Abstract
A gene encoding a KNOTTED1-LIKE HOMEOBOX PROTEIN1 (KD1) is highly expressed in both leaf and flower abscission zones. Reducing the abundance of transcripts of this gene in tomato (Solanum lycopersicum) by both virus-induced gene silencing and stable transformation with a silencing construct driven by an abscission-specific promoter resulted in a striking retardation of pedicel and petiole abscission. In contrast, Petroselinum, a semidominant KD1 mutant, showed accelerated pedicel and petiole abscission. Complementary DNA microarray and quantitative reverse transcription-polymerase chain reaction analysis indicated that regulation of abscission by KD1 was associated with changed abundance of genes related to auxin transporters and signaling components. Measurement of auxin content and activity of a DR5::β-glucuronidase auxin reporter assay showed that changes in KD1 expression modulated the auxin concentration and response gradient in the abscission zone.
Highlights
A gene encoding a KNOTTED1-LIKE HOMEOBOX PROTEIN1 (KD1) is highly expressed in both leaf and flower abscission zones
In our previous microarray studies, we found that three KNOTTED-LIKE HOMEOBOX (KNOX) genes, TOMATO KNOTTED3 (TKN3), TNK4, and KNOTTED1-LIKE HOMEOBOX PROTEIN1 (KD1), were highly expressed in the pedicel abscission zones (AZs) of tomato (Meir et al, 2010)
We found, in tomato, that KD1 is predominately expressed in the pedicel AZ (Meir et al, 2010)
Summary
A gene encoding a KNOTTED1-LIKE HOMEOBOX PROTEIN1 (KD1) is highly expressed in both leaf and flower abscission zones. Elimination or reduction in auxin flow by removal of the subtending organ (leaf or flower) or application of polar auxin transport inhibitors initiates abscission (Meir et al, 2010). KD1 Regulates Abscission (ARF1), ARF2, ARF7, and ARF19 show that these transcriptional regulators have functions in floral organ abscission (Ellis et al, 2005; Okushima et al, 2005) It is still unclear what mechanism modulates auxin level and auxin signaling in the AZ during the onset of abscission. A putative peptide ligand-receptor signal transduction pathway plays a role in the control of the onset of abscission in Arabidopsis (Cho et al, 2008; Stenvik et al, 2008). Analysis of inflorescence deficient in abscission (ida), haesa (hae) and haesa-like (hsl2) mutants in Arabidopsis indicated that IDA, a putative ligand, interacts with the receptor-like kinases HAE and HSL2 in regulating flower organ abscission (Jinn et al, 2000; Cho et al, 2008; Stenvik et al, 2008). In Arabidopsis, evidence suggests that IDA signaling represses the KNOTTED-LIKE HOMEOBOX (KNOX) family member KNOTTED-LIKE FROM ARABIDOPSIS THALIANA1 (KNAT1), which in turn, induces KNAT2 and KNAT6 to activate abscission (Shi et al, 2011)
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