Os04g0350700

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Annotated Information

The rice Os04g0350700 was reported as An-1 and analyzed by Chinese researchers in 2013.

Function

An-1 that encodes a basic helix-loop-helix (bHLH) protein and regulates the long-awn trait in wild rice.An-1 is intensely expressed at the apex of the lemma primordia, specifically causing continuous cell division to form a long awn. Upregulation of An-1 expression could induce long awns and grain elongation as well as reduce grain number per panicle in awnless cultivated rice.population genetic analysis of wild and cultivated rice showed a significant reduction in nucleotide diversity of the An-1 locus and revealed that the An-1 locus was a major target for artificial selection.

• An-1 Promotes Awn Development and Grain Length

Awn length in different plants(Figure 1).

figure.1 Awn Length Comparison

Grain length in different plants(Figure 2).

figure.2 Grain Length Comparison

• An-1 Negatively Regulates Grain Number per Panicle and,Thus, an-1 Increases Yield per Plant

Grain Number per Panicle and Yield per Plant Comparison(Figure 3).

figure.3 Grain Number per Panicle and Yield per Plant Comparison

Expression

• Expression pattern of An-1
  

During spikelet development, An-1 transcripts were first detected at the two rudimentary glume primordia and two empty glume primordia, next at the lemma and palea primordia, and then at the stamen and carpel primordia .An-1 expression increased gradually at the apices of lemma primordia.Then, An-1 expression strongly increased in awn primordia of Sp6, was maintained until Sp8e, and gradually faded during the Sp8l stage..

• An-1 expression level changes underlying the panicle phenotypes

qRT-PCR analysis showed that An-1 expression of young panicles was increased twofold in NIL-An-1(a near-isogenic line that contained only a 120-kb W1943 genomic fragment of the An-1 locus in GLA4 and exhibited a stable and similar awn length and awn rate) compared with that in GLA4 (Guangluai4). For complementary plants, An-1 expression increased nearly 40- to 45-fold in CPL-1(An-1 complementation plants) and CPL-2 plants compared with that in Nipponbare .In RNAi plants(An-1 suppression plants), the expression of endogenous An-1gene decreased. The extent of An-1 downregulation was highly correlated with panicle phenotypes in RNAi plants.The qRT-PCR results and panicle phenotypes suggested An-1 expression level was directly proportional to awn length and grain length but inversely proportional to grain number per panicle.qRT-PCR results and panicle phenotypes suggested An-1 expression level was directly proportional to awn length and grain length but inversely proportional to grain number per panicle.

Evolution

phylogenetic analysis of multiple An-1 sequences by Luo et al. 2013 showed that nearly all of the cultivars grouped together tightly, which revealed that these cultivars might have originated from a common progenitor in a single domestication event.(Figure 4.)

figure.4 Phylogenetic Tree of An-1 in Rice

Localization

The production of An-1 was located at the nucleus and functions as transcription factors with transactivation activity.A 1978-bp An-1 cDNA encodes a 262–amino acid protein containing a typical bHLH domain.

Knowledge Extension

O. sativa is divided into japonica and indica subspecies. Previous research showed that the domestication alleles of sh4, Prog1, qSW5, and Bh4 were fixed in both japonica and indica, while qSH1, Waxy, and Rc were fixed only in the japonica population.Awn is an extension of apex of the lemma of spikelet. As a characteristic of seeds in wild plants,long awns are reported to aid seed dispersal and seed burial and protect cereal grains from animal predation .In comparison to its wild progenitor, cultivated rice typically displays reduced seed shattering and dormancy, a reduction of outcrossing rate and awn length, erect growth, and pericarp and hull color conversion.

Labs working on this gene

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• National Center for Gene Research, Institute of Plant Physiology and Ecology, Shanghai Institutes for Biological Sciences, Chinese

Academy of Sciences, Shanghai 200233, China

• State Key Laboratory of Systematic and Evolutionary Botany, Key Laboratory of Plant Resources, Institute of Botany, Chinese

Academy of Sciences, Beijing 100093, China

• National Institute of Genetics, Mishima, Shizuoka 411-8540, Japan

References

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Kovach, M.J., Sweeney, M.T., and McCouch, S.R. (2007). New insights into the history of rice domestication. Trends Genet. 23:578–587.