Proteomic Analysis Points to a Role for RAD23 in Apical Dominance in Pinus sylvestris var. Mongolica

In higher plants, apical dominance is the phenomenon whereby the main central stem is dominant over other side stems. In the present study, the natural loss of apical dominance in a Pinus sylvestris var. mongolica mutant was characterized. The mutant lacked an obvious trunk, but exhibited a large number of side stems, short internodes and leaves, and dwarfism. Cell biological analyses indicated that the meristem was changed dramatically in the mutant, with irregular cell arrangements, and no obvious layers of meristem and mature tissue. The loss of apical dominance in the mutant plant was accompanied by a significant decrease in auxin (A) and cytokinin (C) content compared to wild type, and increased C/A values. Proteomic analysis of the apical buds using 2DE-ESI-MS/MS at different stages of development (including dormancy, bud break, 10 days after bud break, and 15 days after bud break) revealed 49 proteins that were significantly changed in abundance compared to wild type. These proteins were involved in stress response, energy production and conversion, post-translation modification and amino acid transport and metabolism, as well as many other complex biological processes. Among the identified proteins, Rad23, an abscisic acid- and stress-induced protein, and cytoplasmic aconitate hydratase likely participate in ABA responses, Fe2+ ion homeostasis and the ubiquitin/26S proteasome pathway to regulate apical dominance of buds. Rad23, in particular, appears likely to play an important role in the complicated mechanism of apical dominance of Pinus sylvestris var. mongolica. This work provides important insights into this process as well as forming a basis for the further study of plant apical dominance.