Seedling morhpogenesis response to magnesium toxicity are modulated by the ABI1-DELLAs signaling pathway in Arabidopsis
Yuexi Cong¹, Yu Wang¹, Kunming Chen²*, Wanli Guo^1, * 

¹Institute of Crop Sciences, College of Agriculture and Biotechnology, Zhejiang University, 866 Yu-Hang-Tang Road, Hangzhou 310058, China.
²College of life Science, Northwest Agriculture and Forestry University, Yanglin, 712100, China.
*Corresponding Author：E-mail: gwl1016@yahoo.com.cn/wlguo@zju.edu.cn; kunmingchen@nwsuaf.edu.cn

Abstract
Magnesium (Mg²⁺) is an abundant divalent cation in a living cell and plays fundamental role in massive physiological and biochemical processes. However, the regulation mechanism in response to magnesium toxicity (MgT) in plant is known little so far. Here, these data elucidated that the characteristic seedling morphogensis MgT responses are at least in part dependent on the activity of the properties of ABA-mediated growth repressors DELLAs. The young leaves and roots are seriously inhibited and root hairs are induced more and longer under MgT and with exogenous application of ABA. Interestingly, the quadruple-DELLA mutant (Q) exhibited more than 1/3 times length of roots and root hairs, whereas, increased biomass, starch, chlorophyll and some metals contents in Q leaves and lower magnesium level was observed under MgT compared with wild types. However the phenotypes of Q under MgT can be eliminated by adding exogenous ABA indicate the ability of bioactive ABA is less increased in Q under MgT. Indeed, the roots of ABA insensitive abi1-1 mutant are resistant to the growth-inhibitory effects of both ABA and MgT, and both MgT and ABA promote the accumulation of a green fluorescent protein-tagged DELLA (GFP-RGA) in root cell nuclei. What's more, the transcription analysis using genes of ABA metabolism and signaling, magnesium transporters, and starch metabolism indicated that the remodeling of the young seedling in responding to MgT was regulated partly by DELLAs. In conclusion, these results suggested that ABI1-dependent ABA-mediated enhancement of DELLA restraint contributes to young seedling morphogenesis under MgT by systematic remodeling of stress signaling, transporters, and starch metabolism, etc.

Keywords: Magnesium toxicity, Seedling morphogenesis, DELLAs, ABA, abi1-1,  Arabidopsis