The plastid-nucleus located DNA/RNA binding protein WHIRLY1 regulates microRNA-levels during stress

Abstract

In this article a novel mechanism of retrograde signaling by chloroplasts during stress is described. This mechanism involves the DNA/RNA binding protein WHIRLY1 as a regulator of microRNA levels. By virtue of its dual localization in chloroplasts and the nucleus of the same cell, WHIRLY1 was proposed as an excellent candidate coordinator of chloroplast function and nuclear gene expression (Grabowski et al., 2008; Foyer et al., 2014). In this study the putative involvement of WHIRLY1 in stress dependent retrograde signaling was investigated by comparison of barley (Hordeum vulgare L., cv. Golden Promise) wild-type and transgenic plants with an RNAi-mediated knockdown of WHIRLY1. In contrast to the wild type, the transgenic plants were unable to cope with continuous high light conditions. They were impaired in production of several microRNAs mediating post-transcriptional responses during stress (Kruszka et al., 2012, Sunkar et al., 2012). The results support a central role of WHIRLY1 in retrograde signaling and underpin a so far underestimated role of microRNAs in this process.