The Analysis Of Expression Of Wee1 During The Development Of Rice Endosperm And Homology Of Wee1 Among Different Species

Endosperm is the main part of rice seed. The development of endosperm is closely related with the productive property of rice. At early developing stage of the endosperm, the more times of the mitosis proceed, the more the number of alveolus produce, which suggests the seed can develop larger volume of endosperm and form higher yield. Weel kinase is an important regulator to cell cycles and plays an important role in the development of endosperm. If weel gene expresses too early during the development of rice endosperm, wee1 kinase will restrain the effect of CDKs, and result in the endosperm cell division stopping at an early developing stage and carrying in endoreduplication—with only successive S phase (replication of DNA) without mitosis. Consequently, the cell number of endosperm will drop and correspondingly, the seed's capacity and strength for collecting storages will fall. On the contrary, If weel gene expresse and restrains the effect of the CDKs too late during endosperm development, it is likely that the endosperm has not enough time to complete cell enlargement and accumulate enough nutritive substance, which will also limit the increment of rice yield.In this research, expression of weel in the endosperm of Oryza sativa japonica cultivar Nipponbare, indica cultivar Yuexian18 and indica line 230027 was studied. Meanwhile, the functional domains and homology of weel kinases from different species were analyzed by using the methods of Bioinformatics. 1 The expressional difference of weel gene during endosperm development of three cultivars or line of rice. In japonica-cultivar Nipponbare, indica-cultivar Yuexian 18, and indica line 230027, the expression of weel gene can be detected in all of the investigated endosperm developmental phases (3 DAP～15 DAP), but the expression level of Weel is different among three rice cultivars or line. Nipponbare has smallest seeds, and the expression of Nipponbare Weel reaches the maximum at 4 DAP endosperm, indica-cultivar Yuexian 18 and indica line 230027 have long-shaped seeds, and the expression of their Weel reaches the maximum at 6 DAP and 8 DAP of endosperm respectively. Moreover, there still appears a secondary peak of Weel expression at 13 DAP endosperm, whether the expression of weel is related with the shape or not, this needs the further studies.2 Analysis of functional domains and homology of Weel kinases from different species.The amino acid sequences of Weel kinases from different species were aligned with CLUSTAL W 1.8. These species includedOryza sativa, Zea mays, Lycopersicon Mill, Arabidopsis thaliana, Glycine max, Mus musculus, Gallus gallus, Drosophila melanogaster, Rattus norvegicus, Danio rerio, Xenopus laevis, Strongylocentrotus purpuratus, Platynereis dumerilii, Saccharomyces cerevisiae etc. The results showed that all these Weel kinases have high homology and similarity in the functional domain, there exist a protein kinase ATP-binding region and an active site of Ser/Thr protein kinases in the Weel kinases from 16 species, and aspartic acid is necessary in the active-site of Ser/Thr protein kinases.By Neighbor-joining method of MEGA 3.1, a Phylogenetic tree was constructed based on the amino acid sequences of Weel kinases from 18 species. The results indicated that Weel kinases clustered based on the genetic distance among species. For example, Weel kinases from rice and maize clustered together, which suggested the genetic distance is short and a closer relationship exists between rice and maize. In dicotyledons, Weel kinases of Lycopersicon and Glycine clustered first, then up to that of Arabidopsis, which indicated the genetic distance between Lycopersicon and Glycine is shorter, and Arabidopsis is farther from the former two species in relationship. Similarly, Saccharomyces cerevisiae and Schizosaccharomyces pombe have a closer relationship, so their Weel kinases of them clustered together. The Phylogenetic tree suggested although Weel kinases among different species have high homology and similarity, there still exists significant boundary among species according to the genetic distance from each other. The evolution of Weel is coincident with "five boundary theory" proposed by Whittaker RH in 1969.