Minisymposium 27: Temperature

Abs # 48002: Diversification of chloroplast small heat shock proteins in plants

Presenter:	Luthe, dawn S., dsluthe@ra.msstate.edu
Authors	Qureshi, Samina N. (A)   Heckathorn, Scott A. (B)   Luthe, dawn S. (A)
Affiliations:	(A): Mississippi State University (B): University of Toledo

It has been demonstrated that the chloroplast-localized, small heat shock proteins (Cp-sHSP) are correlated with increased thermotolerance in a number of plant species. They have been shown to improve heat tolerance by protecting Photosystem II during high temperature stress. We have demonstrated that the presence of an additional Cp-sHSP isoform in a heat tolerant variant of Agrostis stolonifera appears to protect proteins in the Oxygen Evolving Complex in PSII. Currently, our research is focused on determining the functional significance of qualitative and quantitative variation in Cp-sHSPs in plant species and ecotypes with differing levels of heat tolerance. To accomplish this, we are isolating and characterizing the Cp-sHSP genes from heat-sensitive species, A. stononifera, Chenopodium album (New York and Mississippi ecotypes), moderately heat-tolerant species, Spartina alternifloraand Amaranthus retroflexus, and very heat-tolerant species, Agave americana and Ferocactus wislizenii. Gene-specific primers were designed from the methionine-rich (met-rich) and Consensus I regions of the Cp-sHSP that directed the amplification of 300 to 400 bp fragments. These fragments have been cloned and sequenced and are being used for PCR-based genome walking so that complete genes can be isolated. The amino acid sequences derived from these fragments were aligned with Cp-sHSP from other monocot and dicot species. Although the New York (Chenopodium-NY) and Mississippi (Chenopodium-MS) ecotypes of C. album were 97% similar and 94% identical in the met-rich region, there was far less similarity carboxyl-terminal region. Phylogenetic analysis showed that the Cp-sHSP from Chenopodium-MS clustered with the heat tolerant plants F. wislizeni and A. Americana , whereas Chenopodium-NY clustered with the more heat sensitive species. There also were differences between the two ecotypes in the expression of Cp-sHSPs during heat shock. By characterizing the structure, expression and function of Cp-sHSPs from a wide range of species, we hope to determine how differences in these characteristics contribute to heat tolerance.