Ethylene-dependent and -independent pathways controlling floral abscission are revealed to converge using promoter::reporter gene constructs in the ida abscission mutant

Abstract

The process of floral organ abscission in Arabidopsis thaliana can be modulated by ethylene and involves numerous genes contributing to cell separation. One gene that is absolutely required for abscission is INFLORESCENCE DEFICIENT IN ABSCISSION, IDA, as the ida mutant is completely blocked in abscission. To elucidate the genetic pathways regulating floral abscission, molecular markers expressed in the floral abscission zone have been studied in an ida mutant background. Using plants with promoter-reporter gene constructs including promoters of a novel FLORAL ABSCISSION ASSOCIATED gene (FAA) encoding a putative single-stranded binding protein (BASIL), chitinase (CHIT::GUS) and cellulase (BAC::GUS), it is shown that IDA acts in the last steps of the abscission process. These markers, as well as HAESA, encoding a receptor-like kinase, were unaffected in their temporal expression patterns in ida compared with wild-type plants; thus showing that different regulatory pathways are active in the abscission process. In contrast to BASIL, CHIT::GUS and BAC::GUS showed, however, much weaker induction of expression in an ida background, consistent with a reduction in pathogen-associated responses and a lack of total dissolution of cell walls in the mutant. IDA, encoding a putative secreted peptide ligand, and HAESA appeared to have identical patterns of expression in floral abscission zones. Lastly, to address the role of ethylene, IDA::GUS expression in the wild type and the ethylene-insensitive mutant etr1-1 was compared. Similar temporal patterns, yet restricted spatial expression patterns were observed in etr1-1, suggesting that the pathways regulated by IDA and by ethylene act in parallel, but are, to some degree, interdependent.

TheBLADE-ON-PETIOLEgenes are essential for abscission zone formation inArabidopsis

“…Consistent with published results (Patterson and Bleecker, 2004;Butenko et al, 2006), CHIT::GUS was expressed in the floral organ AZ cells starting at position 4 and increased to maximal intensity, coincident with abscission at position 6, after which expression weakens (Fig. 6G).…”

“…For example, the promoter from an Arabidopsis abscission-related PG (PGAZAT) gene was able to drive floral organ AZ-specific expression of β-glucuronidase (GUS) during abscission (GonzalezCarranza et al, 2002). Furthermore, GUS constructs driven by the soybean (Glycine max) chitinase (CHIT) promoter or the bean (Phaseolus vulgaris) abscission cellulase (BAC) promoter are also upregulated in abscission zones during floral organ abscission (Bleecker and Patterson, 1997;Butenko et al, 2006;Chen and Bleecker, 1995;Patterson and Bleecker, 2004).…”

The EPIP Peptide of INFLORESCENCE DEFICIENT IN ABSCISSION Is Sufficient to Induce Abscission inArabidopsisthrough the Receptor-Like Kinases HAESA and HAESA-LIKE2

“…In analogy to CLV3, which is exported to the apoplastic space and binds the CLV1 receptor (Rojo et al, 2002;Ogawa et al, 2008) We have earlier proposed that IDA could be the ligand of the LRR-RLK HAE (Jinn et al, 2000;Butenko et al, 2003). IDA and HAE have overlapping expression patterns in the flower, and HAE is expressed at the base of the pedicel, where ectopic expression of IDA can induce abscission (Jinn et al, 2000;Butenko et al, 2006;Stenvik et al, 2006). As the hae hsl2 double mutant shows a strong defect in floral organ abscission ( Figures 3A and 3D), it is likely that the HAE antisense RNA that resulted in delayed abscission (Jinn et al, 2000) also silenced the endogenous expression of HSL2.…”

Floral organ abscission peptide IDA and its HAE/HSL2 receptors control cell separation during lateral root emergence

“…However, XTHs, EXPs, and PGs are expressed not only in the floral AZs but also at other sites of cell wall remodeling and breakdown, including the dehiscence zone (DZ) of the siliques, which undergo cell separation to allow seed shedding, and the cells overlaying emerging lateral roots (7)(8)(9)(10). IDA and HAE are also found expressed in DZs of mature siliques (11). We therefore hypothesized that IDA-HAE/HSL2 signaling might control other cellseparation processes than just floral organ abscission.…”