The expression of mRNAs for light-stress proteins in barley: Inverse relationship of mRNA levels of individual genes within the leaf gradient

Abstract

Two cDNAs coding for putative light-stress proteins of barley (Hordeum vulgare L.) were cloned and the expression of the corresponding mRNAs analyzed in the barley leaf and compared to that of the well-studied ELIP (early-inducible protein) mRNA. During greening the mRNA for clone HL No. 2, which shows homology to two rice proteins of as yet unknown function, was transiently induced; its level rose more slowly and remained elevated for a longer time than was described for ELIP mRNAs. The mRNA corresponding to clone HL No. 13 was recognized as homologous to subunit P of pea glycine decarboxylase, a nuclear-encoded mitochondrial protein involved in photorespiration. Its mRNA level rose more slowly with cellular development than that of the mRNA for LHC II, the apoprotein of the chlorophyll-a/b-binding protein of PSII. The mRNAs of both novel proteins were induced by high light up to an irradiance of 2000 W.m-2. Their levels remained elevated under high light for up to 9 h, the longest time span examined, while after return to culture light conditions the mRNAs rapidly decayed, each with an individual time course. In green barley leaves the mRNA for clone HL No. 2 was expressed to the highest level in the most basal segment, similar to that of ELIPs, while in contrast the mRNA for subunit P of glycine decarboxylase accumulated to the highest level in the leaf apex where the fully developed cells and mitochondria reside. The latter finding strongly indicates that photorespiration is regulated by high light also at the level of mRNA transcription or mRNA accumulation. In addition, we show that perception of light stress is under the control of cellular development and differentiation.

The 23-kDa light-stress-regulated heat-shock protein of Chenopodium rubrum L. is located in the mitochondria

“…Regulation by light stress has also been shown for the mRNA of another mitochondrial protein, the subunit P (Potter et al 1996). Thus, it may be concluded that light stress affects plastids and mitochondria via a closely related, or even an identical, signal transduction pathway.…”

“…Interestingly, the same type of regulation has also been obtained for HSP26 of barley which is undoubtedly localized in the plastids (Stapel et al 1993). This observation strongly indicates that mitochondria are subject to changes in light-stress-regulated gene expression, especially under conditions of heat stress, as are a number of proteins in the chloroplast (Adamska et al 1992;Potter et al 1996).…”

Posttranscriptional control in the expression of the genes coding for high-light-regulated HL#2 proteins

“…The deduced amino acid sequence of HL#2 (PoÈ tter et al 1996) shows similarities to the deduced amino acid sequences of two proteins from rice (Claes et al 1990;de Pater et al 1992) again of unknown function, but apparently also involved in the stress response. A recent repeat of the search in the Swiss protein bank revealed quite a number of other proteins with homology to HL#2 protein; the most remarkable similarities were to lectins (Skea et al 1988;Geshi and Brandt 1998) and to two jasmonate-inducible proteins (Lee et al 1996).…”

“…Long-lasting light stress will be harmful to plants and will activate stress genes within hours or days. Previously, we have shown that the mRNA for a light-inducible protein, designated HL#2, is induced by high light¯uxes that are experienced as light stress by barley cells (PoÈ tter et al 1996). The expression of the mRNA was regulated in a way very similar to those coding for early light-inducible proteins (ELIPs; Adamska et al 1992;PoÈ tter and Kloppstech 1993).…”

“…Interestingly, another light-stress-enhanced mRNA which codes for subunit P of glycine decarboxylase (Turner et al 1992) was upregulated by high light but in a rather distinct manner. In contrast to the ELIP and HL#2 mRNAs, its level was highest in the apical part of the leaf, indicating an expression which might be positively correlated with the development or function of plastids and the photosynthetic capacity of thylakoid membranes (PoÈ tter et al 1996).…”