Barren inflorescence2Encodes a Co-Ortholog of thePINOIDSerine/Threonine Kinase and Is Required for Organogenesis during Inflorescence and Vegetative Development in Maize

Paula Mcsteen,Andrea Skirpan,China Lunde,Xianting Wu,Sarah Hake,Simon Malcomber,Elizabeth Kellogg

doi:10.1104/pp.107.098558

Abstract

Organogenesis in plants is controlled by meristems. Axillary meristems, which give rise to branches and flowers, play a critical role in plant architecture and reproduction. Maize (Zea mays) and rice (Oryza sativa) have additional types of axillary meristems in the inflorescence compared to Arabidopsis (Arabidopsis thaliana) and thus provide an excellent model system to study axillary meristem initiation. Previously, we characterized the barren inflorescence2 (bif2) mutant in maize and showed that bif2 plays a key role in axillary meristem and lateral primordia initiation in the inflorescence. In this article, we cloned bif2 by transposon tagging. Isolation of bif2-like genes from seven other grasses, along with phylogenetic analysis, showed that bif2 is a co-ortholog of PINOID (PID), which regulates auxin transport in Arabidopsis. Expression analysis showed that bif2 is expressed in all axillary meristems and lateral primordia during inflorescence and vegetative development in maize and rice. Further phenotypic analysis of bif2 mutants in maize illustrates additional roles of bif2 during vegetative development. We propose that bif2/PID sequence and expression are conserved between grasses and Arabidopsis, attesting to the important role they play in development. We provide further support that bif2, and by analogy PID, is required for initiation of both axillary meristems and lateral primordia.

Highlights

Organogenesis in plants is controlled by meristems
Axillary meristems, which arise in the axils of leaves, play an important role in organogenesis by producing branches and flowers
In Arabidopsis (Arabidopsis thaliana), pinformed1, pinoid, yucca, and monopteros mutants have similar phenotypes to auxin transport-inhibited plants forming a pin-shaped inflorescence with very few flowers (Okada et al, 1991; Bennett et al, 1995; Przemeck et al, 1996; Cheng et al, 2006)

Summary

Introduction

Organogenesis in plants is controlled by meristems. Axillary meristems, which give rise to branches and flowers, play a critical role in plant architecture and reproduction. Both maize (Zea mays) and rice (Oryza sativa) inflorescences are more branched than Arabidopsis due to the presence of additional axillary meristem types (Bonnett, 1948; Cheng et al, 1983; Clifford, 1987; Irish, 1997; McSteen et al, 2000; Shimamoto and Kyozuka, 2002). Mutants that fail to initiate branches, spikelets, and florets during inflorescence development have been used to identify genes that regulate axillary meristem initiation (Coe et al, 1988; Doebley et al, 1995; Komatsu et al, 2001, 2003a; McSteen and Hake, 2001; Ritter et al, 2002; Li et al, 2003; Gallavotti et al, 2004). Barren inflorescence (bif2) mutants make fewer ear shoots, branches, spikelets, florets, and floral organs, indicating that bif is required for axillary meristem and lateral organ initiation in the maize inflorescence (Fig. 1B; McSteen and Hake, 2001). The term co-ortholog (Sonnhammer and Koonin, 2002) is used rather than ortholog because multiple rounds of genome duplication have occurred in both monocot and eudicot lineages (Sonnhammer and Koonin, 2002; Bowers et al, 2003; Paterson et al, 2004; Yu et al, 2005)

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Conclusion