Maize Genetics Cooperation Newsletter vol 85 2011

MILANO, ITALY

Universit� degli Studi di Milano - Dipartimento di Produzione Vegetale

Isolation and preliminary characterization of a new maize low phytic acid 1 allele

--Cerino Badone, F; Lago, C; Bucci, A; Cassani, E; Pilu, R

Phytic acid, myo-inositol 1,2,3,4,5,6-hexakisphosphate (IP6), is the major storage form of phosphorous in plants, it�s mainly accumulated in pollen and seeds (up to 4-5% of dry weight). In maize kernel the 80% of phytic acid is localized in the scutellum while the remaining 20% in the aleuronic layer. During germination phytic acid is idrolized by phytases. Both phytic acid and the cations that it�s able to bond are poorly bio-available for monogastric animals due to their lack of phytase activity. One strategy to solve this problem is the isolation of cereal mutants able to accumulate low level of phytic P and high level of free phosphate in the seeds.

We obtained a mutant population by the EMS (ethyl methanesulfonate) seed-treatment and approximately 300 M2 families were screened using the molybdate staining method for free phosphate.

We found one low phytic acid 1 mutant (named lpa1-7); the 3:1 segregation ratio of lpa1-7, observed in the F2 generation, indicated a monogenic recessive defect (Tab. 1).

The lpa1-7 mutation causes approximately a ten fold increase in the amount of free phosphate (Fig. 1) and a reduction of about 80 % of phytic acid (Fig. 2); the presence of this new allele in homozygous condition is lethal. Germination could be partially restored by embryo-rescue, embryos from mature seeds cultured in MS medium grew slower than the wild type and some defective seedlings were observed. Mutant embryos displayed a reduction in dimension and alteration in the alignment of the shoot and root primordia.

The relationship of our low phytic acid mutation with the previously identified low phytic acid maize mutations was tested. It�s known that the lpa1 mutant is the only low phytic acid mutant exhibiting more than 60% of reduction of phytic acid, the rate of reduction shown by lpa1-7 acid suggested that it could be an lpa1 allele. The mutants lpa1, lpa2 and lpa1-7 were crossed inter se in all pairwise combinations to assay their pattern of complementation. The results obtained showed that the lpa1 mutant failed to complement lpa1-7, suggesting its allelic nature (Tab. 2).

Genetic analysis of this mutation, as well as its biochemical characterization are under way.

	Genetic test	segregation		χ^2	p
		wt	mutant
+/lpa1-7	F2	159	51	0.057	0.8113

Table 1: Segregation of +/lpa1-7 phenotypes observed in the F2 progenies obtained by selfing.

	lpa1	lpa2	lpa1-7
lpa1	-	+	-
lpa2		-	+
lpa1-7			-

Table 2: Complementation test among lpa1, lpa2 and lpa1-7

Figure 1: Mature dry seeds of the indicated genotypes were assayed for seed phytic acid P expressed as P concentrations (atomic wt = 31)

Figure 2: Mature dry seeds of the indicated genotypes were assayed for free inorganic P expressed as P concentrations (atomic wt = 31)

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