Light Stress and Photoprotection in Green algae, Mosses and Diatoms

The molecular bases of responses to light excess in photosynthetic organismshaving different evolutionary histories and belonging to different lineages are still not completely characterized.Therefore I explored the functions of photoprotective antennae in green algae, mosses and diatoms, together withthe role of the two xanthophyll cycles present in diatoms.I studied the Light Harvesting Complex Stress-Related (LHCSR) proteins in different organisms. In thegreen alga Chlamydomonas reinhardtii, LHCSR3 is a protein important for photoprotection. I used site-specificmutagenesis in vivo and in vitro and identified three residues of LHCSR3 that are responsible for its activation.With the moss Physcomitrella patens I studied the in vitro spectroscopic and quenching characteristics ofdifferent pigment-binding mutants of the protein LHCSR1, focusing in particular on chlorophylls A2 and A5.LHCSRs in diatoms are named LHCXs, and in Phaeodactylum tricornutum I found that multiple abioticstress signals converge to regulate the LHCX content of cells, providing a way to fine-tune light harvesting andphotoprotection.The other main driver of photoprotection in diatoms is the xanthophyll cycle. Here I found that the accu-mulation of viola- and zeaxanthin in P. tricornutum have a negative effect in the development of NPQ, showingthat zeaxanthin does not participate in the enhancing of NPQ in diatoms.Thanks to these studies done on different organisms, we gained a deeper knowledge on the shared character-istics and on the peculiar features about photoprotection in green algae, mosses and diatoms.