Genetic interaction between glabra3‐shapeshifter and siamese in Arabidopsis thaliana converts trichome precursors into cells with meristematic activity

Abstract

SummaryThe identity of many genes required for trichome differentiation is known. This paper describes a novel interaction between mutant alleles of two such genes. One of the alleles, called gl3-sst, is derived from the GL3 locus, which encodes a basic helix-loop-helix type transcription factor. The mutation in the gl3-sst protein modifies its ability to form a complex with the GL1 protein (a MYB transcription factor required for trichome formation), leading to changes in gene expression compared with wild type during gl3-sst mutant trichome development. The other mutant allele, sim, is a likely loss of function allele derived from the SIM locus, which is predicted to encode a negative regulator of D-type cyclin activity. The gl3-sst sim double mutant exhibits mounds of cells derived from the proliferation of single trichome precursors. The ectopic expression of a D-type cyclin gene in gl3-sst mimics the double mutant phenotype. Thus, an interaction between altered trichome gene expression caused by the gl3-sst mutation and relaxed regulation of D-type cyclin activity in the double mutant converted a non-dividing cell into a novel highly proliferating cell type.

A Systems Approach Reveals Regulatory Circuitry for Arabidopsis Trichome Initiation by the GL3 and GL1 Selectors

“…Consistent with SIM being a direct target of GL3, the levels of SIM expression in gl3 egl3 plants were found to be very significantly reduced [51]. Our results, highlighting a role of GL1 in the regulation of endoreduplication early during trichome initiation, is consistent with the recent identification of sim mutant allele as a modifier of the trichome phenotype of an allele of GL3 ( gl3-sst ) impaired in its ability to interact with GL1 [9],[53]. RBR1, through its interaction with members of the E2F family of transcription factors, regulates the balance between cell division and the endocycle, and the conditional inactivation of RBR1 results in trichomes with altered morphologies, which include more branches [54].…”

Transcriptome Analysis of Arabidopsis Wild-Type and gl3–sst sim Trichomes Identifies Four Additional Genes Required for Trichome Development

“…An example of such a gene is GL1 , which is more highly expressed in young developing trichomes than in mature trichomes (Larkin et al, 1993). We have previously shown that the clusters of cells that compose gl3–sst sim trichomes have many attributes of early-stage trichomes, including elevated GL1 expression (Marks et al, 2007). Thus, we wished to determine whether other genes needed for early trichome development were more highly expressed in the double mutant trichomes.…”

“…Interestingly, sim trichomes continue to divide after initiation, but then develop into fairly normal trichomes (Walker et al, 2000). As described in Marks et al (2007), gl3–sst sim trichomes are composed of large clusters of cells that rarely advance beyond stage two. These trichomes also exhibit greatly enhanced GL1 expression, which normally decreases as trichomes mature.…”

“…During stage six, trichome expansion ceases (see Supplemental Figure 1 for representative images of many of these stages). Other cellular events associated with the progression through the stages include endoreduplication of the nuclear DNA to an average of 32–64C during stages one through four, vacuolization during the transition from stage four to five, and the development of surface papillae during stages five and six (Marks, unpublished data; Hulskamp et al, 1994; Marks et al, 2007). …”

“…The focus of this report is on the transcriptome profiles of mature wild-type leaf trichomes and those of the glabra3–shapeshifter ( gl3–sst ) siamese ( sim ) double mutant (Marks et al, 2007). The gl3–sst mutation results in a reduced interaction between GL1 and the altered GL3 bHLH protein (Esch et al, 2003).…”