Abstract
In autogamous plants like Arabidopsis (Arabidopsis thaliana), stamen filament elongation must be finely regulated to ensure that anthers reach the pistil at the correct developmental stage. In this work, we studied the roles of Arabidopsis TEOSINTE BRANCHED1, CYCLOIDEA, PCF15 (TCP15), and related class-I TCP transcription factors in stamen filament elongation. Plants with decreased expression of class-I TCPs and plants that express a fusion of TCP15 to a repressor domain (pTCP15::TCP15-EAR) had shorter stamens, indicating that class-I TCPs stimulate filament growth. These plants also showed reduced expression of several SMALL AUXIN UP RNA (SAUR)63 subfamily genes, which contain TCP target motifs in their promoters. Mutational analysis indicated that the TCP target motif in the SAUR63 promoter is required for expression of SAUR63 in stamen filaments. Moreover, TCP15 directly binds to the SAUR63 promoter region that contains the TCP target motif in vivo, highlighting the role of the TCPs in this process. Class-I TCPs are also required for the induction of SAUR63 subfamily genes by gibberellins (GAs). In addition, overexpression of SAUR63 restores filament growth in pTCP15::TCP15-EAR plants, whereas overexpression of TCP15 rescues the short stamen phenotype of GA-deficient plants. The results indicate that TCP15 and related class-I TCPs modulate GA-dependent stamen filament elongation by direct activation of SAUR63 subfamily genes through conserved target sites in their promoters. This work provides insight into GA-dependent stamen filament elongation.
Highlights
Plants with decreased expression of class-I TCP proteins (TCPs) and plants that express a fusion of TCP15 to a repressor domain had shorter stamens, indicating that class-I TCPs stimulate filament growth
TCPs Modulate Stamen Filament Elongation stamens is mediated by two jasmonic acid (JA)-inducible MYB transcription factors, MYB21 and MYB24 (Mandaokar et al, 2006), which are targeted by Jasmonate-ZIM domain proteins (Song et al, 2011)
We found a significant overlap between genes repressed in pTCP15::TCP15-EAR plants and those induced by ARF6 and ARF8
Summary
Plants with decreased expression of class-I TCPs and plants that express a fusion of TCP15 to a repressor domain (pTCP15::TCP15-EAR) had shorter stamens, indicating that class-I TCPs stimulate filament growth. Plants defective in auxin biosynthesis, transport, or perception and double mutants in the AUXIN RESPONSE FACTOR genes ARF6 and ARF8 show defects in stamen filament elongation and anther maturation (Nagpal et al, 2005; Cecchetti et al, 2008; Tashiro et al, 2009; Tabata et al, 2010; Reeves et al, 2012). GAs induce the synthesis of JA and the expression of MYB transcription factors to modulate stamen development; the short stamen phenotype of GA-deficient plants cannot be rescued by exogenous JA, suggesting that other GA-dependent, JA-independent pathways are required for correct stamen filament elongation (Cheng et al, 2009). The mechanism involved in this process is largely unknown
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