Enhancement of developmental defects in the boron-deficient maize mutant tassel-less1 by reduced auxin levels

Background: Plant responses to deficiencies of the micronutrient boron are diverse and go beyond the well-characterized function of boron in cell wall crosslinking. To explain these phenotypic discrepancies, hypotheses about interactions of boron with various phytohormones have been proposed, particularly auxin. While these hypotheses are intensely tested in the root meristem of the model species, Arabidopsis thaliana, studies in crop species and the shoot are limited.Aims: To address potential boron-auxin interactions during the vegetative and reproductive development of the crop maize (Zea mays), we utilized the boron-deficient tassel-less1 (tls1) mutant and the auxin-deficient vanishing tassel2 (vt2) mutant. We investigated interactions of boron and auxin on the levels of auxin biosynthesis and auxin transport in leaves and shoot meristems.Methods and Results: By using genetic interaction analysis, hormone quantification, and confocal microscopy, we show that boron-deficient leaf phenotypes in tls1 are enhanced in double mutants with vt2 in both greenhouse and field conditions. However, auxin levels are not altered in developing leaves in tls1. Rather, the localization of ZmPIN1a:YFP, a marker for auxin transport, is altered in young tassel meristems and is absent from organ initiation sites during vegetative development.Conclusions: Our data suggest a link between polar auxin transport and phenotypic consequences in boron-deficient conditions and further show that boron deficiency-induced developmental defects are sensitive to low auxin levels. Our study, therefore, offers new insight into nutrient-hormone interactions to regulate crop development.