The Arabidopsis genome contains a great number of genes belonging to large families and in order to attribute a function to the different members of a same family of proteins, systematic analysis of insertion mutants in the corresponding genes have been initiated.
Initiation of transcription mediated by RNA polymerase II requires a number of transcription factors among which TFIID is the major core promoter recognition factor. TFIID is composed of highly conserved factors which include the TATA-binding protein (TBP) and around 14 TBP-associated factors (TAFs). Recently, the complete Arabidopsis TAF family has been identified. To obtain functional information about Arabidopsis TAFs, Lago and co-workers (2005) analyzed a T-DNA insertion mutant for AtTAF6. Detailed histologi-
cal and morphological analysis showed that the T-DNA insertion in AtTAF6 specifically affects pollen tube growth. Exploiting also an Arabidopsis T-DNA insertion mutant library, Mouline and co-workers (2002) have shown the predominant role of a K+ channel of the Shaker family (SPIK) in pollen tube development. Using a transposon (Ds/Spm) insertion-mutagenized collection, Goubet et al. (2003) have characterized an Arabidopsis mutant in the gene encoding AtCSLA7 of the cellulose synthase-like A subfamily. Analysis of the transmission efficiency of the insertion indicated that AtCSLA7 is important for pollen tube growth.
Apyrases hydrolyze nucleoside tri- and diphosphates are highly active and have been found in all pro- and eukaryotic organisms examined for their presence. In animals, these enzymes have been shown to play important regulatory roles in the mediation of signaling events. Two apyrases AtAPYl and AtAPY2 have been characterized in Arabidopsis (Steinebrunner et al. 2000) and T-DNA knockout lines for each apyrase have been isolated (Steinebrunner et al. 2003). The single lines apy1-1 and apy2-1 did not display a phe-notype under the conditions tested by the authors. However, the generation of the double knockouts apy1-1/apy2-1 shows that pollen not expressing any apyrase is unable to germinate. This work shows the importance of gene redundancy in pollen development and emphasizes the limits of the use of insertion mutant analysis for reverse genetics.
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