Meeting the Challenge of Yellow Rust in Cereal Crops - ICARDA

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Molecular characterization of wheat BI-1 homologues that
weaken the hypersensitive reaction triggered by stripe
[yellow] rust fungus
X. Wang, J. Lv, P. Ji, L. Deng, X. Liu, L. Huang and Z. Kang
College of Plant Protection and Shaanxi Key Laboratory of Molecular Biology for
Agriculture, Northwest A & F University, Yangling, Shaanxi, China
Programmed cell death (PCD) is a genetically controlled process that plays a
vital role in the development, differentiation and disease resistance of higher
organisms. To date, a few homologues of animal PCD regulators have been
identified in plants. Among these is the plant Bax Inhibitor-1 (BI-1) protein,
which is a conserved cell death regulator protein that inhibits mammalian BAX
induced cell death in yeast. The role of BI-1 in the regulation of plant PCD
remains to be elucidated. Plant BI-1 genes have been isolated from various
plant species such as rice, Arabidopsis, tobacco, Brassica napus and barley. We
cloned a TaBI-1 from cDNA libraries of cv. Suwon 11 wheat challenged by
Puccinia striiformis f.sp. tritici (Pst). Sequence analysis of TaBI-1 revealed an
open reading frame of 1095 nucleotides, which encodes a predicted protein of
247 amino acids and shares 97% identity with barley BI-1. A variety of
computer algorithms predict unambiguously that TaBI-1 contains seven transmembrane
domains with an N terminal signal peptide. Hydropathy analysis
and targeting-motif detection for TaBI-1 predicted proteins strongly suggest
their association with plant membranes. According to PSORT, iPSORT and
ChloroP programmes, TaBI-1 proteins can be located within the thylakoid
membranes. At the same time, basic residues at their C-terminal end look like
some nuclear targeting sequences, which are also detected by PSORT.
Phylogenetic analysis and protein alignment reveal that similarity between the
predicted proteins spans the entire length of the sequence, except for the N-
termini, where many amino acids are lacking in the alignment. Divergence
between predicted sequences is represented as an inferred tree. It is
noteworthy that plant sequences are grouped together and apart from animal
sequences, with a separation between monocotyledonous and dicotyledonous
species. This inferred tree is thus closely related to accepted evolutionary
classification. TaBI-1 gene expression was studied in the leaves of wheat cv.
Suwon 11 inoculated with urediospores of a compatible race CYR31 and
incompatible race CYR23 of Pst and treated with SA, JA and ETH. Wheat
leaves show low basal expression of TaBI-1 (indicated by 0 h). After the
inoculation of CYR23, TaBI-1 expression was transiently repressed (12 hpi),
followed by slight induction (24 hpi), and recovery at 48–72 hpi equally for
mock-treated plants (0 h), finally peaked at 120 hpi. qRT-PCR analysis showed