Identification of Small RNAs During High Light Acclimation in Arabidopsis thaliana

The biological significance of non-coding RNAs (ncRNAs) has been firmly established to be important for the regulation of genes involved in stress acclimation. Light plays an important role for the growth of plants providing the energy for photosynthesis; however, excessive light conditions can also cause substantial defects. Small RNAs (sRNAs) are a class of non-coding RNAs that regulate transcript levels of protein-coding genes and mediate epigenetic silencing. Next generation sequencing facilitates the identification of small non-coding RNA classes such as miRNAs (microRNAs) and small-interfering RNAs (siRNAs), and long non-coding RNAs (lncRNAs), but changes in the ncRNA transcriptome in response to high light are poorly understood. We subjected Arabidopsis plants to high light conditions and performed a temporal in-depth study of the transcriptome data after 3 h, 6 h, and 2 days of high light treatment. We identified a large number of high light responsive miRNAs and sRNAs derived from NAT gene pairs, lncRNAs and TAS transcripts. We performed target predictions for differentially expressed miRNAs and correlated their expression levels through mRNA sequencing data. GO analysis of the targets revealed an overrepresentation of genes involved in transcriptional regulation. In A. thaliana, sRNA-mediated regulation of gene expression in response to high light treatment is mainly carried out by miRNAs and sRNAs derived from NAT gene pairs, and from lncRNAs. This study provides a deeper understanding of sRNA-dependent regulatory networks in high light acclimation.

Effects of lincomycin on PSII efficiency, non-photochemical quenching, D1 protein and xanthophyll cycle during photoinhibition and recovery

Leaves of Parthenocissus quinquefolia (L.) Planch. (Virginia creeper) were treated with lincomycin (an inhibitor of chloroplast-encoded protein synthesis), subjected to a high-light treatment and allowed to recover in low light. While lincomycin-treated leaves had similar characteristics as controls after a 1 h exposure to high light, total D1 levels in lincomycin-treated leaves were half those in controls at the end of the recovery period. In addition, lincomycin delayed recovery of maximal PSII efficiency of open centers (ratio of variable to maximal chlorophyll fluorescence, F v / F m) and of estimated PSII photochemistry rate upon return to low light subsequent to the high-light treatment. Furthermore, lincomycin treatment slowed the removal of zeaxanthin (Z) and antheraxanthin (A) during recovery in low light, and the level of thermal energy dissipation (non-photochemical fluorescence quenching, NPQ) remained elevated. In lincomycin-treated leaves infiltrated with the uncoupler nigericin immediately after high-light exposure, thermal energy dissipation, sustained with lincomycin alone, declined quickly to control levels. In summary, lincomycin treatment affected not only D1 protein turnover but also xanthophyll-cycle operation and thermal-energy dissipation. The latter effect was apparently a result of the maintenance of a high trans-thylakoid proton gradient. Similar effects were also seen subsequent to short-term exposures to high light in lincomycin-treated Spinacia oleracea L. (spinach) leaves. In contrast, lincomycin treatments under low-light levels did not induce Z formation or NPQ. These results suggest that lincomycin has the potential to lower PSII efficiency (F v / F m) through inhibition of NPQ relaxation and Z + A removal subsequent to high-light exposures.