|Wheat grain hardness results from highly conserved mutations in the friabilin components Puroindoline a and b. Proceedings of the National Academy of Sciences 95:6262-6266
|Giroux,M.J. and Morris,C.F.
USDA/ARS Western Wheat Quality Lab
|"Soft" and "hard"
are the two main market classes of wheat (Triticum aestivum L.) and are distinguished
by expression of the Hardness gene. Friabilin, a marker protein for grain softness
(Ha), consists of two proteins, puroindoline a and b (pinA and pinB, respectively).
We previously demonstrated that a glycine to serine mutation in pinB is linked
inseparably to grain hardness. Here, we report that the pinB serine mutation
is present in 9 of 13 additional randomly selected hard wheats and in none of
10 soft wheats. The four exceptional hard wheats not containing the serine mutation
in pinB express on pinA, the remaining component of the marker protein friabilin.
The absence of pinA protein was linked inseparably to grain hardness among 44
near-isogenic lines created between the soft variety Heron and the hard variety
Falcon. Both pinA and pinB apparently are required for the expression of grain
softness. The absence of pinA protein and transcript and a glycine-to-serine
mutation in pinB are two highly conserved mutations associated with grain hardness,
and these friabilin genes are the suggested tightly linked components of the
Hardness gene. A previously described grain hardness related gene termed "GSP-1"
(grain softness protein) is not controlled by chromosome 5D and is apparently
not involved in gain hardness. The association of grain hardness with mutations
in both pinA and pinB indicates that these two proteins alone may function together
to effect grain softness. Elucidation of the molecular basis for grain hardness
opens the way to understanding and eventually manipulating this wheat endosperm
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