Identification of genes required for pollen‐stigma recognition in Arabidopsis thaliana

Abstract

In higher plants, cell-cell recognition reactions taking place following pollination allow the selective restriction of self-pollination and/or interspecific pollination. Many of these systems function by regulating the process of water transfer from the cells found at the stigmatic surface to the individual pollen grain. Interspecific pollination studies on the cruciferous weed Arabidopsis thaliana revealed only a broad specificity of pollen recognition such that pollen from all tested members of the crucifer family were recognized, whereas pollen from almost all other species failed to hydrate. Genetic analysis of A. thaliana has identified three genes that are essential for this recognition process. Recessive mutations in any of these genes result in male sterility due to the production of pollen grains that fail to hydrate when placed on the stigma, but that are capable of hydrating and growing a pollen tube in vitro. Results from mixed pollination experiments suggest that the mutant pollen grains specifically lack a functional pollen-stigma recognition system. All three mutations described also result in a defect in the wax layer normally found on stems and leaves, similar to previously described eceriferum (cer) mutations. Genetic complementation and mapping experiments demonstrated that the newly identified mutants are allelic to the previously identified genes cer1, cer3 and cer6. TEM analysis of the ultrastructure of the pollen coating revealed that all of the mutant pollen grains bear coatings of normal thickness and that tryphine lipid droplets are missing in cer1-147, are reduced in size in cer6-2654 and appear normal in cer3-2186.(ABSTRACT TRUNCATED AT 250 WORDS)

Pollen and Stigma Structure and Function: The Role of Diversity in Pollination

“…In plants with dry stigmas, regulated pollen hydration provides an effective early barrier to incompatible pollination. This mode is active in selfincompatible crosses (Sarker et al, 1988) and in crosses between species (Lewis and Crowe, 1958;Hü lskamp et al, 1995). These processes are remarkably localized: the stigma can hydrate a compatible grain while restricting the hydration of foreign or incompatible pollen on the same papillus (Dickinson, 1995).…”

“…Disrupting pollen coat lipids or pollen coat proteins in Brassicaceae species can delay or block pollen hydration. In particular, mutations that impair long-chain lipid synthesis, and consequently the proper assembly of the pollen coating, severely reduce the hydration of Arabidopsis pollen and result in male sterility (Preuss et al, 1993;Hü lskamp et al, 1995). Hydraulic contact can be restored to these mutant grains by the addition of purified triacylglycerides .…”

Signaling Events in Pollen Acceptance or Rejection in the Arabidopsis Species

“…Once a compatible pollen grain comes in contact with a stigmatic papilla, the early stages of pollen capture and adhesion, pollen hydration, and germination are closely regulated (Elleman et al 1992 ;Preuss et al 1993 ;Kandasamy et al 1994 ;Zinkl et al 1999 ). The ability to conduct genetic screens with relative ease in A. thaliana has aided in identifying a number of factors that regulate pollen-stigma interactions (Preuss et al 1993 ;Hulskamp et al 1995 ;Nishikawa et al 2005 ).…”

“…The importance of pollen coat lipids in the hydration process was determined by the study of impaired pollen hydration in A. thaliana eceriferum ( cer ) mutants (Preuss et al 1993 ;Hulskamp et al 1995 ). The cer mutants have defects in the long-chain lipid synthesis, and there was a reduction or loss of pollen coat on the surface of the cer mutant pollen grains.…”

“…The cer mutants have defects in the long-chain lipid synthesis, and there was a reduction or loss of pollen coat on the surface of the cer mutant pollen grains. As a result, these pollen grains failed to hydrate on the stigma, but this defect could be rescued by high environmental humidity where normal pollen hydration, pollen tube growth, and successful seed set were observed (Preuss et al 1993 ;Hulskamp et al 1995 ). Thus, work on the cer and fdh mutants suggests that long-chain lipids are required on both surfaces (i.e., the pollen and the stigma) to support pollen hydration.…”