ARABIDOPSIS LST8 proteins interact with target of rapamycin and over-expression of LST8 results in plants being hypersensitive to light
Lei Yao^1,2*, Jayanta Chatterjee², Gang Zeng¹, Hui Wang¹, Xiaohong Yan¹, Desh Pal S Verma²*

¹Beijing Agro-Biotechnology Research Center, Beijing Academy of Agriculture and Forestry Sciences, Beijing 100097, China.
²Department of Molecular Genetics and Plant Biotechnology Center, The Ohio State University, Columbus, Ohio 43210, USA.
* Corresponding Authors: yaolei@baafs.net.cn; verma.1@osu.edu

Abstract
LST8 (GβL) negatively regulates amino acid biosynthesis as a component of the TOR pathway in yeast. There are two homologs of LST8 in Arabidopsis, AtLST8.1 (At2g22040) and AtLST8.2 (At3g18140). Here we demonstrate that both AtLST8.1 and AtLST8.2 interact with TOR kinase. AtLST8.2 complements the function of yeast LST8, while AtLST8.1 does not. AtLST8.1 and AtLST8.2 have differential expression levels in plant development. AtLST8.1 only transcribed and expressed in inflorescence. Over expression of AtLST8.1 in wild type Arabidopsis down regulates the expression of AtLST8.2 and represses the primary bolting with increased branching. AtLST8.2 is an essential gene for plant development as three T-DNA insertion mutants showed that disruption of AtLST8.2 leads to embryo lethality. Constitutive expression of AtLST8.2 in wild type plants down regulates its own expression, and increases the expression of AtLST8.1, resulting in the plants that are hypersensitive to light intensity. The strong light halts the growth of AtLST8.2-transgenic plants. Fusion of GFP with AtLST8.2 and its expression revealed that AtLST8.2 is present in chloroplast. The PGK1, a glycolytic enzyme which is also expressed in chloroplast, reverses the response to AtLST8.2 expression level. These data suggest that AtLST8 proteins play an important role in photosynthesis and possibly amino acid metabolism in plants.

Key Words: LST8 proteins; TOR; hypersensitive; light; photosynthesis