Search

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.ydbio.2009.07.042 Byline: Ken-ichiro Hibara (a), Mari Obara (a), Emi Hayashida (a), Masashi Abe (a), Tsutomu Ishimaru (a), Hikaru Satoh (b), Jun-ichi Itoh (a), Yasuo Nagato (a) Keywords: ADAXIALIZED LEAF1 (ADL1); Phytocalpain; Adaxial-abaxial axis; Embryo development; Aleurone layer; Epidermis specification Abstract: The adaxial-abaxial axis in leaf primordia is thought to be established first and is necessary for the expansion of the leaf lamina along the mediolateral axis. To understand axis information in leaf development, we isolated the adaxialized leaf1 (adl1) mutant in rice, which forms abaxially rolled leaves. adl1 leaves are covered with bulliform-like cells, which are normally distributed only on the adaxial surface. An adl1 double mutant with the adaxially snowy leaf mutant, which has albino cells that specifically appear in the abaxial mesophyll tissue, indicated that adl1 leaves show adaxialization in both epidermal and mesophyll tissues. The expression of HD-ZIPIII genes in adl1 mutant increased in mature leaves, but not in the young primordia or the SAM. This indicated that ADL1 may not be directly involved in determining initial leaf polarity, but rather is associated with the maintenance of axis information. ADL1 encodes a plant-specific calpain-like cysteine proteinase orthologous to maize DEFECTIVE KERNEL1. Furthermore, we identified intermediate and strong alleles of the adl1 mutant that generate shootless embryos and globular-arrested embryos with aleurone layer loss, respectively. We propose that ADL1 plays an important role in pattern formation of the leaf and embryo by promoting proper epidermal development. Author Affiliation: (a) Graduate School of Agricultural and Life Sciences, University of Tokyo, Tokyo 113-8657, Japan (b) Institute of Genetic Resources, Faculty of Agriculture, Kyushu University, Fukuoka 812-8581, Japan Article History: Received 23 March 2009; Revised 9 July 2009; Accepted 20 July 2009

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.ydbio.2008.04.040 Byline: Masashi Abe (a), Hideaki Kuroshita (a), Masaaki Umeda (b), Jun-Ichi Itoh (a), Yasuo Nagato (a) Keywords: Flattened shoot meristem; Rice; Apical meristem; CAF-1; Cell cycle; Fasciata1 Abstract: We isolated flattened shoot meristem (fsm) mutants in rice that showed defective seedling growth and died in the vegetative phase. Since most fsm plants had flat and small shoot apical meristems (SAMs), we suggest that FSM is required for proper SAM maintenance. FSM encodes a putative ortholog of Arabidopsis FASCIATA1 (FAS1) that corresponds to the p150 subunit of chromatin assembly factor-1 (CAF-1). FSM is expressed patchily in tissues with actively dividing cells, suggesting a tight association of FSM with specific cell-cycle phases. Double-target in situ hybridization counterstained with cell-cycle marker genes revealed that FSM is expressed mainly in the G.sub.1 phase. In fsm, expressions of the two marker genes representing S- and G.sub.2- to M-phases were enhanced in SAM, despite a reduced number of cells in SAM, suggesting that S- and G.sub.2-phases are prolonged in fsm. In addition, developmental events in fsm leaves took place at the proper time, indicating that the temporal regulation of development occurs independently of the cell-cycle period. In contrast to the fasciated phenotype of Arabidopsis fas1, fsm showed size reduction of SAM. The opposite phenotypes between fsm and fas1 indicate that the SAM maintenance is regulated differently between rice and Arabidopsis. Author Affiliation: (a) Graduate School of Agricultural and Life Sciences, University of Tokyo, Tokyo 113-8657, Japan (b) Graduate School of Biological Sciences, Nara Institute of Science and Technology, Ikoma, Nara 630-0192, Japan Article History: Received 20 December 2007; Revised 24 April 2008; Accepted 30 April 2008

Author(s): Takashi Kurakawa [1, 4]; Nanae Ueda [2, 4]; Masahiko Maekawa [3]; Kaoru Kobayashi [1]; Mikiko Kojima [2]; Yasuo Nagato [1]; Hitoshi Sakakibara (corresponding author) [2]; Junko Kyozuka (corresponding author) [...]

We report a recessive mutation of rice, aberrant panicle organization 1 (apo1), which severely affects inflorescence architecture, floral organ identity, and leaf production rate. In the wild-type inflorescence, the main-axis meristem aborts after forming 10-12 primary branch primordia. However, in apo1, the main-axis meristem was converted to a spikelet meristem after producing a small number of branch primordia. In addition, the branch meristems in apo1 became spikelet meristems earlier than in wild type. Therefore, in the inflorescence, the apo1 mutation caused the precocious conversion of the meristem identity. In the apo1 flower, lodicules were increased at the expense of stamens, and carpels were formed indeterminately by the loss of meristem determinacy. Vegetative development is also affected in the apo1. Leaves were formed rapidly throughout the vegetative phase, indicating that APO1 is also involved in temporal regulation of leaf production. These phenotypes suggest that the APO1 plays an important role in the temporal regulation of both vegetative and reproductive development. Keywords: Rice; Aberrant panicle organization 1; Inflorescence; Organ identity; Meristem; Phyllotaxy; Plastochron

To characterize the SHL2 and SHL1 genes in detail, we analyzed three strains carrying weak alleles of SHL2, shl2-6, shl2-7, and shl2-8, and one weak allele of SHL1, shl1-3. In contrast to strong alleles, which result in lack of shoot meristem, strains bearing these weak alleles formed shoot meristem frequently during embryogenesis. In shl2-6 and shl2-7 mutants, the meristem was lost during seed development. Only the shl2-8 mutant could survive after germination, but it showed abnormal initiation pattern and morphology of leaves. In strains bearing the weak alleles, the shoot meristem was composed of a small number of indeterminate cells and ultimately converted into leaf primordium. The shl1-3 mutant showed phenotypes similar to those of shl2-8. Thus SHL2 and SHL1 are required for both initiation and maintenance of shoot meristem. In shl2 mutants, there was a positive correlation between the size of the expression domain of OSH1 representing the number of indeterminate cells, the frequency of shoot meristem initiation, and the duration of meristem survival. Thus the shoot meristem will not initiate in an 'all-or-nothing' fashion, but is formed in various degrees depending on the strength of the alleles. Double-mutant analyses indicate that SHL2 functions upstream of SHO to establish proper organization of the shoot meristem.