The ASYMMETRIC LEAVES2 (AS2) gene of Arabidopsis thaliana is involved in the establishment of the leaf venation system, which includes the prominent midvein, as well as in the development of a symmetric lamina. The gene product also represses the expression of class 1 knox homeobox genes in leaves. We have characterized the AS2 gene, which appears to encode a novel protein with cysteine repeats (designated the C-motif) and a leucine-zipper-like sequence in the amino-terminal half of the primary sequence. The Arabidopsis genome contains 42 putative genes that potentially encode proteins with conserved amino acid sequences that include the C-motif and the leucine-zipper-like sequence in the amino-terminal half. Thus, the AS2 protein belongs to a novel family of proteins that we have designated the AS2 family. Members of this family except AS2 also have been designated ASLs (AS2-like proteins). Transcripts of AS2 were detected mainly in adaxial domains of cotyledonary primordia. Green fluorescent protein-fused AS2 was concentrated in plant cell nuclei. Overexpression of AS2 cDNA in transgenic Arabidopsis plants resulted in upwardly curled leaves, which differed markedly from the downwardly curled leaves generated by loss-of-function mutation of AS2. Our results suggest that AS2 functions in the transcription of a certain gene(s) in plant nuclei and thereby controls the formation of a symmetric flat leaf lamina and the establishment of a prominent midvein and other patterns of venation.
SummaryThe epidermis of higher plants generates the cuticle layer that covers the outer surface of each plant. The cuticle plays a crucial role in plant development, and some mutants with defective cuticle exhibit morphological abnormalities, such as the fusion of organs. The way in which the cuticle forms and its contribution to morphogenesis are poorly understood. Conventional detection of the cuticle by transmission electron microscopy (TEM) requires laborious procedures, which include ®xation, staining with osmium, and preparation of ultra-thin sections. It is also dif®cult to survey entire surfaces of expanded leaves because of the limited size of specimens that can be examined. Thus, TEM is unsuitable for large-scale screening for mutants with defective cuticle. We describe here a rapid and inexpensive method, designated the toluidine-blue (TB) test, for detection of cuticular defects in whole leaves. We demonstrated the validity of the TB test using mutants of Arabidopsis thaliana, including abnormal leaf shape1 (ale1), ®ddlehead (fdh), and ®ve eceriferum (cer) mutants, in which the structure and/or function of the cuticle is abnormal. Genetic screening for mutants using the TB test allowed us to identify seven loci. The cuticle-defective regions of leaves of the mutants revealed ®ve intrinsic patterns of surface defects (classes I through V), suggesting that formation of functional cuticle on leaves involves various spatially regulated factors.
SummaryAn NADPH oxidase analogous to that in mammalian phagocytes has been hypothesized to produce reactive oxygen species (ROS) in the plant defence response. A. thaliana contains at least six gp91 phox homologues, designated AtrbohA-F (A. thaliana Respiratory Burst Oxidase Homologues), which map to different positions. Transcripts of three of these genes can be detected in healthy plants by RNA gel blot analyses. The Atrboh gene products are closely related to gp91 phox and the intron locations suggest a common evolutionary origin. A putative EF-hand Ca 2⍣ -binding motif in the extended N-terminal region of the Atrboh proteins suggests a direct regulatory effect of Ca 2⍣ on the activity of the NADPH oxidase in plants.
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