A Newly Identified Flower-Specific Splice Variant of <i>AUXIN RESPONSE FACTOR8</i> Regulates Stamen Elongation and Endothecium Lignification in Arabidopsis

Abstract

In addition to the full-length transcript <i>ARF8.1</i>, a splice variant (<i>ARF8.2</i>) of the auxin response factor gene <i>ARF8</i> has been reported. Here, we identified an intron-retaining variant of <i>ARF8.2</i>, <i>ARF8.4</i>, whose translated product is imported into the nucleus and has tissue-specific localization in <i>Arabidopsis thaliana</i> By inducibly expressing each variant in <i>arf8-7</i> flowers, we show that <i>ARF8.4</i> fully complements the short-stamen phenotype of the mutant and restores the expression of <i>AUX/IAA19</i>, encoding a key regulator of stamen elongation. By contrast, the expression of <i>ARF8.2</i> and <i>ARF8.1</i> had minor or no effects on <i>arf8-7</i> stamen elongation and <i>AUX/IAA19</i> expression. Coexpression of <i>ARF8.2</i> and <i>ARF8.4</i> in both the wild type and <i>arf8-7</i> caused premature anther dehiscence: We show that <i>ARF8.2</i> is responsible for increased expression of the jasmonic acid biosynthetic gene <i>DAD1</i> and that <i>ARF8.4</i> is responsible for premature endothecium lignification due to precocious expression of transcription factor gene <i>MYB26</i> Finally, we show that ARF8.4 binds to specific auxin-related sequences in both the <i>AUX/IAA19</i> and <i>MYB26</i> promoters and activates their transcription more efficiently than ARF8.2. Our data suggest that ARF8.4 is a tissue-specific functional splice variant that controls filament elongation and endothecium lignification by directly regulating key genes involved in these processes.