Requirement of KNAT1/BP for the Development of Abscission Zones in Arabidopsis thaliana

Abstract

The KNAT1 gene is a member of the Class I KNOX homeobox gene family and is thought to play an important role in meristem development and leaf morphogenesis. Recent studies have demonstrated that KNAT1/BP regulates the architecture of the inflorescence by affecting pedicle development in Arabidopsis thaliana. Herein, we report the characterization of an Arabidopsis T‐DNA insertion mutant that shares considerable phenotypic similarity to the previously identified mutant brevipedicle (bp). Molecular and genetic analyses showed that the mutant is allelic to bp and that the T‐DNA is located within the first helix of the KNAT1 homeodomain (HD). Although the mutation causes a typical abnormality of short pedicles, propendent siliques, and semidwarfism, no obvious defects are observed in the vegetative stage. A study on cell morphology showed that asymmetrical division and inhibition of cell elongation contribute to the downward‐pointing and shorter pedicle phenotype. Loss of KNAT/BP function results in the abnormal development of abscission zones. Microarray analysis of gene expression profiling suggests that KNAT1/BP may regulate abscission zone development through hormone signaling and hormone metabolism in Arabidopsis. (Managing editor: Ping He)

Arabidopsis Class I KNOTTED-Like Homeobox Proteins Act Downstream in the IDA-HAE/HSL2 Floral Abscission Signaling Pathway

“…Interestingly, EVR is downregulated in bp mutants (Wang et al, 2006); however, unlike bp ida-1 and bp-3 ida-2 ( Figure 1H; see Supplemental Figure 2 online), evr ida-2 mutants have defective abscission . Thus, EVR inhibits cell elongation and abscission independently of IDA, but BP/KNAT1 may mediate crosstalk between the IDA-HAE/HSL2 and the EVR pathways (Figure 8).…”

“…Floral organ abscission was not reestablished in bop1 bop2 bp-3 and bop1 bop2 bp ida-1 plants (see Supplemental Figures 3E and 3F online). Thus, mutations in BP/KNAT1 are not sufficient to initiate AZ formation, suggesting that the reported enlargement of floral AZs (Wang et al, 2006) is dependent on the presence of morphologically distinct AZ cells.…”

“…Floral organ abscission was not reestablished in bop1 bop2 bp-3 and bop1 bop2 bp ida-1 plants (see Supplemental Figures 3E and 3F online). Thus, mutations in BP/KNAT1 are not sufficient to initiate AZ formation, suggesting that the reported enlargement of floral AZs (Wang et al, 2006) is dependent on the presence of morphologically distinct AZ cells.Differences in pBS profiles between mutant and wild-type plants provide information as to where in the abscission process the mutation is exerting its effect (Patterson and Bleecker, 2004). The pBS of bp-3 and bp-10 was compared with that of Col wildtype and C24 wild-type plants, respectively.…”

“…This expression pattern suggests that BP/KNAT1 can have a role in both the initial stages of floral abscission, prior to organ dissociation, as well as regulating cell separation. It has been suggested that BP/KNAT1 could be involved in regulating AZ cell formation (Wang et al, 2006). Loss-of-function bop1 bop2 double mutants lack floral organ abscission due to an inability to specify the anatomy of AZ cells (McKim et al, 2008) (see Supplemental Figure 3D online).…”

Transgenic lines of Begonia maculata generated by ectopic expression of PttKN1

“…It has been studied extensively that KNOX genes play vital roles in the shoot apical meristem (SAM) function (Hake et al 2004;Norberg et al 2005;Wang et al 2006) and lateral meristem activity (Ko & Han 2004;Schrader et al 2004;Groover et al 2006) via maintaining the stem cell population. Class I KNOX genes were found to be necessary during all stages of the plant life (Jasinski et al 2006;Sakamoto et al 2006).…”