TheseirenaB Class Floral Homeotic Mutant of California Poppy (Eschscholzia californica) Reveals a Function of the Enigmatic PI Motif in the Formation of Specific Multimeric MADS Domain Protein Complexes

Matthias Lange,Annette Becker,Günter Theißen,Rainer Melzer,Sabrina Lange,Svetlana Orashakova,David R Smyth

doi:10.1105/tpc.112.105809

Matthias Lange, Annette Becker + Show 5 more

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https://doi.org/10.1105/tpc.112.105809

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Abstract

The products of B class floral homeotic genes specify petal and stamen identity, and loss of B function results in homeotic conversions of petals into sepals and stamens into carpels. Here, we describe the molecular characterization of seirena-1 (sei-1), a mutant from the basal eudicot California poppy (Eschscholzia californica) that shows homeotic changes characteristic of floral homeotic B class mutants. SEI has been previously described as EScaGLO, one of four B class-related MADS box genes in California poppy. The C terminus of SEI, including the highly conserved PI motif, is truncated in sei-1 proteins. Nevertheless, like the wild-type SEI protein, the sei-1 mutant protein is able to bind CArG-boxes and can form homodimers, heterodimers, and several higher order complexes with other MADS domain proteins. However, unlike the wild type, the mutant protein is not able to mediate higher order complexes consisting of specific B, C, and putative E class related proteins likely involved in specifying stamen identity. Within the PI motif, five highly conserved N-terminal amino acids are specifically required for this interaction. Several families lack this short conserved sequence, including the Brassicaceae, and we propose an evolutionary scenario to explain these functional differences.

Highlights

The regular appearance of the angiosperm flower requires distinct floral homeotic gene functions acting in a combinatorial manner
AP3/PI-like genes have been identified from many representatives of diverse angiosperm lineages, but mutant analyses have so far been performed only in core eudicots such as Arabidopsis, snapdragon (Antirrhinum majus), petunia (Petunia hybrida), and Medicago truncatula and the monocot grasses rice (Oryza sativa) and maize (Zea mays); mutants are generally affected in petal and stamen organ identity, or in lodicules, organs likely to be homologous to petals (Schwarz-Sommer et al, 1992; Tröbner et al, 1992; Angenent et al, 1995; Bowman et al, 1999; Ambrose et al, 2000; Nagasawa et al, 2003; Benlloch et al, 2009)
One PI/GLO gene has been identified in the California poppy genome, there are three known AP3/DEF paralogs, one of which is identified here

Summary

INTRODUCTION

The regular appearance of the angiosperm flower requires distinct floral homeotic gene functions acting in a combinatorial manner. The ABCE model of flower development explains how four different gene functions can specify organ identity of the four floral organ types. The action of the A function alone specifies the outer whorl sepals and has been found in Arabidopsis thaliana and close relatives. Concerted expression of class A and B governs petal organ identity; B and C function together to specify the stamens, and the C gene function alone is required for carpel identity. The E function acts throughout the flower and is required for the determination of all floral organs (Coen and Meyerowitz, 1991; Honma and Goto, 2001; Theissen and Saedler, 2001). The loss of the A, B, C, or E function leads to homeotic conversions of

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RESULTS

DISCUSSION

C Class Gene Regulation by B Class Genes

Findings

METHODS