No abstract

No abstract

Mate selection and maintenance of genetic diversity is crucial to successful reproduction and species survival. Plants utilize self-incompatibility system as a genetic barrier to prevent self pollen from developing on the pistil, leading to hybrid vigor and diversity. In Brassica (canola, kale, and broccoli), an allele-specific interaction between the pollen SCR/SP11 (S-locus cysteine rich protein/S locus protein 11) and the pistil S Receptor Kinase, results in the activation of SRK which recruits the Arm Repeat Containing 1 (ARC1) E3 ligase to the proteasome. The targets of Arm Repeat Containing 1 are proposed to be compatibility factors, which when targeted for degradation by Arm Repeat Containing 1 results in pollen rejection. Despite the fact that protein degradation is predicted to be important for successful self-pollen rejection, the identity of the various proteins whose abundance is altered by the SI pathway has remained unknown. To identify potential candidate proteins regulated by the SI response, we have used the two-dimensional difference gel electrophoresis analysis, coupled with matrix-assisted laser desorption ionization/time of flight/MS. We identified 56 differential protein spots with 19 unique candidate proteins whose abundance is down-regulated following self-incompatible pollinations. The identified differentials are predicted to function in various pathways including biosynthetic pathways, signaling, cytoskeletal organization, and exocytosis. Recognition of suitable pollen is a key aspect of reproductive success of angiosperms. Despite having little control over the type of pollen that lands on the stigma of the pistil, many plant species have developed elaborate recognition systems to allow the growth of only suitable pollen grains and to reject genetically similar (self-incompatible) and incompatible mates in order to increase the probability of successful reproduction and survival. Adherence of compatible pollen grains to the stigmatic papillae results in early signaling events leading to hydraulic connectivity with the stigma, which facilitates movement of water into the pollen grains. Following hydration, pollen grains germinate and produce tubes that penetrate the stigmatic cell walls and traverse the pistil down to the ovules where fertilization takes place (1, 2). In species of Brassicaceae (canola, broccoli, cabbage, Arabidopsis), which are characterized by dry stigmas, this recognition occurs at the earliest stages of pollen adhesion and hydration. Only compatible pollen is capable of inducing the stigma to release its resources such as water and other factors necessary for pollen growth, whereas incompatible pollen is blocked either prior to hydration or during attempts to penetrate the stigmatic barrier (3). Although multiple genetic screens have identified various compatible pollen factors necessary for the initial recognition mechanisms, the molecules or mechanisms behind delivery of stigma factors necessary to support pollen growth remain largely unknown (3, 4). The lipids o...

In addition to a family of structurally related proteins encoded by the Granule lattice (GRL) genes, the dense core granules in Tetrahymena thermophila contain a second, more heterogeneous family of proteins that can be defined by the presence of a domain homologous to beta/gamma-crystallins. The founding members of the family, Induced during Granule Regeneration 1 (IGR1) and Granule Tip 1 (GRT1), were identified in previous screens for granule components. Analysis of the recently sequenced T. thermophila macronuclear genome has now uncovered 11 additional related genes. All family members have a single beta/gamma-crystallin domain, but the overall predicted organization of family members is highly variable, and includes three other motifs that are conserved between subsets of family members. To demonstrate that these proteins are present within granules, polypeptides from a subcellular fraction enriched in granules were analyzed by mass spectrometry. This positively identified four of the predicted novel beta/gamma-crystallin domain proteins. Both the functional evidence for IGR1 and GRT1 and the variability in the overall structure of this new protein family suggest that its members play roles that are distinct from those of the GRL family.

No abstract