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Characterization of an unusually regulated gene encoding asparagine synthetase in the parasitic plant Striga hermonthica (Scrophulariaceae)
Author(s) -
Simier Philippe,
Delavault Philippe,
Demarsy Emilie,
Pouvreau JeanBernard,
Pageau Karine,
Le Bizec Bruno,
Fer André,
Thalouarn Patrick
Publication year - 2005
Publication title -
physiologia plantarum
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.351
H-Index - 146
eISSN - 1399-3054
pISSN - 0031-9317
DOI - 10.1111/j.1399-3054.2004.00438.x
Subject(s) - biology , striga hermonthica , asparagine synthetase , asparagine , mutant , striga , gene , microbiology and biotechnology , genetics , botany , biochemistry , enzyme , germination
In the parasitic plant Striga hermonthica (Del. Benth), asparagine synthesis plays a prominent role in the metabolism of the host‐derived nitrogen and in the detoxification process of a steady‐state N‐excess. Here, we show that asparagine synthetase (EC 6.3.5.4), the primary enzyme involved in asparagine production in plants, is encoded in Striga by a small gene family, with at least two AS genes, including the gene called ShAS related to the small class II Asparagine Synthetase genes. The functionality of ShAS was demonstrated by complementation of an E. coli asn auxotroph mutant and its expression was characterized by semiquantitative RT‐PCR. The ShAS expression pattern in plants growing under standard light conditions and in light‐grown calli differs from the expression pattern of most plant AS genes since ShAS transcripts accumulated in all the plant organs and this accumulation was not repressed by light. In contrast, ShAS expression was light‐induced in mature leaves and in the chlorophyllous calli. The promoter region of ShAS was also sequenced and characterized and displayed various light‐responsive, as well as potential sugar‐responsive, cis ‐elements. A correlation between ShAS expression and asparagine synthesis was demonstrated in the illuminated mature leaves by 15 N‐labelling in vivo experiments. ShAS was also shown to be positively regulated in light‐grown calli by C‐ and N‐starvation and was associated with senescence‐related protein breakdown. ShAS expression was not repressed by light in haustoria, roots, senescing leaves and inflorescences. These findings show that one or more unknown factors of regulation can override light as the major regulator.