Chlorophyll is an essential pigment involved in light absorption and electron transfer in photosynthesis, a photochemical process that is indispensable for plant growth and development. The biosynthesis of chlorophyll occurs in plastids and shares a common biosynthetic pathway with other tetrapyrroles. The chlorophyll metabolic pathway is divided into four distinct components: the common pathway, chlorophyll-specific biosynthetic pathway, chlorophyll cycle, and chlorophyll degradation pathway, which are regulated in developmental- and environmental-specific manners. During the early stages of plant growth, the expression of most chlorophyll biosynthetic genes is induced by light, resulting in an increase in chlorophyll accumulation, induction of high photosynthetic activity, and continuous plant growth. In contrast, during plant maturation, the expression of most of these genes is gradually downregulated, whereas genes involved in chlorophyll degradation are upregulated during leaf senescence. Chlorophyll biosynthesis is directly or indirectly regulated by the members of various transcription factor families. In this review, we describe representative mechanisms of transcription factor-mediated activation and repression of chlorophyll biosynthesis in response to light treatment. We also present an overview of recent studies that have examined all the enzymatic steps involved in chlorophyll metabolic pathways and their gene regulation at the transcriptional level, which will enable readers to gain a better understanding of chlorophyll metabolism.

AbstractThe SHORT VEGETATIVE PHASE (SVP) gene encodes a MADS-box gene family of transcription factors that repress floral transition. To explore the function of the Brassica rapa SVP (BrSVP) gene during the flowering time of this species, a construct containing BrSVP under the control of the cauliflower mosaic virus 35S promoter was introduced into B. rapa via Agrobacterium-mediated transformation. The resulting transgenic plants showed delayed flowering time, and RT-PCR analyses further revealed that BrSVP repressed the expression of the floral integrator genes AGL20, AGL24, and FT during vernalization. Our data indicated that BrSVP acts as a negative regulator in the flowering time of B. rapa and that it may therefore be a useful genetic source for crop improvement with respect to flowering time regulation.

GROWTH-REGULATING FACTOR (GRF) genes encode plant-specific transcription factors and play critical roles in regulating the growth and development of lateral organs. In order to explore the agricultural potential of Brassica rapa GRF genes (BrGRFs), we constructed two BrGRF-overexpressing B. napus plants (BrGRF3-1OX and -9OX). BrGRF3-1OX and -9OX developed larger cotyledons, leaves, and seeds than the wild type. The increased organs’ sizes were due to increases in cell number, but not due to cell size alterations. RT-PCR analysis revealed that BrGRFs regulated the expression of a wide range of genes that are involved in gibberellin-, auxin-, cell division-related growth processes. Taken together, our data indicate that BrGRFs act as positive regulators of B. napus growth, thus raising the possibility that they may serve as a useful genetic source for crop improvement with respect to organ size and seed production.

APETALA2/ethylene response factor (AP2/ERF) transcription factors are involved in biological and abiotic stress response, plant development, and growth. AP2/ERF genes are classified into five families (AP2, DREB, ERF, RAV, and soloist), and most genes belong to DREB and ERF families. So far, genomic analysis of DREB and ERF family genes of various plant species has been performed, and classifications based on the homology of AP2/ERF-specific DNA binding domain, arrangement of exons and introns, and similarity of group-specific conserved motifs have been conducted. These classifications provide plausible information for the prediction of AP2/ERF gene function. In this paper, an overview of the classification, structure, evolution, and function of AP2/ERF genes is described, and the functional properties and regulatory mechanisms of ERF family genes that have been identified are summarized by group according to the functional classification of Arabidopsis ERF family genes. This shows that group-specific conserved motifs of Arabidopsis ERF family genes are closely linked with group-specific functions and regulatory mechanisms, indicating that the effective functional prediction of ERF family genes through such a classification scheme can be usefully applied to the trait improvements of various plants.