R. Vogelilange et al., DEVELOPMENT, HORMONAL, AND PATHOGENESIS-RELATED REGULATION OF THE TOBACCO CLASS-I BETA-1,3-GLUCANASE-B PROMOTER, Plant molecular biology, 25(2), 1994, pp. 299-311
The class I beta-1,3-glucanases are antifungal vacuolar proteins impli
cated in plant defense that show developmental, hormonal, and pathogen
esis-related regulation. The tobacco enzymes are encoded by a small ge
ne family with members derived from ancestors related to the present-d
ay species Nicotiana sylvestris and N. tomentosiformis, We studied the
expression in transgenic tobacco plants of a chimeric beta-glucuronid
ase (GUS) reporter gene fused to 1.6 kb of upstream sequence of the to
bacco class I beta-1,3-glucanase B (GLB) gene, which is of N. tamentos
iformis origin. Expression of the GUS reporter gene and the accumulati
on of class I beta-1,3-glucanase and its mRNA showed very similar patt
erns of regulation. In young seedlings the reporter gene was expressed
in the roots. In mature tobacco plants it was preferentially expresse
d in lower leaves and roots and was induced in leaves by ethylene trea
tment and by infection with tobacco mosaic virus (TMV). Furthermore, i
t was down-regulated in cultured leaf discs by combinations of the hor
mones auxin and cytokinin. Histological studies of GUS activity showed
that the GLB promoter shows highly localized expression in roots of s
eedlings. It is also expressed in a ring of cells around necrotic lesi
ons induced by TMV infection, but not in cells immediately adjacent to
the lesions or in the lesions themselves. The results of deletion ana
lyses suggest that multiple positive and negative elements in the GLB
promoter regulate its activity. The region from -1452 to -1193 contain
ing two copies of the heptanucleotide AGCCGCC, which is highly conserv
ed in plant-stress and defense-related genes, is necessary for high le
vel expression in leaves. Additional regions important for organ-speci
fic and regulated expression were: -568 to -402 for ethylene induction
of leaves; -402 to -211 for expression in lower leaves and cultured l
eaf discs and for TMV induction of leaves; and -211 to -60 for express
ion in roots.