasrallah, June B.; Chai, Jijie (2016). "Structural basis for specific self-incompatibility response in Brassica". Cell Research. 26 (12): 1320–1329. doi:10.1038/cr.2016.129. ISSN   1748-7838. PMC   5143417 . PMID   27824028.
  13. ↑ Nasrallah, M. E.; Liu, P.; Sherman-Broyles, S.; Boggs, N. A.; Nasrallah, J. B. (2004-11-09). "Natural variation in expression of self-incompatibility in Arabidopsis thaliana: implications for the evolution of selfing". Proceedings of the National Academy of Sciences of the United States of America. 101 (45): 16070–16074. Bibcode:2004PNAS..10116070N. doi: 10.1073/pnas.0406970101 . ISSN   0027-8424. PMC   528763 . PMID   15505209.
  14. ↑ Tang, Chunlao; Toomajian, Christopher; Sherman-Broyles, Susan; Plagnol, Vincent; Guo, Ya-Long; Hu, Tina T.; Clark, Richard M.; Nasrallah, June B.; Weigel, Detlef; Nordborg, Magnus (2007-08-24). "The evolution of selfing in Arabidopsis thaliana". Science. 317 (5841): 1070–1072. Bibcode:2007Sci...317.1070T. doi:10.1126/science.1143153. ISSN   1095-9203. PMID   17656687. S2CID   45853624.
  15. ↑ Liu, Pei; Sherman-Broyles, Susan; Nasrallah, Mikhail E.; Nasrallah, June B. (2007-04-17). "A cryptic modifier causing transient self-incompatibility in Arabidopsis thaliana". Current Biology. 17 (8): 734–740. doi:10.1016/j.cub.2007.03.022. ISSN   0960-9822. PMC   1861850 . PMID   17412590.
  16. ↑ Boggs, Nathan A.; Nasrallah, June B.; Nasrallah, Mikhail E. (2009). "Independent S-locus mutations caused self-fertility in Arabidopsis thaliana". PLOS Genetics. 5 (3): e1000426. doi: 10.1371/journal.pgen.1000426 . ISSN   1553-7404. PMC   2650789 . PMID   19300485.
  17. ↑ Nasrallah, June B. (2017). "Plant mating systems: self-incompatibility and evolutionary transitions to self-fertility in the mustard family". Current Opinion in Genetics & Development. 47: 54–60. doi: 10.1016/j.gde.2017.08.005 . ISSN   1879-0380. PMID   28915488.
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