Blue and red light upregulate α-expansin 1 (EXPA1) in transgenic Brassica rapa and its overexpression promotes leaf and root growth in Arabidopsis

Abstract

Light quality and the cell-growth-related proteins called expansins (EXPs) are two crucial factors in plant growth and development. However, molecular insights into the light responses of EXPs and the influences of light-dependent EXP expression changes on plant growth and development remain scarce. A preliminary analysis using a cDNA microarray revealed that red, blue, violet, and far-red light emitting diode (LED) light exposure and dark periods differentially regulate the expression of 27 Brassica rapa EXPs (BrEXPs). The results indicated that photosynthetically significant red and blue light induce the expression of BrEXPA1, and these results were further confirmed using a semi-qRT-PCR assay. The identification of several light-responsive cis-regulatory elements in the BrEXP promoter sequences suggested that light signals were perceived through these promoter motifs to regulate the gene expression that eventually controls growth and development. To substantiate our hypothesis that the light-dependent regulation of EXPs modulates growth and development, we developed transgenic reporter lines of B. rapa expressing GUS under the BrEXPA1 promoter. A histochemical analysis showed that BrEXPA1-promoter-driven GUS activity was prominent in the leaves, radicles, lateral roots, and flowers of plants grown under monochromatic red or blue light. The biological functions of BrEXPA1 were further tested by overexpressing sense (OE-S) and antisense BrEXPA1 (OE-AS) transcripts in Arabidopsis. The OE-S lines displayed long radicles, wide leaves, and additional rosette leaves compared to the controls, whereas the OE-AS lines exhibited early bolting. Collectively, our results demonstrated the relationship between light and BrEXPs and also the light-dependent role of BrEXPA1 in growth regulation.