Summary During embryogenesis, plants are thought to use a mechanism that allows the suspensor to maintain its identity. Here, we reported that RPL18a is involved in this mechanism in Arabidopsis thaliana. The suspensor cells proliferated in rp118aB and formed a multicellular structure rather than undergo pro- grammed cell death, as in wild type. Suspensors of rpl18a expressed the embryo proper marker, DRN：： GFP, but not the suspensor marker, WOX8：：GFP. In addition, auxin accumulated throughout the suspensors of rpl18a proembryos. Suspensor-specific expression of RPL18a could rescue the cell proliferation defects in rpl18a suspensors. These findings supported a role for RPL18a in maintaining suspensor identity.
The specific functions of the genes encoding arginine biosynthesis enzymes in plants are not well characterized. We report the isolation and characterization of Arabidopsis thaliana N-acetylglutamate kinase （NAGK）, which catalyzes the second step of arginine biosynthesis. NAGK is a plastid-localized protein and is expressed during most developmental processes in Arabidopsis. Heterologous expression of the Arabidopsis NAGK gene in a NAGK-deficient Escherichia coli strain fully restores bacterial growth on arginine-deficient medium, nagk mutant pollen tubes grow more slowly than wild type pollen tubes and the phenotype is restored by either specifically through complementation by NAGK in pollen, or exogenous supplementation of arginine, nagk female gametophytes are defective in micropylar pollen tube guidance due to the fact that female gametophyte cell fate specification was specifically affected. Expression of NAGK in synergid cells rescues the defect of nagk female gametophytes. Loss- of-function of NAGK results in Arabidopsis embryos not developing beyond the four-celled embryo stage. The embryo-defective phenotype in nagk/NAGK plants cannot be rescued by watering nagk/NAGK plants with arginine or ornithine supplementation. In conclusion, our results reveal a novel role of NAGK and arginine in regulating gametophyte function and embryo development, and provide valuable insights into arginine transport during embryo development.
Jie HuangDan ChenHailong YanFei XieYing YuLiyao ZhangMengxiang SunXiongbo Peng
Jojoba（Simmondsia chinensis） is mainly distributed in desert,and the molecular mechanisms of jojoba in response to abiotic stress still remain elusive.In this paper,we cloned and characterized a SOD gene from jojoba named as ScMnSOD,and introduced into Arabidopsis to investigate its functions of responding to drought stress.The transgenic Arabidopsis showed an improvement in drought tolerance.Moreover,under a water deficit condition,the accumulation of reactive oxygen species（ROS） was remarkably decreased in the transgenic lines compared to the WT.Furthermore,the ScMnSOD promoter was cloned to the 5′-upstream of GUS coding region in a binary vector,and introduced into Arabidopsis.And results showed that ScMnSOD expression can be induced by drought,salt,ABA,and low temperature.In conclusion,ScMnSOD plays an important role in drought tolerance which is,at least partially,attributed to its role in ROS detoxification.
