Down-regulation of AUXIN RESPONSE FACTORS 6 and 8 by microRNA 167 leads to floral development defects and female sterility in tomato.

Ning Liu,Shan Wu,Biao Ding,Esther Van Der Knaap,Thomas H Clarke,Jason Van Houten,Ying Wang,Jason W Reed,Zhangjun Fei

doi:10.1093/jxb/eru141

Abstract

Auxin regulates the expression of diverse genes that affect plant growth and development. This regulation requires AUXIN RESPONSE FACTORS (ARFs) that bind to the promoter regions of these genes. ARF6 and ARF8 in Arabidopsis thaliana are required to promote inflorescence stem elongation and late stages of petal, stamen, and gynoecium development. All seed plants studied thus far have ARF6 and ARF8 orthologues as well as the microRNA miR167, which targets ARF6 and ARF8. Whether these genes have broadly conserved roles in flower development is not known. To address this question, the effects of down-regulation of ARF6 and ARF8 were investigated through transgenic expression of Arabidopsis MIR167a in tomato, which diverged from Arabidopsis before the radiation of dicotyledonous plants approximately 90-112 million years ago. The transgenic tomato plants overexpressing MIR167a exhibited reductions in leaf size and internode length as well as shortened petals, stamens, and styles. More significantly, the transgenic plants were female-sterile as a result of failure of wild-type pollen to germinate on the stigma surface and/or to grow through the style. RNA-Seq analysis identified many genes with significantly altered expression patterns, including those encoding products with functions in 'transcription regulation', 'cell wall' and 'lipid metabolism' categories. Putative orthologues of a subset of these genes were also differentially expressed in Arabidopsis arf6 arf8 mutant flowers. These results thus suggest that ARF6 and ARF8 have conserved roles in controlling growth and development of vegetative and flower organs in dicots.

Highlights

Various hormonal signals regulate flower and subsequent and Koltunow, 1999)
ARF6 and ARF8 orthologues are found in diverse angiosperms, including monocots and dicots (Remington et al, 2004), but their roles in plant development have only been tested in Arabidopsis (Nagpal et al, 2005; Reeves et al, 2012; Ru et al, 2006; Tabata et al, 2010)
The functions of the tomato ARF6 and ARF8 genes were evaluated by transgenically overexpressing the Arabidopsis MIR167a in this Solanaceous species

Summary

Introduction

Various hormonal signals regulate flower and subsequent and Koltunow, 1999). Among them, auxin is critical in fruit development (Kelley and Gasser, 2009; Nemhauser regulating gene expression within the flower and young et al, 1998; Nitsch, 1952; Serrani et al, 2008; Vivian-Smith fruit (Dharmasiri et al, 2005; Guilfoyle, 1986; Liscum and 2508 | Liu et al.Reed, 2002). Among Arabidopsis ARF proteins that mediate auxin-induced gene activation (Tiwari et al, 2003; Ulmasov et al, 1999a), ARF6 and ARF8 regulate growth in both vegetative and reproductive tissues. Arabidopsis arf arf flowers arrest as closed buds with short petals, short stamens, and indehiscent anthers, as well as defects in gynoecium growth and support of pollen tube growth (Nagpal et al, 2005). ARF6 and ARF8 promote jasmonic acid (JA) production, which in turn induces the expression of MYB21 and MYB24 required for petal, stamen, and gynoecium growth at anthesis (Reeves et al, 2012; Tabata et al, 2010). In Arabidopsis, ARF6 and ARF8 coordinate the development of petals and both male and female organs at the transition from closed buds to mature fertile flowers, which contributes to efficient fertilization

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Conclusion