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

Authors: MATTHES, MICHELA - University Of Bonn; Best, Norman; ROBIL, JANLO - Ateneo De Manila University; MCSTEEN, PAULA - University Of Missouri

Submitted to: Journal of Plant Nutrition and Soil Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/8/2023
Publication Date: 9/22/2023
Citation: Matthes, M.S., Best, N.B., Robil, J.M., McSteen, P. 2023. Enhancement of developmental defects in the boron-deficient maize mutant tassel-less1 by reduced auxin levels. Journal of Plant Nutrition and Soil Science. https://doi.org/10.1002/jpln.202300155.
DOI: https://doi.org/10.1002/jpln.202300155

Interpretive Summary: The essential micronutrient, boron, is necessary for the structural function of plant cell walls. Deficiencies in boron cause many deleterious consequences that cannot be explained solely by alterations in the cell wall. Many boron deficient mutants resemble hormone deficient mutants, specifically mutants in auxin biosynthesis and signaling. Previous research on boron deficiency mutants has concentrated on root development, primarily in the model species Arabidopsis, and has not closely investigated boron’s role in plant stem cells (meristems). To investigate boron's role in other plant developmental processes in maize, we conducted double mutant analysis between boron and auxin mutants involving hormone quantification and hormone transporter localization experiments to investigate effects on meristem development. We identified developmentally specific interactions between boron and auxin, specifically in shoot and floral meristems, where a loss of auxin worsened the boron deficient traits. These findings open a new research field on boron control of plant architecture by identifying its interaction with the plant hormone auxin.

Technical Abstract: 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.