HAWAIIAN SKIRT: An F-Box Gene That Regulates Organ Fusion and Growth in Arabidopsis

Abstract

A fast neutron-mutagenized population of Arabidopsis (Arabidopsis thaliana) Columbia-0 wild-type plants was screened for floral phenotypes and a novel mutant, termed hawaiian skirt (hws), was identified that failed to shed its reproductive organs. The mutation is the consequence of a 28 bp deletion that introduces a premature amber termination codon into the open reading frame of a putative F-box protein (At3g61590). The most striking anatomical characteristic of hws plants is seen in flowers where individual sepals are fused along the lower part of their margins. Crossing of the abscission marker, Pro PGAZAT : b-glucuronidase, into the mutant reveals that while floral organs are retained it is not the consequence of a failure of abscission zone cells to differentiate. Anatomical analysis indicates that the fusion of sepal margins precludes shedding even though abscission, albeit delayed, does occur. Spatial and temporal characterization, using Pro HWS :b-glucuronidase or Pro HWS :green fluorescent protein fusions, has identified HWS expression to be restricted to the stele and lateral root cap, cotyledonary margins, tip of the stigma, pollen, abscission zones, and developing seeds. Comparative phenotypic analyses performed on the hws mutant, Columbia-0 wild type, and Pro 35S :HWS ectopically expressing lines has revealed that loss of HWS results in greater growth of both aerial and below-ground organs while overexpressing the gene brings about a converse effect. These observations are consistent with HWS playing an important role in regulating plant growth and development.

A Role for the F-Box Protein HAWAIIAN SKIRT in Plant microRNA Function

“…HWS is a 412-amino acid protein with an N-terminal F-box domain, a predicted transmembrane domain, and a C-terminal Kelch-2 domain ( Fig. 1; González-Carranza et al, 2007). The typical MIM156 phenotype was restored in mutants transformed with a genomic construct of HWS, confirming that HWS was indeed the causal locus (Fig.…”

“…Mutations in HWS affect root growth via regulation of quiescentcenter independent meristem activity as well as stomatal guard cell development Kim et al, 2016). Due to delayed abscission, hws mutants also fail to shed sepals, petals, and anthers (González-Carranza et al, 2007). Loss of HWS furthermore results in increased organ growth, whereas overexpression yields smaller plants with elongated, serrated, and hyponastic leaves (González-Carranza et al, 2007).…”

“…Due to delayed abscission, hws mutants also fail to shed sepals, petals, and anthers (González-Carranza et al, 2007). Loss of HWS furthermore results in increased organ growth, whereas overexpression yields smaller plants with elongated, serrated, and hyponastic leaves (González-Carranza et al, 2007).…”

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

“…RT-PCR results indicated that IDA, HAESA and HAWAIIAN SKIRT had the same expression levels in bop1 bop2 and wild-type flowers (results not shown). Whereas mutation in HAWAIIAN SKIRT leads to delayed abscission and fusion of sepal margins that precludes shedding (Gonzalez-Carranza et al, 2007), downregulation of IDA or HAESA results in abscission defects only (Jinn et al, 2000;Butenko et al, 2003). The RT-PCR results were confirmed by quantitative PCR for IDA and HAESA; the expression level in wild-type (Col-0) and bop1 bop2 floral AZs did not differ as the relative expression was very close to 1: 0.94 for IDA and 0.95 for HAESA (see Fig.…”

“…Although considerably delayed, floral organ abscission occurs in ethylene-insensitive mutants of Arabidopsis, suggesting that ethylene signalling is important for the timing of abscission but is not essential for it to occur (Patterson and Bleecker, 2004). Numerous loci are proposed to modulate floral organ abscission in Arabidopsis, including HAESA (Jinn et al, 2000), AGAMOUS-LIKE 15 (Fernandez et al, 2000), the DELAYED ABSCISSION loci (Patterson and Bleecker, 2004), genes for the actin-related proteins ARP4 and ARP7 (Kandasamy et al, 2005b;Kandasamy et al, 2005a), several AUXIN RESPONSE FACTOR genes (Ellis et al, 2005;Okushima et al, 2005), INFLORESCENCE DEFICIENT IN ABSCISSION (IDA) (Butenko et al, 2003), and HAWAIIAN SKIRT (Gonzalez-Carranza et al, 2007). Disruption of the expression of these genes results in delayed floral organ abscission, with the exception of ida plants, which retain floral organs indefinitely (Butenko et al, 2003).…”