Developmental regulation and significance of KNOX protein trafficking inArabidopsis

Abstract

Intercellular communication delivers critical informationfor position-dependent specification of cell fate. In plants, a novel mechanism for cell-to-cell communication involves the intercellular trafficking of regulatory proteins and mRNAs. The maize KNOTTED1 (KN1) gene acts non cellautonomously in the maize leaf, and KN1 was the first plant protein shown to traffic cell-to-cell, presumably through plasmodesmata. We have compared the intercellular trafficking of green fluorescent protein (GFP) fusions of KN1 and Arabidopsis KN1-related homeobox proteins to that of the viral movement protein from turnip vein clearing tobamovirus. We show that there is specific developmental regulation of GFP~KN1 trafficking. GFP~KN1 was able to traffic from the inner layers of the leaf to the epidermis, but not in the opposite direction, from epidermis to mesophyll. However, GFP or the GFP~movement protein fusion moved readily out of the epidermis. GFP~KN1 was however able to traffic out of the epidermal (L1) layer in the shoot apical meristem, indicating that KN1 movement out of the L1 was developmentally regulated. GFP~KNAT1/BREVIPEDICELLUS and GFP~SHOOT-MERISTEMLESS fusions could also traffic from the L1 to the L2/L3 layers of the meristem. In a test for the functional significance of trafficking, we showed that L1-specific expression of KN1 or of KNAT1 was able to partially complement the strong shootmeristemless-11 (stm-11) mutant. However, a cell-autonomous GUS fusion to KN1 showed neither trafficking ability nor complementation of stm-11 when expressed in the L1. These results suggest that the activity of KN1 and related homeobox proteins is maintained following intercellular trafficking, and that trafficking may be required for their normal developmental function.

Dual Effects of miR156-TargetedSPLGenes andCYP78A5/KLUHon Plastochron Length and Organ Size inArabidopsis thaliana

“…We chose the promoter of SHOOT MERISTEMLESS (STM) for the shoot apical meristem (Kim et al, 2003), that of FLOWERING LOCUS D (FD) for the shoot apical meristem and leaf anlagen (Abe et al, 2005;Wigge et al, 2005), that of LATERAL ORGAN BOUNDARIES (LOB) for the periphery of the shoot apical meristem (Shuai et al, 2002), those of AINTEGUMENTA (ANT) and ASYMMETRIC LEAVES1 (AS1) for young leaf primordia (Schoof et al, 2000;Eshed et al, 2001), that of the SCARECROW homolog BLS for late leaf primordia (Lifschitz et al, 2006), and that of the SUCROSE-PROTON SYMPORTER2 (SUC2) for vascular tissue (Truernit and Sauer, 1995;Imlau et al, 1999). Specific activity of the promoters, as reported in the literature, was confirmed by promoter b-glucuronidase (GUS) fusions (see Supplemental Figure 3 online).…”

Arabidopsis NPCC6/NaKR1 Is a Phloem Mobile Metal Binding Protein Necessary for Phloem Function and Root Meristem Maintenance

“…Trafficking of KN1 through PD requires an internal signal contained in the homeodomain (Kim et al, 2005), and the trafficking is essential for KN1 function in maintaining stem cell populations in plant shoots (Kim et al, 2003). NaKR1 shares no homology with the KN1 homeobox domain, and the presence of a signal sequence in NaKR1 remains to be tested.…”

The Fast and Transient Transcriptional Network of Gravity and Mechanical Stimulation in the Arabidopsis Root Apex

“…Expression studies of KNAT genes in different tissues were not able to detect expression in nonstimulated roots (Lincoln et al, 1994). KNAT1 is a non-cell-autonomous transcriptional activator and has been shown to be involved in shoot meristem cell fate determination (Chuck et al, 1996;Kim et al, 2003). After 30 min of gravity stimulation, but not after mechanical stimulation, the transcript levels of NO APICAL MERISTEM family (NAM) transcription factors were up-regulated as well.…”