PANICLE PHYTOMER2 (PAP2), encoding a SEPALLATA subfamily MADS-box protein, positively controls spikelet meristem identity in rice

In rice panicle development, new meristems are generated sequentially in an organized manner and acquire their identity in a time- and position-dependent manner. In the panicle of the panicle phytomer2-1 (pap2-1) mutant, the pattern of meristem initiation is disorganized and newly formed meristems show reduced competency to become spikelet meristems, resulting in the transformation of early arising spikelets into rachis branches. In addition, rudimentary glumes and sterile lemmas, the outermost organs of the spikelet, elongate into a leafy morphology. We propose that PAP2 is a positive regulator of spikelet meristem identity. Map-based cloning revealed that PAP2 encodes OsMADS34, a member of the SEPALLATA (SEP) subfamily of MADS-box proteins. PAP2/OsMADS34 belongs to the LOFSEP subgroup of MADS-box genes that show grass-specific diversification caused by gene duplication events. All five SEP subfamily genes in rice are expressed exclusively during panicle development, while their spatial and temporal expression patterns vary. PAP2 expression starts the earliest among the five SEP genes, and a low but significant level of PAP2 mRNA was detected in the inflorescence meristem, in branch meristems immediately after the transition, and in glume primordia, consistent with its role in the early development of spikelet formation. Our study provides new evidence supporting the hypothesis that the genes of the LOFSEP subgroup control developmental processes that are unique to grass species

The Naming of Names: Guidelines for Gene Nomenclature in Marchantia.

While Marchantia polymorpha has been utilized as a model system to investigate fundamental biological questions for over almost two centuries, there is renewed interest in M. polymorpha as a model genetic organism in the genomics era. Here we outline community guidelines for M. polymorpha gene and transgene nomenclature, and we anticipate that these guidelines will promote consistency and reduce both redundancy and confusion in the scientific literature

Insights into Land Plant Evolution Garnered from the Marchantia polymorpha Genome.

The evolution of land flora transformed the terrestrial environment. Land plants evolved from an ancestral charophycean alga from which they inherited developmental, biochemical, and cell biological attributes. Additional biochemical and physiological adaptations to land, and a life cycle with an alternation between multicellular haploid and diploid generations that facilitated efficient dispersal of desiccation tolerant spores, evolved in the ancestral land plant. We analyzed the genome of the liverwort Marchantia polymorpha, a member of a basal land plant lineage. Relative to charophycean algae, land plant genomes are characterized by genes encoding novel biochemical pathways, new phytohormone signaling pathways (notably auxin), expanded repertoires of signaling pathways, and increased diversity in some transcription factor families. Compared with other sequenced land plants, M. polymorpha exhibits low genetic redundancy in most regulatory pathways, with this portion of its genome resembling that predicted for the ancestral land plant. PAPERCLIP

New genes in the strigolactone-related shoot branching pathway

Shoot branching is controlled by the formation and subsequent outgrowth of axillary buds in the axils of leaves Axillary buds are indeterminate structures that can be arrested and await endogenous or environmental cues for outgrowth. A major breakthrough in this area of plant development has been the discovery that a specific group of terpenoid lactones, named strigolactones, can directly or indirectly, inhibit axillary bud outgrowth. Since that discovery, new branching mutants have been identified with reduced strigolactone levels or which are defective in strigolactone regulation or response. DWARF27 and DWARF14 probably act on strigolactone biosynthesis and strigolactone metabolism or signal transduction, respectively Auxin signaling mutants have also been useful in demonstrating that strigolactone levels are mediated by a classical auxin signal transduction pathway. The discovery and characterization of these mutants is an important first step toward understanding the mechanisms of strigolactone biosynthesis and signaling and their importance in regulating shoot branching. Crown Copyright © 2009

Two-Step Regulation and Continuous Retrotransposition of the Rice LINE-Type Retrotransposon Karma

Here, we report the identification of Karma, a LINE-type retrotransposon of plants for which continuous retrotransposition was observed in consecutive generations. The transcription of Karma is activated in cultured cells of rice upon DNA hypomethylation. However, transcription is insufficient for retrotransposition, because no increase in the copy number was observed in cultured cells or in the first generation of plants regenerated from them. Despite that finding, copy number increase was detected in the next generation of regenerated plants as well as in later generations, suggesting that the post-transcriptional regulation of Karma retrotransposition is development dependent. Our results indicate that two different mechanisms, one transcriptional and the other developmental, control the mobilization of Karma. In addition, unlike other known active plant retrotransposons, Karma is not subject to de novo methylation, and retrotransposition persists through several generations

Effects of genes increasing the number of spikelets per panicle, TAW1 and APO1, on yield and yield-related traits in rice

The genes TAWAWA1 (TAW1) and ABERRANT PANICLE ORGANIZATION1 (APO1) increase the number of spikelets per panicle (SN). In the present study, we examined the effects of these genes on morphological traits, yield, and yield-related traits including yield components using the near-isogenic lines (NILs) in the genetic background of a japonica rice variety, Koshihikari – NIL-taw1, NIL-apo1-D3, and NIL-apo1-D4 – in a field experiment. The SN and total number of spikelets per area of the three NILs were larger than those of Koshihikari. However, the yield of the three NILs did not exceed that of Koshihikari due to their low filling ability. Interestingly, our field experiments indicated that TAW1 did not affect the diameter of internodes and the PN, whereas APO1 decreased the PN and increased the diameter of internodes. These results suggest that TAW1 and APO1 differently affect yield-related traits