SummaryShoots of higher plants exhibit negative gravitropism. However, little is known about the mechanism or site of gravity perception in shoots. We have identified two loci that are essential for normal shoot gravitropism in Arabidopsis thaliana. Genetic analysis demonstrated that the shoot gravitropism mutants sgr1 and sgr7 are allelic to the radial pattern mutants, scr and shr, respectively. Characterization of the aerial phenotype of these mutants revealed that the primary defect is the absence of a normal endodermis in hypocotyls and inflorescence stems. This indicates that the endodermis is essential for shoot gravitropism and strongly suggests that this cell layer functions as the gravity-sensing cell layer in dicotyledonous plant shoots. These results also demonstrate that, in addition to their previously characterized role in root radial patterning, SCR and SHR regulate the radial organization of the shoot axial organs in Arabidopsis.

In dicotyledonous plants, two cotyledons are formed at bilaterally symmetric positions in the apical region of the embryo. Single mutations in the PIN-FORMED1 (PIN1) and PINOID (PID)genes, which mediate auxin-dependent organ formation, moderately disrupt the symmetric patterning of cotyledons. We report that the pin1 piddouble mutant displays a striking phenotype that completely lacks cotyledons and bilateral symmetry. In the double mutant embryo, the expression domains of CUP-SHAPED COTYLEDON1 (CUC1), CUC2 and SHOOT MERISTEMLESS (STM), the functions of which are normally required to repress growth at cotyledon boundaries, expand to the periphery and overlap with a cotyledon-specific marker, FILAMENTOUS FLOWER. Elimination of CUC1, CUC2 or STM activity leads to recovery of cotyledon growth in the double mutant, suggesting that the negative regulation of these boundary genes by PIN1 and PID is sufficient for primordium growth. We also show that PID mRNA is localized mainly to the boundaries of cotyledon primordia and early expression of PID mRNA is dependent on PIN1. Our results demonstrate the redundant roles of PIN1 and PID in the establishment of bilateral symmetry, as well as in the promotion of cotyledon outgrowth, the latter of which involves the negative regulation of CUC1, CUC2 and STM genes, which are boundary-specific downstream effectors.

DNA barcoding is a technique for identifying organisms based on a short, standardized fragment of genomic DNA. The standardized sequence region is called a DNA barcode because it is like a barcode tag for each taxon. Since the proposition of this concept and the launch of a large project named the Barcode of Life, this simple technique has attracted attention from taxonomists, ecologists, conservation biologists, agriculturists, plant-quarantine officers and others, and the number of studies using the DNA barcode has rapidly increased. The extreme diversity of insects and their economical, epidemiological and agricultural importance have made this group a major target of DNA barcoding. However, there is some controversy about the utility of DNA barcoding. In this review, we present an overview of DNA barcoding and its application to entomology. We also introduce current advances and future implications of this promising technique.

In higher plants, the shoot and the root generally show negative and positive gravitropism, respectively. To elucidate the molecular mechanisms involved in gravitropism, we have isolated many shoot gravitropism mutants in Arabidopsis. The sgr2 and zig/sgr4 mutants exhibited abnormal gravitropism in both inflorescence stems and hypocotyls. These genes probably are involved in the early step(s) of the gravitropic response. The sgr2 mutants also had misshapen seed and seedlings, whereas the stem of the zig/sgr4 mutants elongated in a zigzag fashion. The SGR2 gene encodes a novel protein that may be part of a gene family represented by bovine phosphatidic acid-preferring phospholipase A1 containing a putative transmembrane domain. This gene family has been reported only in eukaryotes. The ZIG gene was found to encode AtVTI11, a protein that is homologous with yeast VTI1 and is involved in vesicle transport. Our observations suggest that the two genes may be involved in a vacuolar membrane system that affects shoot gravitropism. INTRODUCTIONPlants settle in their place of germination through their lifetime and cannot escape the various environmental stimuli to which they are exposed. Consequently, plants have evolved many mechanisms by which they can sense and adapt themselves to various environmental changes. Gravitropism is one of those important environmental responses, particularly for land plants. This is the response that the plant makes when it is laid flat on the ground, namely, the shoot curves up (negative gravitropism) and the root curves down (positive gravitropism). This response is necessary to position the plant so that its leaves face the source of light energy and its roots can take up water and various nutrients.A number of physiological and cytological studies using many different species of plants have demonstrated that amyloplasts that accumulate starch are involved in gravity perception as statoliths and that auxin is involved in the asymmetric growth between the upper and lower tissue of the responding organ that results in the gravitropic curvature (Sack, 1991; Kaufman et al., 1995). These studies also have suggested that various signal molecules, such as Ca 2 ϩ , calmodulin, and inositol 1,4,5-triphosphate, and pH change are involved in the signal transduction that generates the gravitropic response (Belyavskaya, 1996;Sinclair and Trewavas, 1997;Perera et al., 1999;Scott and Allen, 1999;Fasano et al., 2001).To elucidate the molecular mechanism of the gravitropic response in higher plants, many mutants with aberrant root or shoot gravitropism have been isolated from Arabidopsis (Firn et al., 2000;Tasaka et al., 2001). With respect to root or hypocotyl gravitropism, most of the mutants that are abnormal in this function also respond abnormally to auxin treatment. This suggests that a number of auxin-related genes are involved in this response. These include the AUX1 ( AUXIN RESISTANT 1 ) and EIR1/AGR1/PIN2 ( ETHYLENE INSENSITIVE ROOT 1/AGRAVITROPIC 1/PIN-FORMED 2 ) genes, which appear to be in...