3/15/2023 0 Comments Primordia torrent![]() ![]() Regions in colored dotted line boxes were imaged at enhanced resolution and are shown in corresponding boxes after denoising and contrast enhancement to highlight polar localization of AtPIN1-GFP in each cell (images without denoising and contrast enhancement are shown in Fig. The earliest primordium is marked as P 1 and the oldest incipient primordium is labeled as I 1. (A) View of vegetative tomato meristem stained by PI (red) from above showing a 3D volume rendering of pAtPIN1::AtPIN1-GFP expression and localization (green). Spatial distribution of PIN1 expression and polarity patterns, and effects of NPA and IAA on auxin gradient and PIN1 localization in early leaf primordia. (Scale bars: A and B, 20 μm C-J, 200 μm F and J Inset, 50 μm.) (G-J), Tomato leaf primordia after adaxial IAA microapplication, showing site of microapplication (G), early leaf (H), and more mature (I) primordia with strong defects in adaxial-abaxial polarity, and a transverse section through the midrib and adjacent laminal regions (J). Note that phloem cells (p) surround the xylem (x) elements. (C-F) Control tomato leaf primordia, showing schematic diagram of the meristem surface auxin flux direction (C), early primordium 4-5 d after emergence (D), 7 d after emergence (E), and a transverse section through the midrib and adjacent laminal regions with close-up insertion of vascular strand (F). S1 show DII-Venus signals in leaf primordia of additional stages. Stronger DII-Venus signals in the boundary and adjacent adaxial domain indicated weaker auxin signaling input. The abaxial domain in A has pFIL::DsRed-N7 (red) expression. DII-Venus signal is enriched in the adaxial domain from P 2 to P 9. DII-Venus signals are shown in green in A and B, and chlorophyll autofluorescence is in red (B). (A and B) Longitudinal and transverse sections through Arabidopsis SAM and leaf primordia region. Transient adaxial low auxin domain is important for leaf polarity patterning. Opposite to the original proposal, instead of a signal derived from the meristem, we show that a signaling molecule is departing from the primordium to the meristem to promote robustness in leaf patterning. Our results provide an explanation for the hypothetical meristem-derived leaf polarity signal. Furthermore, we show that auxin flow from emerging leaf primordia to the shoot apical meristem establishes the low auxin zone, and that this auxin flow contributes to leaf polarity. The auxin signal is mediated by the auxin-responsive transcription factor MONOPTEROS (MP), whose constitutive activation in the adaxial domain promotes abaxial cell fate. ![]() We also demonstrate that this adaxial low auxin domain contributes to leaf adaxial-abaxial patterning. Here we show the existence of a transient low auxin zone in the adaxial domain of early leaf primordia. It has long been proposed that the stem cells at the plant shoot apex produce a signal, which promotes leaf adaxial-abaxial (dorsoven-tral) patterning. Stem cells are responsible for organogenesis, but it is largely unknown whether and how information from stem cells acts to direct organ patterning after organ primordia are formed. ![]()
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