Abstract
The fruit, which develops from the fertilised gynoecium formed in the innermost whorl of the flower, is the reproductive organ and one of the most complex structures of an angiosperm plant. Phytohormones play important roles during flower and fruit patterning, morphogenesis and growth, and there is emerging evidence for a cross-talk between different classes of plant hormones throughout these processes. Here, we show that the bHLH transcription factors HECATE 1 (HEC1), HEC2 and HEC3, which have previously been identified as essential components of transmitting tract formation, affect both auxin and cytokinin responses during reproductive tissue development. We find that HEC1 interacts with SPATULA (SPT) to control carpel fusion and that both transcription factors restrict sensitivity to cytokinin in the gynoecium. In addition, HEC1 is tightly integrated into the auxin-signalling network at the levels of biosynthesis, transport and transcriptional response. Based on this data, we propose that HEC1 acts as a local modulator of auxin and cytokinin responses to control gynoecium development in Arabidopsis.
Highlights
The flower is the defining structure of all angiosperms and has been studied in great detail in Arabidopsis
HECATE 1 (HEC1) and SPT act together during gynoecium development We have recently shown that HEC1 physically interacts with SPT in vivo to regulate stem cell proliferation in the shoot apical meristem (SAM) (Schuster et al, 2014)
HEC1 regulates auxin biosynthesis and transport in the gynoecium and fruit In a recent study, it was found that SPT and IND cooperate to locally modulate auxin signalling output by directly regulating the expression of PID (Girin et al, 2011)
Summary
The flower is the defining structure of all angiosperms and has been studied in great detail in Arabidopsis. It consists of four types of organs: The outer, leaf-like sepals and petals, and the gametophyteproducing stamens and carpels. Flower development begins with the specification of floral meristem identity in a subgroup of cells at the flank of the shoot apical meristem (SAM). Flower primordia emerge, become separated from the main stem cell system of the shoot apical meristem and floral organ primordia arise. The gynoecium is capped by specialised epidermal cells called stigmata that function in pollen reception and neighbour the cylindrical style, which connects the apical stigma with the large central ovary.
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