Os04g0396500

The rice gene Os03g0230500 was reported as LAX2 in 2011.

Annotated Information

Function

• LAX2 encodes a nuclear protein with a plant-specific conserved domain and that LAX2 physically interacts with LAX1 through a region containing this conserved domain. Thus, the rsearchers propose that LAX2 is a novel genetic component that is required for the process of AM formation and acts together with LAX1 in rice.

Mutation

• lax2 mutations were isolated while screening for mutants with abnormal panicle development. The researchers found three independent mutant alleles, all of which exhibited a sparse-panicle phenotype. These alleles, recovered from ethyl methanesulfonate, tissue culture, and g-ray irradiation mutagenesis populations, were designated as lax2-1, lax2-2, and lax2-3, respectively. To characterize the nature of the sparse appearance of the lax2-1 panicle, the researchers counted the number of inflorescence branches in the wild type and mutant. The lax2-1 mutant panicle produced fewer spikelets compared with the wild-type panicle (Figures 1A and 1E). Quantitative analysis of the lax2-1 mutant panicle revealed that the number of PBs was not affected in the mutant (Figure 1F). However, the number of total lateral branches, which was the sum of the number of PBs, SBs, and spikelets in a panicle, was reduced in lax2-1 (Figure 1G). This indicates that the sparse panicle appearance and the reduction in spikelet number in the lax2-1 mutant are attributable both to reduced higher order branching, such as the number of SBs, and to a reduced number of spikelets borne directly on branches (Figure 1B). Because a spikelet other than a terminal spikelet is produced as a lateral branch from an inflorescence meristem, lax2-1 mutants seem to have a defect in producing all the lateral branches other than PBs in panicles. lax2-1 mutants also had defects in vegetative development. In lax2-1 mutants, the number of tillers produced during vegetative growth was reduced (Figures 1C and 1H). Because there was no trace of tiller buds at the base of the leaves in lax2-1 mutants (Figure 1D), the reduction in the number of tillers is caused by a defect in AM formation and not by enhanced apical dominance or growth arrest of tiller buds. As a result of the reduction in the number of tillers in lax2-1, mature lax2-1 plants had fewer panicles than wild-type plants. Thus, the lax2-1 mutant failed to develop lateral branches during both vegetative and reproductive development, although the number of PBs in the panicle was not affected.

Figure 1. Plant Morphology of the lax2-1 Mutant. (A) Mature panicles. The lax2-1 mutant has a sparse appearance due to the production of fewer branches and spikelets. WT, wild type. (B) Enlarged view of boxes in (A). (C) Whole plants at the vegetative growth stage. lax2-1 mutant has fewer tillers than the wild type. (D) Culms of the wild type and lax2-1 after removal of the surrounding leaves. White arrowheads indicate the prophyll, which encloses the AM. (E) Quantification of the number of spikelets in a panicle. (F) Quantification of the number of PBs per panicle. (G) Quantification of the number of lateral branches, which is the sum of the number of PBs, SBs, and spikelets in a panicle. (H) Quantification of the number of tillers per plant. Error bars in (E) to (H) represent SD. The sample size for (E) to (H) is n = 9. .

• The other lax2 mutant alleles, lax2-2 and lax2-3, had similar branching defects, as observed in lax2-1 mutants in panicles, except that the number of PBs in lax2-2 and lax2-3 was slightly increased (Table 1).

Table 1. Phenotypic Characterization of lax2 Mutants and Their Respective Parental Wild Types in Rice .

• To clarify the genetic interactions of lax2 with other rice mutants that exhibit a defect in AM formation, the researchers made double mutants containing lax2 and either lax1 or moc1. lax1 had a sparse panicle with reduced SBs and spikelets, which was similar to the lax2 panicle, and lax1 had tillers with slightly reduced numbers at the vegetative stage (Figures 2A to 2C and 2G to 2I) (Oikawa and Kyozuka, 2009). The researchers made lax1 lax2 double mutants using null alleles of lax1, lax1-1, and lax1-6. lax1-1 is a deletion allele of lax1 (Komatsu et al., 2003), and lax1-6 has a single nucleotide deletion at the 59 end of the region encoding the conserved bHLH domain. The phenotype of the lax1 lax2 double mutant was more extreme than that of the single mutants.

Expression

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Evolution

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Labs working on this gene

• Crop Development Division, National Agriculture and Food Research Organization Agricultural Research Center, Niigata 943-0193, Japan
• National Center for Plant Gene Research, Key Laboratory of Molecular and Developmental Biology, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Beijing 100101, People’s Republic of China
• Department of Biological Mechanisms and Functions, Graduate School of Bioagricultural Sciences, Nagoya University, Nagoya 464-8601, Japan
• Photosynthesis and Photobiology Research Unit, National Institute of Agrobiological Sciences, Tsukuba 305-8602, Japan
• State Key Laboratory of Rice Biology, China National Rice Research Institute, Chinese Academy of Agricultural Sciences, Hangzhou 310006, People’s Republic of China
• Institute of Radiation Breeding, National Institute of Agrobiological Sciences, Hitachi-ohmiya 319-2293, Japan
• Bioscience and Biotechnology Center, Nagoya University, Nagoya 464-8601, Japan
• Rice Research Division, National Institute of Crop Science, National Agriculture and Food Research Organization, Tsukuba 305-8518, Japan
• Department of Agricultural and Environmental biology, Graduate School of Agricultural and Life Sciences, University of Tokyo, Tokyo 113-8657, Japan
• Precursory Research for Embryonic Science and Technology, Japan Science and Technology Agency, Kawaguchi 332-0012, Japan