Description
During leaf development, the timing of transition from cell proliferation to
expansion is an important factor in determining the final organ size. However,
the regulatory system involved in this transition remains less understood. To get
an insight into this system, we investigated the compensation phenomenon, in
which the cell number decreases while the cell size increases in organs with
determinate growth. Compensation is observed in several plant species
suggesting coordination between cell proliferation and expansion. In this
study, we examined an Arabidopsis mutant of ANGUSTIFOLIA 3 (AN3)/GRF-
INTERACTING FACTOR 1, a positive regulator of cell proliferation, which exhibits
the compensation. Though the AN3 role has been extensively investigated, the
mechanism underlying excess cell expansion in the an3 mutant remains
unknown. Focusing on the early stage of leaf development, we performed
kinematic, cytological, biochemical, and transcriptome analyses, and found
that the cell size had already increased during the proliferation phase, with
active cell proliferation in the an3 mutant. Moreover, at this stage, chloroplasts,
vacuoles, and xylem cells developed earlier than in the wild-type cells.
Transcriptome data showed that photosynthetic activity and secondary cell
wall biosynthesis were activated in an3 proliferating cells. These results
indicated that precocious cell differentiation occurs in an3 cells. Therefore, we
suggest a novel AN3 role in the suppression of cell expansion/differentiation
during the cell proliferation phase.