OsRAMOSA2 Shapes Panicle Architecture through Regulating Pedicel Length.

Huan Lu,Ling Li,Zhengyan Dai,Xuexia Miao,Jiang Wang,Zhenying Shi

doi:10.3389/fpls.2017.01538

Abstract

The panicle architecture of rice is an important characteristic that influences reproductive success and yield. It is largely determined by the number and length of the primary and secondary branches. The number of panicle branches is defined by the inflorescence meristem state between determinacy and indeterminacy; for example, the maize ramosa2 (ra2) mutant has more branches in its tassel through loss of spikelet determinacy. Some genes and factors influencing the number of primary and secondary branches have been studied, but little is known about the molecular mechanism underlying pedicel development, which also influences panicle architecture. We report here that rice OsRAMOSA2 (OsRA2) gene modifies panicle architecture through regulating pedicel length. Ectopic expression of OsRA2 resulted in a shortened pedicel while inhibition of OsRA2 through RNA interference produced elongated pedicel. In addition, OsRA2 influenced seed morphology. The OsRA2 protein localized to the nucleus and showed transcriptional activation in yeast; in accordance with its function in pedicel development, OsRA2 mRNA was enriched in the anlagen of axillary meristems, such as primary and secondary branch meristems and the spikelet meristems of young panicles. This indicates a conserved role of OsRA2 for shaping the initial steps of inflorescence architecture. Genetic analysis revealed that OsRA2 may control panicle architecture using the same pathway as that of the axillary meristem gene LAX1 (LAX PANICLE1). Moreover, OsRA2 acted downstream of RCN2 in regulating pedicel and branch lengths, but upstream of RCN2 for control of the number of secondary branches, indicating that branch number and length development in the panicle were respectively regulated using parallel pathway. Functional conservation between OsRA2 and AtLOB, and the conservation and diversification of RA2 in maize and rice are also discussed.

Highlights

Rice (Oryza sativa L.) provides a staple food for more than half of the world’s population and a model plant for the molecular study of cereal crops
The LOB domain is characteristic of the Lateral Organ Boundaries Domain (LBD) family proteins (Bortiri et al, 2006), and in OsRA2 consists of a C block that functions in DNA-binding, a leucine zipper coiled coil motif for protein dimerization, and a Gly-Ala-Ser block (Figure 1B)
The C block is represented by a CX2CX6CX3C motif containing four conserved cysteine (C) residues and other non-conserved residues (X), and the leucine-zipper-like motif includes five hydrophobic amino acids separated by six variable amino acid residues (Shuai et al, 2002; Matsumura et al, 2009; Majer and Hochholdinger, 2011)

Summary

Introduction

Rice (Oryza sativa L.) provides a staple food for more than half of the world’s population and a model plant for the molecular study of cereal crops. The panicle architecture of cereal plants is mainly determined by the number and length of primary branches (PBs) and secondary branches (SBs) These are largely established by iterations of branching that are governed by spatiotemporal developmental decisions in inflorescence, branch and spikelet meristems between the maintenance of determinacy and indeterminacy (Kellogg et al, 2013; Teo et al, 2014; Zhang and Yuan, 2014). RCN1 and RCN2, rice homologs of TFL/CEN, lead to an indeterminate inflorescence and a more branched panicle when ectopically expressed (Nakagawa et al, 2002) These indeterminacy promoting and inhibiting factors interact with each other, for instance, CEN interacts with FLO in regulating inflorescence architecture (Bradley et al, 1996, 1997). It is not known if OsRA2 interact with other genes in panicle development?

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Results

Conclusion