Ectopic expression of the leucine-rich repeat-domain of cell wall extensin gene NpLRX1 disturbs morphogenesis of leaf cells by its association with cell membranes in tobacco

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NpLRX1 (Nicotiana plumbaginifolia Leucine-Rich Repeat-Extensin 1) encodes a chimeric leucine-rich repeat (LRR)/extensin protein and is thought to regulate cell morphogenesis that is essential for plant tissue formation. We have reported that abnormal cell morphogenesis was observed in NpLRX1-RNAi-introduced tobacco adventitious buds. A similar phenotype was observed when truncated NpLRX1 (N/LRR), a short N-terminal domain with LRR-domain, was expressed. Large gaps were observed between the cells with abnormal cell shapes in the leaves of the transgenic adventitious buds. The epidermal cells and the cuticle layer were defective in these leaves. The cells frequently swelled and the direction of cell division was sometimes out of order with an abnormal arrangement of microtubules in N/LRR-introduced tobacco BY-2 cultured cells. NpLRX1-GFP fusion proteins were detected on the cell membrane and in cell membrane-derived endocytic vesicles with partial degradation. These results suggest that ectopic expression of N/LRR causes defects in cell morphogenesis of tobacco tissues by the association of the LRR-domain with cell membrane.