The barley mutant happy under the sun 1 (hus1): a further step towards a new generation of pale green crops.

Truncated antenna size of photosystems and lower leaf chlorophyll content has been shown to increase photosynthetic efficiency and biomass accumulation in microalgae, cyanobacteria and higher plants grown under high-density cultivation conditions. Here, we have asked whether this strategy is also applicable to a major crop by characterizing the barley mutant happy under the sun 1 (hus1). The pale green phenotype of hus1 is due to a 50% reduction in the chlorophyll content of leaves, owing to a premature stop codon in the HvcpSRP43 gene for the 43-kDa chloroplast Signal Recognition Particle (cpSRP43). The HvcpSRP43 protein is responsible for the uploading of photosystem antenna proteins into the thylakoid membranes, and its truncation results in a smaller photosystem antenna size. Besides a detailed molecular and physiological characterization of the mutant grown under controlled greenhouse conditions, we show that the agronomic performance of hus1 plants, in terms of total biomass production and grain yield under standard field conditions, is comparable to that of control plants. The results are discussed in terms of the potential benefits of the hus1 phenotype, and of natural allelic variants of the HvcpSRP43 locus, with respect to productivity and mitigation of climate change.

This project was supported by ERA-NET Cofund FACCE SURPLUS (BarPLUS grant id. 93) funded by MIUR to PP, by MIPAAF to AT and by FACCE SURPLUS/I/BARPLUS/05/2016 (funded by the National Center for Research and Development in Poland) to AJ. We are also grateful to MIUR-PRIN 2017FBS8YN to PP. The NoLimits platform at University of Milano is acknowledged for the TEM analysis. We are also grateful to Laurent Nussaume for providing us with the AtcpSRP43 antibody. This manuscript is dedicated to the memory of Prof. Michele Stanca, a world-renowned scientist, who transmitted his passion for cereal genetics to many of the scientists that co-authored this article. Paul Hardy is also acknowledged for critical reading of the manuscript.