Regulation of Expression Represents the Difference Between Direct and Indirect Shoot Regeneration.

Somatic cells of higher plants possess the remarkable ability to regenerate new individuals via reestablishing apical meristems. Reconstitution of shoot meristem is the vital process and is required for application of plant biotechnology. Under culture condition, shoot meristem can be formed directly or indirectly, depending on the absence or presence of callus as the intermediate status. However, the difference of regulatory mechanisms between the two regeneration types remains unknown. In this study, we established a bi-directional system in which shoots regenerated directly from lateral root primordia (LRP) and indirectly from hypocotyl-derived callus simultaneously. The results based on this system revealed that regulation of expression represents the difference between the two regeneration types in two aspects. Firstly, number of founder cells expressing is tightly associated with regeneration types. Relatively more founder cells gave rise to callus and produce larger meristem, whereas less founder cells produce LRP that regenerate smaller meristem. Secondly, non-CG DNA methylation specifically regulated transcription in LRP and promoted direct shoot regeneration, but had no influence on indirect regeneration. The results provide new insights for understanding the regulatory mechanisms of cell fate transition during organogenesis.