OBP4 regulates cell proliferation-and-differentiation balance and pluripotent cell formation

Plant growth and development requires a continuous balance between cell division and differentiation. In root meristems, meristematic cells divide continuously to sustain root growth. Later, these cells differentiate, acquiring specialized functions, but losing their mitotic potential. Some plant cells types, such as pericycle cells, have a remarkable plasticity to be reprogrammed and to regenerate new organs and functional plants. However, the molecular mechanisms underlying cell reprogramming are not completely known.

In this work, a functional screening of transcription factors, using the Spanish collection TRANSPLANTA, identifies Arabidopsis OBP4 as a novel regulator of root growth by reducing cell elongation and cell differentiation. Overexpression of OBP4 regulates the levels of a large number of transcripts in roots; many of them involved in hormonal signaling and in the formation of callus, a mass of proliferative cells derived from reprogrammed pericycle cells. OBP4 does not induce cell division in the root meristem but it promotes pericycle cell proliferation, forming callus-likes structures at the root tip as shown by expression of stem cells markers. Callus formation is enhanced by ectopic expression of OBP4 in wild type or in alf4-1, while being significantly reduced in roots that have low levels of OBP4. Our data provide molecular insights into how differentiated root cells acquire the potential to generate callus, a pluripotent mass of cells that can regenerate fully functional organs and plants. These results might be relevant for improving in vitro plant regeneration and propagation of species with high biological and/or comercial value.