Abstract
The phytohormone auxin is involved in many aspects of plant growth and developmental processes. The tomato Aux/IAA transcription factor SlIAA9/ENTIRE/E plays an important role in leaf morphogenesis and fruit development, and the E gene encodes a protein from the Aux/IAA family of auxin response repressors. Both SlIAA9-RNAi transgenic and entire (e) mutant plants reduce the leaf complexity in tomato, but the underlying mechanism is not yet completely resolved. Auxin signaling is known to regulate target genes expression via Aux/IAA and ARFs (auxin response factors) transcriptional regulators. ARFs mediate a wide range of developmental processes. Through an Y2H (yeast two-hybrid) assay coupled with expression profiling of the SlARF genes family, we identified a group of ARFs: SlARF6A, SlARF8A, SlARF8B, and SlARF24. Pull-down and BiFC (Bimolecular Fluorescence Complementation) results demonstrated that these SlARFs interact with SlIAA9 in vitro and in vivo, and the e mutation altered the expression patterns of multiple SlARFs. The simple leaves of the e mutant were partially converted to wild-type compound leaves by VIGS (virus-induced gene silencing) of these four SlARFs. Furthermore, IAA content in these samples was significantly increased compared to the e mutant. In addition, SlARF6A and SlARF24 bound to the SlPIN1 promoter and act as transcriptional activators to regulate genes expression involved in leaflet initiation. It may also suggest that SlARFs regulate leaf morphology through direct binding to auxin-responsive genes in the absence of SlIAA9, providing an insight for the role of SlARFs in leaf shape development.
Highlights
Leaves are one of the main organs of flowering plants, and exhibit a tremendous diversity in shape and size
To identify more SlARFs that may participate in this pathway, the full-length coding sequences of 15 SlARFs, including the candidate SlARF24 previously identified, were isolated and inserted into the yeast two hybrid vector pGADT7, including SlARF1, SlARF2B, SlARF3, SlARF4, SlARF5, SlARF6A, SlARF6B, SlARF8A, SlARF8B, SlARF9A, SlARF9B, SlARF10A, SlARF10B, and SlARF16A
We observed that yeast cells containing pGBKT7-SlIAA9 mated with pGADT7-SlARF6A, pGADT7-SlARF8A, pGADT7-SlARF8B, and pGADT7-SlARF24 respectively to grow under selection conditions (Figure 1A)
Summary
Leaves are one of the main organs of flowering plants, and exhibit a tremendous diversity in shape and size. The shape of leaves varies enormously within the same species and individual plants, and can be ascribed to ranging from simple to compound. Variation is one of the most conspicuous aspects of plant diversity in leaf shape. This diversity is often achieved by the adjustment of leaf. SlARFs Regulate Tomato Leaf Shapes blade dissection to form lobes or leaflets (Ben-Gera et al, 2012). Simple leaves comprise of a single continuous blade, whereas compound leaves are composed of multiple discontinuous blade units termed as leaflets (Koenig et al, 2009). Following the initiation of new shoot morphogenesis, leaves establish the basic framework for shape and size. The wild type leaves consist of primary, secondary, and intercalary leaflets with lobed margins in tomato (Berger et al, 2009)
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