ASYMMETRIC LEAVES1 regulates abscission zone placement in Arabidopsis flowers

Abstract

BackgroundThe sepals, petals and stamens of Arabidopsis flowers detach via abscission zones formed at their boundaries with the underlying receptacle. The ASYMMETRIC LEAVES1 (AS1) MYB transcription factor plays a critical role in setting boundaries between newly formed leaf primordia and the shoot meristem. By repressing expression of a set of KNOTTED1-LIKE HOMEODOMAIN (KNOX) genes from developing leaf primordia, AS1 and its partner ASYMMETRIC LEAVES2 allow the patterning and differentiation of leaves to proceed. Here we show a unique role for AS1 in establishing the positions of the sepal and petal abscission zones in Arabidopsis flowers.ResultsIn as1 mutant flowers, the sepal abscission zones are displaced into inverted V-shaped positions, leaving behind triangular stubs of tissue when the organs abscise. Movement of the petal abscission zones is also apparent. Abscission of the medial sepals is delayed in as1 flowers; loss of chlorophyll in the senescing sepals contrasts with proximal zones that remain green. AS1 has previously been shown to restrict expression of the KNOX gene, BREVIPEDICELLUS (BP), from the sepals. We show here that loss of BP activity in as1 flowers is sufficient to restore the positions of the sepal and petal abscission zones, the sepal-receptacle boundary of the medial sepals and the timing of their abscission.ConclusionsOur results indicate that AS1 activity is critical for the proper placement of the floral organ abscission zones, and influences the timing of organ shedding.

Genome-wide identification of cassava R2R3 MYB family genes related to abscission zone separation after environmental-stress-induced abscission

“…AS1 regulates abscission zone placement in Arabidopsis flowers via restricting expression of the KNOX genes and BREVIPEDICELLUS (BP ) in the sepals. Moreover, abscission of the medial sepals is delayed in as1 flowers3536. Cassava MYB62 and Arabidopsis AS1 have been found to have high sequence similarity through blast analysis.…”

Abscission zone development in Setaria viridis and its domesticated relative, Setaria italica

“…In Arabidopsis , the AZ for floral organs forms at the boundary between the organ and the floral axis, in a region that exhibits low auxin levels (Gómez‐Mena and Sablowski, 2008; McKim et al, 2008; Gubert et al, 2014; Wang et al, 2016). However, it is unclear whether specification of a boundary is required for an AZ per se or whether it simply specifies the region within which abscission happens to occur in Arabidopsis flowers.…”

“…In most cases that have been examined in detail, the prospective AZ can be seen in section as a region of small, densely cytoplasmic cells (e.g., von Mohl, 1860a, 1860b; Addicott, 1982; Sexton and Roberts, 1982; Cho et al, 2008; McKim et al, 2008). This pattern has been documented in leaves of a disparate set of eudicots and a handful of monocots (von Mohl, 1860b; Pfeiffer, 1928; Gawadi and Avery, 1950; Addicott, 1982), in petals and stamens of Arabidopsis (McKim et al, 2008; Gómez‐Mena and Sablowski, 2008; Gubert et al, 2014), and in pedicels of fruits in tomato (Szymkowiak and Irish, 1999; Mao et al, 2000; Nakano et al, 2012). The AZ cells are generally appreciably smaller than those on either side of the AZ so that the position of the future AZ is unambiguous and often appears in cross section as a sharply defined region.…”

The IDA Peptide Controls Abscission in Arabidopsis and Citrus

“…After the formation of an AZ, which occurs early and simultaneously with the development of lateral organs from the apical meristem, the AZ cells can be distinguished from their neighbors by being small, densely cytoplasmic and lacking vacuoles ( Addicott, 1982 ; Sexton and Roberts, 1982 ; Osborne, 1989 ; Roberts et al, 2000 ; Liljegren, 2012 ). Once the abscission process is initiated these cells go through three sequential developmental stages; (i) cell fate determination and acquisition of competence to respond to abscission signals; (ii) cell wall loosening and expansion by cell wall remodeling (CWR) enzymes followed by organ separation; and (iii) differentiation of a protective lignified layer ( Patterson, 2001 ; Aalen et al, 2013 ; Gubert et al, 2014 ).…”