Inheritance of tissue-specific expression of barley hordein promoter-uidA fusions in transgenic barley plants
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Barley (Hordeum vulgare L.) hordeins are alcohol-soluble redundant storage proteins that accumulate in protein bodies of the starchy endosperm during seed development. Strong endosperm-specific β-glucuronidase gene-(uidA; gus) expression driven by B1- and D-hordein promoters was observed in stably transformed barley plants co-transformed with the selectable herbicide resistance gene, bar. PCR analysis using DNA from calli of 22 different lines transformed with B1- or D-hordein promoter-uidA fusions showed the expected 1.8-kb uidA fragment after PCR amplification. DNA-blot analysis of genomic DNA from T0 leaf tissue of 13 lines showed that 12 (11 independent) lines produced uidA fragments and that one line was uidA-negative. T1 progeny from 6 out of 12 independent regenerable transgenic lines tested for uidA expression showed a 3 : 1 segregation pattern. Of the remaining six transgenic lines, one showed a segregation ratio of 15 : 1 for GUS, one expressed bar alone, one lacked transmission of either gene to T1 progeny, and three were sterile. Stable GUS expression driven by the hordein promoters was observed in T5 progeny in one line, T4 progeny in one line, T3 progeny in three lines and T2 or T1 progeny in the remaining two fertile lines tested; homozygous transgenic plants were obtained from three lines. In the homozygous lines the expression of the GUS protein, driven by either the B1- or D-hordein promoters, was highly expressed in endosperm at early to mid-maturation stages. Expression of bar driven by the maize ubiquitin promoter was also stably transmitted to T1 progeny in seven out of eight lines tested. However, in most lines PAT expression driven by the maize ubiquitin promoter was gradually lost in T2 or later generations; one homozygous line was obtained. In contrast, six out of seven lines stably expressed GUS driven by the hordein promoters in T2 or later generations. We conclude that the B1- and D-hordein promoters can be used to engineer, and subsequently study, stable endosperm-specific gene expression in barley and potentially to modify barley seeds through genetic engineering.
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