Arabidopsis AT-hook protein TEK positively regulates the expression of arabinogalactan proteins in controlling nexine layer formation in the pollen wall.

Nexine is a conserved layer of the pollen wall. We previously reported that the nexine layer is absent in the knockout mutant of TRANSPOSABLE ELEMENT SILENCING VIA AT-HOOK (TEK). In this work, we characterized the molecular function of TEK in pollen development and identified direct targets of TEK, Arabinogalactan proteins (AGPs), which are responsible for nexine formation. Electrophoretic mobility shift assay (EMSA) showed that TEK can directly bind to the nuclear matrix attachment region (MAR). Phenotypic similarity between tek and the TEK-SRDX transgenic lines indicated that TEK plays a role in transcriptional activation in anther development. Microarray analysis identified a total of 661 genes downstream of TEK, including four genes encoding AGPs, AGP6, AGP11, AGP23 and AGP40. Chromatin immunoprecipitation (ChIP) followed by PCR analysis using the FLAG-tagged TEK complement lines suggested that TEK is enriched in the promoters of these four genes. EMSA further confirmed that TEK binds to the AGP6 promoter. The expression of AGP6 driven by the TEK promoter in tek can partially rescue both nexine formation and plant fertility. These results show that TEK directly regulates AGPs expression in the anther. It is proposed that glycoproteins are an essential component of the nexine layer in the pollen wall.