Differences in meristem size and expression of branching genes are associated with variation in panicle phenotype in wild and domesticated African rice

K N Ta,J Tregear,P Gantet,S Jouannic,T Harrop,A Ghesquière,Y M Staedler,N V Do,J Schönenberger,H Adam

doi:10.1186/s13227-017-0065-y

Abstract

BackgroundThe African rice Oryza glaberrima was domesticated from its wild relative Oryza barthii about 3000 years ago. During the domestication process, panicle complexity changed from a panicle with low complexity in O. barthii, to a highly branched panicle carrying more seeds in O. glaberrima. To understand the basis of this differential panicle development between the two species, we conducted morphological and molecular analyses of early panicle development.ResultsUsing X-ray tomography, we analyzed the morphological basis of early developmental stages of panicle development. We uncovered evidence for a wider rachis meristem in O. glaberrima than in O. barthii. At the molecular level, spatial and temporal expression profiles of orthologs of O. sativa genes related to meristem activity and meristem fate control were obtained using in situ hybridization and qRT-PCR. Despite highly conserved spatial expression patterns between O. glaberrima and O. barthii, differences in the expression levels of these early acting genes were detected.ConclusionThe higher complexity of the O. glaberrima panicle compared to that of its wild relative O. barthii is associated with a wider rachis meristem and a modification of expression of branching-related genes. Our study indicates that the expression of genes in the miR156/miR529/SPL and TAW1 pathways, along with that of their target genes, is altered from the unbranched stage of development. This suggests that differences in panicle complexity between the two African rice species result from early alterations to gene expression during reproductive development.

Highlights

The African rice Oryza glaberrima was domesticated from its wild relative Oryza barthii about 3000 years ago
It was shown recently that the miR156/miR529/SPL regulatory pathway, which plays a key role in the transition from the vegetative to the reproductive phase, is involved in the control of panicle complexity through the regulation of early acting genes such as LAX PANICLE1 (LAX1) and ABERRANT PANICLE ORGANIZATION2 (APO2), as well as the miR172/APETALA2 pathway and the SEPALLATA-like gene PAP2/OsMADS34 involved in spikelet and floret development [19]
We previously showed that the differential expression of male-gametogenesis-associated, miR2118-triggered, 21-nucleotide, phased siRNAs could be associated with the differential rate of spikelet development in panicles between O. glaberrima and O. barthii [20]

Summary

Introduction

The African rice Oryza glaberrima was domesticated from its wild relative Oryza barthii about 3000 years ago. It was shown recently that the miR156/miR529/SPL regulatory pathway, which plays a key role in the transition from the vegetative to the reproductive phase, is involved in the control of panicle complexity through the regulation of early acting genes such as LAX PANICLE1 (LAX1) and ABERRANT PANICLE ORGANIZATION2 (APO2), as well as the miR172/APETALA2 pathway and the SEPALLATA-like gene PAP2/OsMADS34 involved in spikelet and floret development [19]. Within this framework, it is important to determine to what extent these genes might be associated with panicle structure changes associated with rice domestication

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