Evolution and functional diversification of the small Heat Shock Protein/α-Crystallin family in higher plants

HERNAN G BONDINO; ESTELA M. VALLE; ARJEN TEN HAVEN

PLANTA

SPRINGER

Lugar: Berlin; Año: 2012 vol. 235 p. 1299 - 1313

0032-0935

Small heat shock proteins (sHSPs) are chaperonesthat play an important role in stress tolerance. Theyconsist of an alpha-crystallin domain (ACD) Xanked byN- and C-terminal regions. However, not all proteins thatcontain an ACD, hereafter referred to as ACD proteins, aresHSPs because certain ACD proteins are known to havediVerent functions. Furthermore, since not all ACD proteinshave been identiWed yet, current classiWcations are incomplete.A total of 17 complete plant proteomes werescreened for the presence of ACD proteins by HMMERproWling and the identiWed ACD protein sequences wereclassiWed by maximum likelihood phylogeny. DiVerencesamong and within groups were analysed, and levels offunctional constraint were determined. There are 29 diVerentclasses of ACD proteins, eight of which contain classicalsHSPs and Wve likely chaperones. The other classescontain proteins with uncharacterised or poorly characterisedfunctions. N- and C-terminal sequences are conservedwithin the phylogenetic classes. Phylogenetics suggests asingle duplication of the CI sHSP ancestor that occurredprior to the speciation of mono- and dicotyledons. This wasfollowed by a number of more recent duplications thatresulted in the presence of many paralogues. The resultssuggest that N- and C-terminal sequences of sHSPs play arole in class-speciWc functionality and that non-sHSP ACDproteins have conserved but unexplored functions, whichare mainly determined by subsequences other than that ofthe ACD.