COMMON BEAN (Phaseolus vulgaris) BIOFORTIFICATION: UNEXPECTED EFFECTS OF THE lpa1-1 MUTATION ON LECTIN STABILITY AND IDENTIFICATION OF A NEW lpa MUTANT

Phytic acid (InsP6) is the main storage form for phosphate in seeds and in the plant it plays an important role in signal transduction in response to environmental stress and hormonal changes. InsP6 is a strong chelator of mono and divalent cations, such as iron, zinc, magnesium and calcium, essential minerals in the diet, reducing their bioavailabilty. We previously isolated the common bean lpa1-1 mutant, affected in the PvMRP1 gene, coding for a putative tonoplastic phytic acid transporter (1). Phytic acid is a major inhibitor of iron bioavailability from beans and might limit the positive effect of biofortified beans on iron status of consumers. The lpa beans were tested in two different studies to verify if they provide more bioavailable iron than biofortified beans in a bean consuming population (2,3). Results from both studies showed that biofortified and lpa beans provide more bioavailable iron than normal beans and could thus contribute to a reduction in iron deficiency. However, in the frame of the second study, carried out on Rwandese women displaying a low iron status by stable iron isotope technique using a multiple meal crossover design, it was found that the lpa beans caused transient adverse digestive side effects in the participants. Gel electrophoresis analysis showed lectin residuals in the cooked lpa beans. Subsequent cooking trials with different lpa bean varieties indicated that lectin stability depended on the genetic background of the beans. The interaction of bean lectins with lpa1-1 mutation is currently under investigation. Moreover, with the aim to isolate new common bean lpa mutants we screened an EMS population and identified a new lpa mutant, named lpa1-2 as it resulted allelic to lpa1-1 mutant. The lpa1-2 mutation consists in a premature stop codon in the first exon of the PvMRP1 gene. Data regarding the phenotypic characterization of the lpa1-2 mutant will be presented.