A similar mechanism for plant protoplast regeneration and postembryo development：phosphoproteomic strategy in Physcomitrella patens
Xiaoqin Wang,^1,2 and Yikun He²*

¹Beijing University of Agriculture, Beijing 102206, China.
²College of Life Sciences, Capital Normal University, Beijing 100048, China.
^*Corresponding Author：Yikun He, College of Life Sciences, Capital Normal University, Beijing 100048, China; Telephone and Fax 86-10-68902203; E-mail, yhe@mail.cnu.edu.cn

Abstract
The moss Physcomitrella patens is an ideal model plant to study plant developmental processes. To better understand the mechanism of protoplast regeneration, we have carried out cellular and phosphoproteome analyses. Protonemal tissue was treated with driselase to produce protoplasts. After protoplasts regenerated for 4 d, we could observe cells dividing. Through a highly selective titanium dioxide (TiO2)-based phosphopeptide enrichment method and mass spectrometric technology, we identified more than 300 phosphoproteins as protoplast regeneration-responsive. Of these, 105 phosphoproteins were analyzed in detail. We found that a majority of the protoplast regeneration-responsive proteins were involved in regulations of postembryonic development and flower development, regulation of cell cycle, and specifications of floral organ identity and organ identity. These protein functions are related to postembryo development. The proteins in PPIs network are also related to postembryo development. Our study presents a comprehensive analysis of phosphoproteome involved in the network of protoplast regeneration and indicates that the mechanism of plant protoplast regeneration is similar to that of postembryo development.

Key Words: Protoplast regeneration, Phosphoproteome, Physcomitrella patens,   (TiO2)-enrichment, LC-MS/MS