The use of a photoactivatable kaempferol analogue to probe the role of flavonol 3-O-galactosyltransferase in pollen germination

Flavonoids and Other Phenolic Compounds for Physiological Roles, Plant Species Delimitation, and Medical Benefits: A Promising View

Flavonoids and other phenolic constituents are a large group of plant metabolites that have long attracted interest from researchers worldwide due to their functions in plant physiology, as well as their huge number of benefits for human health and well-being. This review attempts to reveal a promising view of the major physiological roles of flavonoids and other phenolic phytochemical molecules, e.g., protection agents against UV damage, pathogen defense agents, detoxifying agents, and agents promoting pollen fertility and successful pollination. Besides, the value of both flavonoids and other phenolic phytochemicals for plant species delimitation was also emphasized for the first time with the determination of their major physiological roles. Furthermore, their medical benefits for mankind were also highlighted in this current work.

Identification of Wheat Inflorescence Development-Related Genes Using a Comparative Transcriptomics Approach

Inflorescence represents the highly specialized plant tissue producing the grains. Although key genes regulating flower initiation and development are conserved, the mechanism regulating fertility is still not well explained. To identify genes and gene network underlying inflorescence morphology and fertility of bread wheat, expressed sequence tags (ESTs) from different tissues were analyzed using a comparative transcriptomics approach. Based on statistical comparison of EST frequencies of individual genes in EST pools representing different tissues and verification with RT-PCR and RNA-seq data, 170 genes of 59 gene sets predominantly expressed in the inflorescence were obtained. Nearly one-third of the gene sets displayed differentiated expression profiles in terms of their subgenome orthologs. The identified genes, most of which were predominantly expressed in anthers, encode proteins involved in wheat floral identity determination, anther and pollen development, pollen-pistil interaction, and others. Particularly, 25 annotated gene sets are associated with pollen wall formation, of which 18 encode enzymes or proteins participating in lipid metabolic pathway, including fatty acid ω-hydroxylation, alkane and fatty alcohol biosynthesis, and glycerophospholipid metabolism. We showed that the comparative transcriptomics approach was effective in identifying genes for reproductive development and found that lipid metabolism was particularly active in wheat anthers.

Secret of the major birch pollen allergen Bet v 1: identification of the physiological ligand

The major birch pollen allergen Bet v 1 is the main elicitor of airborne type I allergies and belongs to the PR-10 family (pathogenesis-related proteins 10). Bet v 1 is the most extensively studied allergen, and is well characterized at a biochemical and immunological level; however, its physiological function remains elusive. In the present study, we identify Q3OS (quercetin-3-O-sophoroside) as the natural ligand of Bet v 1. We isolated Q3OS bound to Bet v 1 from mature birch pollen and confirmed its binding by reconstitution of the Bet v 1-Q3OS complex. Fluorescence and UV-visible spectroscopy experiments, as well as HSQC (heteronuclear single-quantum coherence) titration, and the comparison with model compounds, such as quercetin, indicated the specificity of Q3OS binding. Elucidation of the binding site by NMR combined with a computational model resulted in a more detailed understanding and shed light on the physiological function of Bet v 1. We postulate that the binding of Q3OS to Bet v 1 plays an important, but as yet unclear, role during the inflammation response and Bet v 1 recognition by IgE.

Structure-activity relationship studies of flavonol analogues on pollen germination

Flavonoids are polyphenolic compounds required in the fertilization process in many, if not all, plants. However, the exact biological mechanism(s) and the interacting proteins are unknown. To determine the characteristics important in activating or inhibiting the pollination sequence, a structure-activity relationship analysis of natural and synthetic flavonols was conducted. Flavonol analogues were synthesized through a modified "one-pot" procedure that utilized a Baker-Venkataraman type rearrangement and a Suzuki-Miyaura cross-coupling of a halo-flavonol with an organotrifluoroborate. Of the flavonols tested, kaempferol was the only compound to act as a full agonist. The other smaller, less sterically hindered flavonols (galangin, kaempferide, and 4'-methyl flavonol) acted as partial agonists. Larger more hydrophobic flavonol analogues (3'- and 4'-benzoyl, 3'- and 4'-phenyl, and 3'- and 4'-iodo flavonols) had minimal or no agonist activity. Competition assays between kaempferol and these minimally activating flavonols showed that these analogues inhibited the action of kaempferol in a manner consistent with noncompetitive antagonism. The results suggest that steric hindrance is the most important factor in determining a good agonist. Hydrogen bonding also had a positive effect as long as the substituent did not cause any steric hindrance.