Arabidopsis Thaliana AT-hook Gene TEK Regulates Arabian Galactose Protein AGPs To Control Pollen Outer Wall Development

Nexine is a conserved layer of pollen wall. We previous identified that anAT-hook/PPC domain-containing protein in Arabidopsis, TRANSPOSABLE ELEMENTSILENCING VIA AT-HOOK (TEK)，regulates nexine formation. In this work, wecharacterized the molecular function of TEK and nexine components based on theidentification of TEK regulated genes. Phenotype similarity between tek and theTEK-SRDX transgenic lines indicated that TEK functions as a transcriptional activator.Electrophoretic mobility shift assay (EMSA) showed that TEK can directly bind tonuclear matrix attachment region (MAR). Microarray analysis identified a total of661genes downstream of TEK, including four genes encoding arabinogalactan-proteins(AGPs), AGP6, AGP11, AGP23and AGP40. Quantitive RT-PCR analysis confirmed thedownregulation of these genes in tek. Chromatin immunoprecipitation (ChIP)followed by PCR analysis using the FLAG-tagged TEK complement lines suggestedthat TEK is enriched in the promoters of these four genes. EMSA further confirmedthat TEK binds to AGP6promoter. The agp6-1point mutant showed reduced fertilitywith defective nexine formation. The expression of AGP6driven by TEK promoter intek can partially rescue the nexine formation and plant fertility. These resultsindicated that TEK directly regulates AGPs expression in anther. We propose thatAGPs form the backbone of the nexine with various polysaccharides linked to AGPs.