Functional Analysis Of AtNIN1, A Neutral Invertase, In Regulation Of Lateral Root Development

Sucrose cleavage plays a vital role in the plant growth and development for the allocation of crutial carbon resource and for the initiation of hexose-based sugar signals. Sucrose cleavage in plants possesses two pathways: one is mediated by invertases and another by synthases. Most plant cells have Acid invertases and Neutral/Alkaline invertases. Acid invertases are involved in the response to wounding and infection, cell differentiation and fruit development. The knowledge about Neutral/Alkaline invertases, however, is still limited.Osmotic stress inhibits lateral root development by repressing meristem activation. ABA is involved in this process. But detailed mechanism underlying osmotic induced lateral root inhibiton is unknown so far. We isolated an Arabidopsis mutant insensitive to osmotic stress in term of lateral root growth. Map-based cloning results showed that a gene for neutral invertase was point-mutated; therefore the mutant is named as Atninl. Physiological and molecular characterizations of Atninl mutant give the following conclusions:1. The length of primary root of Atninl is shorter than wild type, and Atninl is less sensitive to 3% mannitol induced inhibition on lateral root growth than wild type. By analyzing transgenic wild type and Atninl mutant harboring CycB1-GUS respectively, we found that cell division activity of lateral root primordium and lateral root meristem zone in Atninl under osmotic stress conditions was increased.2. AtNIN1 is involved in the regulation of floral transition, leaves and siliques development. Atninl mutant showed early flowering, smaller leaves and siliques, and shorter stems.3. Map base cloning results showed that AtNIN1 gene encoding a neutral invertase, which was confirmed by complemented results.4. AtNIN1 catalyzes sucrose into glucose and fructose. Protein sequence of AtNIN1 is dinstince from that of acid invertases. Neutral/Alkaline invertases are unique to plants and photosynthetic bacteria.