PLASTOCHRON1 , a timekeeper of leaf initiation in rice, encodes cytochrome P450

Abstract

During postembryonic development of higher plants, the shoot apical meristem produces lateral organs in a regular spacing (phyllotaxy) and a regular timing (plastochron). Molecular analysis of mutants associated with phyllotaxy and plastochron would greatly increase understanding of the developmental mechanism of plant architecture because phyllotaxy and plastochron are fundamental regulators of plant architecture. pla1 of rice is not only a plastochron mutant showing rapid leaf initiation without affecting phyllotaxy, but also a heterochronic mutant showing ectopic shoot formation in the reproductive phase. Thus, pla1 provides a tool for analyzing the molecular basis of temporal regulation in leaf development. In this work, we isolated the PLA1 gene by map-based cloning. The identified PLA1 gene encodes a cytochrome P450, CYP78A11, which potentially catalyzes substances controlling plant development. PLA1 is expressed in developing leaf primordia, bracts of the panicle, and elongating internodes, but not in the shoot apical meristem. The expression pattern and mutant phenotype suggest that the PLA1 gene acting in developing leaf primordia affects the timing of successive leaf initiation and the termination of vegetative growth.

LEAFY HEAD2, which encodes a putative RNA-binding protein, regulates shoot development of rice

“…Although molecular genetic and cell biology approaches have made significant advances in understanding the regulatory mechanism in leaf formation, most researches have been focused on phyllotaxy due to the lack of mutants that are exclusively defective in plastochron. The rice PLA1 gene is the first reported gene that is merely involved in regulating plastochron [17]. In view of the different performance between pla1 and lhd2 on tiller number and developmental phase transition, we assumed that LHD2 and PLA1 may regulate rice plant leaf initiation temporally in a distinct genetic pathway.…”

“…Isolation of genes regulating plastochron is of agronomical importance, because the number of leaves affects the number of tillers thus determines the number of panicles [17,24]. We here report the characterization of the rice mutant lhd2 and the molecular cloning of the LHD2 gene.…”

“…It is possible that the inhibition effect of preexisting primodia may not only determine the site of leaf initiation, but also prevent the precocious development of new leaves [7,16]. However, the analysis of the rice plastochron1 mutant that shows decreased plastochron with normal phyllotaxy provided the insight of the disassociation between regulatory pathway governing spatial and temporal patterns of the leaf initiation [12,17]. Molecular analysis revealed that PLA1 encodes CYP78A11, a member of cytochrome P450 family involved in phytohormone biosynthetic pathways [17].…”

“…However, the analysis of the rice plastochron1 mutant that shows decreased plastochron with normal phyllotaxy provided the insight of the disassociation between regulatory pathway governing spatial and temporal patterns of the leaf initiation [12,17]. Molecular analysis revealed that PLA1 encodes CYP78A11, a member of cytochrome P450 family involved in phytohormone biosynthetic pathways [17]. Either exogenous application of gibberellic acid (GA) or b RE refers to the restriction enzymes used in this study.…”

“…Either exogenous application of gibberellic acid (GA) or b RE refers to the restriction enzymes used in this study. [17][18][19]. An alternative mechanism that may regulate the timing and spacing of the leaf initiation comes from the identification of maize TERMINAL EAR1 (TE1), which encodes a putative RNA-binding protein [20].…”