ABERRANT TESTA SHAPE encodes a KANADI family member, linking polarity determination to separation and growth of Arabidopsis ovule integuments

Abstract

SummaryThe Arabidopsis aberrant testa shape (ats) mutant produces a single integument instead of the two integuments seen in wild-type ovules. Cellular anatomy and patterns of marker gene expression indicate that the single integument results from congenital fusion of the two integuments of the wild type. Isolation of the ATS locus showed it to encode a member of the KANADI (KAN) family of putative transcription factors, previously referred to as KAN4. ATS was expressed at the border between the two integuments at the time of their initiation, with expression later confined to the abaxial layer of the inner integument. In an inner no outer (ino) mutant background, where an outer integument does not form, the ats mutation led to amorphous inner integument growth. The kan1 kan2 double mutant exhibits a similar amorphous growth of the outer integument without affecting inner integument growth. We hypothesize that ATS and KAN1/KAN2 play similar roles in the specification of polarity in the inner and outer integuments, respectively, that parallel the known roles of KAN proteins in promoting abaxial identity during leaf development. INO and other members of the YABBY gene family have been hypothesized to have similar parallel roles in outer integument and leaf development. Together, these two hypotheses lead us to propose a model for normal integument growth that also explains the described mutant phenotypes.

Regulation of planar growth by the Arabidopsis AGC protein kinase UNICORN

“…The early oblique or periclinal cell divisions likely include asymmetric cell divisions because early differences in gene expression and morphology indicate that cells of the two cell layers rapidly adopt different fates ( Fig. 1 I and M) (7,(14)(15)(16)(17). Thus, each integument exhibits tissue polarity and consists of an upper, or adaxial, and lower, or abaxial, cell layer.…”

“…Class III HD-ZIP, KAN, and YABBY transcription factors play central roles in the establishment of adaxial-abaxial polarity in leaves (36,37) and ovules (38), with KAN genes promoting abaxial cell fate and lamina outgrowth in leaves (26,27). ATS is a KAN gene that regulates integument boundary formation, inner integument outgrowth, and adaxialabaxial polarity (15,28,29,38). A role for UCN in establishing adaxial-abaxial polarity in integuments is unlikely given the unaltered spatial expression pattern of several marker genes in ucn.…”

“…ATS encodes a putative transcription factor (15) of the KANADI (KAN) family (26,27). Defects in ats mutants are specific to ovules, which show congenitally fused integuments (15,28,29). In wild-type ovules, ATS expression is observed at the boundary between the two initiating integuments, at the abaxial side of the inner integument and the adaxial side of the outer integument, and eventually becomes restricted to the abaxial cells of the inner integument (15) (Fig.…”

Embryogenesis: Pattern Formation from a Single Cell

“…The KANADI genes, KAN1, 2, and 3 (but not KAN4) are initially expressed throughout the early globular stage embryo, but their domain of expression becomes restricted to the basal peripheral region. By the heart stage this domain comes to mark the basal abaxial portion of the cotyledon primordia (Fig 15E, F, G) (Eshed et al, 2004;McAbee et al, 2006). A triple mutant kan1 kan2 kan4 displays an enlarged SAM as well as a loss of adaxial-abaxial polarity of the cotyledons.…”

Of Blades and Branches: Understanding and Expanding the Arabidopsis Ad/Abaxial Regulatory Network through Target Gene Identification

“…3I). Conversely, loss of KANADI function causes ectopic cotyledon formation from the hypocotyl (Izhaki and Bowman 2007), whereas extra KANADI function represses outgrowth of the integuments that form the seed coat (McAbee et al 2006).…”