Originally published as Genetics Published Articles Ahead of Print on September 14, 2009.

Genetics, Vol. 183, 853-860, November 2009, Copyright © 2009
doi:10.1534/genetics.109.106013

In Planta Mutagenesis Determines the Functional Regions of the Wheat Puroindoline Proteins

L. Feiz*, B. S. Beecher{dagger}, J. M. Martin* and M. J. Giroux*,1

* Department of Plant Sciences and Plant Pathology, Montana State University, Bozeman, Montana 59717-3150 and {dagger} U. S. Department of Agriculture–Agricultural Research Service, Western Wheat Quality Laboratory, Washington State University, Pullman, Washington 99163-6394

1 Corresponding author: Department of Plant Sciences, Montana State University, 119 Plant Bioscience Bldg., Bozeman, MT 59717-3150.
E-mail: mgiroux{at}montana.edu

In planta analysis of protein function in a crop plant could lead to improvements in understanding protein structure/function relationships as well as selective agronomic or end product quality improvements. The requirements for successful in planta analysis are a high mutation rate, an efficient screening method, and a trait with high heritability. Two ideal targets for functional analysis are the Puroindoline a and Puroindoline b (Pina and Pinb, respectively) genes, which together compose the wheat (Triticum aestivum L.) Ha locus that controls grain texture and many wheat end-use properties. Puroindolines (PINs) together impart soft texture, and mutations in either PIN result in hard seed texture. Studies of the PINs' mode of action are limited by low allelic variation. To create new Pin alleles and identify critical function-determining regions, Pin point mutations were created in planta via EMS treatment of a soft wheat. Grain hardness of 46 unique PIN missense alleles was then measured using segregating F2:F3 populations. The impact of individual missense alleles upon PIN function, as measured by grain hardness, ranged from neutral (74%) to intermediate to function abolishing. The percentage of function-abolishing mutations among mutations occurring in both PINA and PINB was higher for PINB, indicating that PINB is more critical to overall Ha function. This is contrary to expectations in that PINB is not as well conserved as PINA. All function-abolishing mutations resulted from structure-disrupting mutations or from missense mutations occurring near the Tryptophan-rich region. This study demonstrates the feasibility of in planta functional analysis of wheat proteins and that the Tryptophan-rich region is the most important region of both PINA and PINB.