Expression of Three Putative Early Light-Induced Genes Under Different Stress Conditions in the Green Alga Ulva linza

Abstract

Ulva linza is a photophilous alga commonly distributed in shallow and horizontal habitats, and it is also a major contributor to biofouling. Early light-induced protein (ELIP) is a stress-related member of the light-harvesting complex family that is part of the photoprotective mechanism in land plants. In this study, we identified three ELIP-like genes in U. linza and analyzed their messenger RNA (mRNA) levels under different stress conditions. Expression of the ELIP-like1 and ELIP-like2 genes was light triggered, and the amount of ELIP-like2 transcripts increased in a light intensity-dependent manner. The mRNA levels of ELIP-like2 significantly increased, reached a maximum within 1 h after the transfer from low-intensity light to high-intensity light, and then rapidly returned to a low level. The amount of ELIP-like1 transcripts was maintained during the first 2 h after the transfer from low light to high light and then declined. The accumulation of ELIP-like1 and ELIP-like2 transcripts was also triggered by exposure to cold temperature and low osmotic stresses. In contrast, different light intensities had little effect on the response of the ELIP-like3 gene, and the transfer from low light to high light caused a decrease in the mRNA levels in a manner similar to that seen for major light-harvesting genes. Furthermore, none of the stress conditions tested resulted in up-regulation of the expression of ELIP-like3. These results suggest that ELIP-like1 and ELIP-like2 may participate in photoprotection in U. linza under high light, cold temperature, and low osmotic stress conditions. However, ELIP-like3 acted more like a structural component of the photosynthetic membranes.