Understanding the Role of Glyoxalase I During Pollen-Pistil Interaction in Brassicaceae

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Flowering plants (Angiosperms) have evolved mechanisms to recognize and select the right pollen. The stigma releases resources such as water and other compatibility factors needed for the compatible pollen to grow, while an incompatible (self-pollen) is recognized by the stigma and its growth and penetration is blocked through the mechanism called self-incompatibility (SI). SI is proposed to act by preventing compatibility factors from being delivered to the pollen thus preventing its growth through the stigma. Plants utilize SI to prevent inbreeding depression, and to promote genetic diversity and hybrid vigor. A haplotype specific interaction between the pollen-specific small cysteine-rich secreted protein (SP11/SCR) and stigma-specific S Receptor kinase (SRK) is known to lead to SI response in Brassica. While our understanding of the interactions between SRK and SP11/SCR is quite extensive, information pertaining to the subsequent signaling pathway that leads to the rejection response has remained unexplored. My thesis aims to advance our understanding of the downstream signaling pathway involved in the Brassica self-incompatibility response using canola (a major oil crop) as a model system. A detailed understanding of SI pathway in canola can allow the generation of new strategies to develop hybrid crops. Through this study, I have identified a compatibility factor; Glyoxalase I (GLO1) required for compatible pollination to occur and is targeted by the SI system. GLO1 carries out the detoxification of methylglyoxal (pyruvate aldehyde), an endogenous cytotoxic compound formed as a byproduct of glycolysis. Methylglyoxal (MG) reacts with proteins, nucleotides and basic phospholipids leading to the formation of AGEs (advanced glycation end-products). Hence, the operation of glyoxalase pathway to detoxify methylglyoxal and prevent its accumulation is of prime importance. Suppression of GLO1 in the compatible Brassica stigmas was sufficient to reduce compatibility, while overexpression of GLO1 in self-incompatible Brassica resulted in partial breakdown of SI response. GLO1 is post-translationally modified by its own substrate MG and MG modified GLO1 is efficiently targeted for proteasome-mediated degradation by ARC1 E3 ligase. Loss of GLO1 after SI results in increased MG levels and a concomitant increase in MG-modified proteins in the papillary cells leading to pollen rejection response.
Sankaranarayanan, S. (2015). Understanding the Role of Glyoxalase I During Pollen-Pistil Interaction in Brassicaceae (Doctoral thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca. doi:10.11575/PRISM/28574