sparse inflorescence1, barren inflorescence1 and barren stalk1 promote cell elongation in maize inflorescence development

Abstract

The sparse inflorescence1 (spi1), Barren inflorescence1 (Bif1), barren inflorescence2 (bif2), and barren stalk1 (ba1) mutants produce fewer branches and spikelets in the inflorescence due to defects in auxin biosynthesis, transport, or response. We report that spi1, bif1, and ba1, but not bif2, also function in promoting cell elongation in the inflorescence.

Figure 1.—

Genetic interaction of spi1 with bif2. Double mutants were constructed in the B73 background with bif2-77 and spi1-ref alleles, which were genotyped as previously described (Gallavotti et al. 2008). For analysis of immature spi1; bif2 double mutants, tassels were dissected from 5-week-old plants, and fixation and SEM was carried out as previously described (Barazesh and McSteen 2008a). For mature plant analysis, all plants were grown in the field to maturity. Two families of 120 kernels were planted at two different field locations. (A) Mature tassel phenotype of all genetic classes in a family segregating for both spi1 and bif2. (B–E) SEM analysis of developing inflorescences of (B) normal, (C) spi1, (D) bif2, and (E) spi1;bif2 double mutants. Arrowhead indicates spikelets growing over the tip of the spi1 mutant tassel. IM, inflorescence meristem; SPM, spikelet pair meristem. Bar, 100 μm. (F) Mature tassel length of all genetic classes in a family segregating for both spi1 and bif2. Tassel length was measured from the node at the base of the flag leaf to the tip of the tassel. Sample size was 10 for each genetic class.

Figure 2.—

spi1, Bif1, and ba1 have reduced cell elongation. Nail polish impressions of epidermal cells from the base of the mature tassel in (A) normal, (B) spi1, (C) Bif1, and (D) ba1. Bar, 100 μm.

Figure 3.—

Genetic interaction of spi1 with Bif1 and of spi1 with ba1. (A) Mature tassel phenotype of a spi1, Bif1 segregating family. Double mutants were constructed in the B73 genetic background with the spi1-ref and Bif1-N1440 alleles (Barazesh and McSteen 2008a; Gallavotti et al. 2008). Plants were genotyped for the spi1-ref allele as reported (Gallavotti et al. 2008). A total of 120 plants were analyzed in two different field locations. (B) Mature tassel phenotype of a spi1, ba1 segregating family. Double mutants were constructed in the B73 genetic background with the spi1-ref and ba1-ref alleles and genotyped as described (Barazesh and McSteen 2008a; Gallavotti et al. 2008). A total of 120 plants were analyzed in two different field locations. (C) Close-up of the surface of the tassel rachis showing prominent bract leaf primordia in ba1 (arrowhead), which are not present in spi1; ba1.