Regulation of (1,3;1,4)-beta-glucan synthesis in barley (Hordeum vulgare L.) endosperm and leaf tissues.

Abstract

This project was carried out to explore the regulatory mechanism for (1,3;1,4)-β-glucan synthesis in barley (Hordeum vulgare L.) in both endosperm and leaf tissues. For the grain (1,3;1,4)-β-glucan content regulation study, transcriptional profiles of candidate genes involved in (1,3;1,4)-β-glucan synthesis and degradation, from the developing barley endosperm, were compared across parental lines that had been previously used for grain (1,3;1,4)-β-glucan QTL studies. Correspondence between differences in transcript levels of selected genes and the QTL detected in parental lines was analysed. In the high (1,3;1,4)-β-glucan parent of a mapping population with a grain (1,3;1,4)-β-glucan QTL near/at the location of the HvCslF6 gene, HvCSLF6 transcript levels increased sharply late in endosperm development. In contrast, HvCslF6 transcript levels did not differ between parents of a mapping population in which no grain (1,3;1,4)-β-glucan QTL had been mapped near/at the HvCslF6 gene. Co-transcription of a β-glucan exo-glucanase gene, HvExoIV gene with HvCslF9 early in endosperm development and with HvCslF6 late in endosperm development indicated that HvEXOIV could be involved in (1,3;1,4)-β-glucan synthesis. It has been reported that leaf (1,3;1,4)-β-glucan is degraded when plants are incubated in the dark for prolonged periods and is re-synthesized upon re-exposure to a normal day/night cycle. Thus, to investigate the regulation of leaf (1,3;1,4)-β-glucan, the transcript levels of (1,3;1,4)-β-glucan synthase genes and related genes were profiled during (1,3;1,4)-β-glucan mobilization upon dark incubation. Some of the genes that responded to prolonged dark incubation showed diurnal transcription patterns, even in continuous darkness. Among the (1,3;1,4)-β-glucan synthase candidate genes, only HvCslH1 was up-regulated upon dark incubation. Its transcripts quickly returned to control levels upon re-exposure to the normal day/night cycle. None of the (1,3;1,4)-β-glucan synthase genes were up-regulated upon re- exposure to normal day/night cycles. Consistent with what was observed for HvExoIV, HvCslF6 and HvCslF9 in developing endosperm, HvExoIV seemed to exhibit co-transcription gene with the HvCslH1.