Os08g0191433

Annotated Information

Figure 1. BC12 Mutant VS. WT(from reference) .

Function

OsSSIIIa plays an important role in starch granule structures, amylose ratios and Physical and chemical properties of starch grains in the monocot plant rice. This gene OsIIIa is a second key enzyme of rice starch synthesisin.If OsSSIIIa gene encoding deletion or mutation , this will lead to changes in the grain starch -related traits.. It is also likely to be a good subject for exploring the link between cell growth and cell wall formation in rice.

Mutation

• Figure 1 shows the gross morphology of the wild type and mutant plants. The mutant was shorter than the wild type at the three-leaf and heading stages (Figures 1A and 1B). Also, mutant spikes and grains were slightly shorter than those of the wild type (Figure 1C). Nearly every internode of the mutant was shorter than that in the wild type.
  
  
• The breaking force of bc12 mutation culms and leaves was reduced to approximately 25% of that in the wild-type. The cellulose content was not significantly altered, but the lignin content was increased by approximately 50% in mutation. The higher lignin content resulted from a general increase in all three monomers..

Figure 2. Classification of the genes up- or downregulated fourfold or more in Mutation by whole-genome DNA microarray analysis

Expression

• Expression pattern of BC12
  Quantitative PCR revealed that BC12 is universally expressed in all organs examined, with higher expression in panicles and culms. The RT-PCR analyses also shows greater expression of BC12 in the tissues enriched in dividing cells than in those enriched in non-dividing cells.
  
  
• Expression Analysis in Mutant
  Affymetrix whole-genomemicroarray chip analyses by Juan Li et al. shows that 116 downregulated and 125 upregulated genes in the mutant compared with the wild type (more than four fold expression change; Figure 2). Of note, the genes involved in cell wall expansion were significantly altered in expression in the mutant.
  Those encoding xylanase inhibitor protein and cellulose synthase (CESA6) were greatly upregulated. By contrast, the gene for lignin forming anionic peroxidase was downregulated. That imply BC12 might be involved in the regulation of genes associated with cell wall assembly.Of note, the expression of the rice KO gene KO2, a key enzyme in early GA synthesis, was greatly decreased in mutation compared with the wild type.

Figure 3. Phylogenetic tree of BC12 and representative homologs from Arabidopsis and animals.(from reference) .

Localization

The production of OsSSIIIa was located at both the nucleus and cytoplasm and associated with microtubule arrays during cell division. An NLS with 17 amino acid sequence was found in this gene.

Evolution

Phylogenetic analysis by Mu Zhang et al. revealed that BC12 and motor proteins selected from various kinesin subfamilies are divided into separated clades(Figure 3). Kinesin-4 proteins from several representative species were clustered together but formed different subclades. Among the kinesin-4 proteins, those from rice and Arabidopsis were found to belong to a monophyletic clade with 100% bootstrap support. BC12 showed the closest homology to FRA1, which has been reported to be involved in cellulose microfibril deposition.

Knowledge Extension

• Gibberellins (GAs) are one of the most important endogenous growth regulators in plants. They are not only required for stem elongation but indeed participate in most stages of plant development. GAs mediate between certain environmental signals (e.g. light quality and photoperiod) and the inducedphysiological responses (e.g. stem extension and flowering). GA-deficient mutants are usually much shorter than the wild type, which indicates the corresponding genes such as sd1 (Os01g0883800) in rice may have a relationship with The Green revolution.

• The biosynthesis of GA in higher plants can be divided into three stages: (1) biosynthesis of ent-kaurene in proplastids;(2) conversion of ent-kaurene to GA12 via microsomal cytochrome P450 monooxygenases;(3) formation of C20- and C19-GAs in the cytoplasm. GA biosynthesis is catalyzed by three classes of enzymes: terpene cyclases catalyze the synthesis of ent-kaurene from geranylgeranyl diphosphate; cytochrome P450 monooxygenases catalyze the steps of the pathway from ent-kaurene to GA12; and soluble dioxygenases catalyze the final steps of the pathway.