The role of AmRLK in cell shaping

Gouveia, Andrea Costa Veludo (2005) The role of AmRLK in cell shaping. Doctoral thesis, University of East Anglia.

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Abstract

The production of brightly coloured flowers is thought to be one of many strategies employed by plants to attract pollinators. In Antirrhinum majus, flower colour is largely determined by the presence of anthocyanin in the epidermal cells of their petals. However, the conical shape of these cells also enhances the colour intensity of the pigmentation. The inactivation of MIXTA, a MYB transcription factor, inhibits conical cell formation in the petal epidermis (Noda et al., 1994). The dull colour of petals in mixta mutant flowers demonstrates the degree to which cell form can influence pigmentation intensity. Unravelling and characterising the targets of MIXTA should reveal how MIXTA directs changes in cell shape. This in turn should provide a model to understand cell expansion events in more complex systems. A differential-display PCR using mRNA from wild type and mixta mutant flowers identified a gene encoding a novel receptor like kinase (AmRLK), up regulated in the mixta mutant of Antirrhinum (Bhatt, 2001 ).

This thesis characterises the role of AmRLK in cell shaping and its relationship with MIXTA. AmRLK is expressed in the epidermis of petals of wild type Antirrhinum flowers when conical cells initiate. AmRLK transcript levels are elevated in the absence of MIXTA and lower in MIXTA overexpressing lines, suggesting that MIXTA represses AmRLK. Experiments using a 5' promoter region of AmRLK to drive GUS expression in tobacco, suggested that this repression operates through the AmRLK promoter. Functional analysis suggested that AmRLK is sufficient to induce conical cell formation. The silencing of an AmRLK homologue in N. benthamiana, NbRLK, resulted in inhibition of proper conical cell expansion in petals. Furthermore, the overexpression of AmRLK in Nicotiana tabaccum induced outgrowth formation in normally flat carpel epidermal cells, redirecting the polarity of growth. Analysis of a AmRLK:YFP protein fusion in tobacco epidermal cells suggested that AmRLK is polarly localised in the plasma membrane of expanding conical cells and root hair cells, consistent with a function of AmRLK in cell expansion and shaping. A model whereby AmRLK initiates the process of conical cell formation and MIXTA directs the formation of full grown conical cells is proposed.

Item Type:	Thesis (Doctoral)
Faculty \ School:	Faculty of Science
Depositing User:	Chris White
Date Deposited:	26 Aug 2026 08:20
Last Modified:	26 Aug 2026 08:20
URI:	https://ueaeprints.uea.ac.uk/id/eprint/104353
DOI:

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