A major locus involved in the formation of the radial oxygen loss barrier in adventitious roots of teosinte Zea nicaraguensis is located on the short‐arm of chromosome 3

Abstract

A radial oxygen loss (ROL) barrier in roots of waterlogging-tolerant plants promotes oxygen movement via aerenchyma to the root tip, and impedes soil phytotoxin entry. The molecular mechanism and genetic regulation of ROL barrier formation are largely unknown. Zea nicaraguensis, a waterlogging-tolerant wild relative of maize (Zea mays ssp. mays), forms a tight ROL barrier in its roots when waterlogged. We used Z. nicaraguensis chromosome segment introgression lines (ILs) in maize (inbred line Mi29) to elucidate the chromosomal region involved in regulating root ROL barrier formation. A segment of the short-arm of chromosome 3 of Z. nicaraguensis conferred ROL barrier formation in the genetic background of maize. This chromosome segment also decreased apoplastic solute permeability across the hypodermis/exodermis. However, the IL and maize were similar for suberin staining in the hypodermis/exodermis at 40 mm and further behind the root tip. Z. nicaraguensis contained suberin in the hypodermis/exodermis at 20 mm and lignin at the epidermis. The IL with ROL barrier, however, did not contain lignin in the epidermis. Discovery of the Z. nicaraguensis chromosomal region responsible for root ROL barrier formation has improved knowledge of this trait and is an important step towards improvement of waterlogging tolerance in maize.

Regulation of Root Traits for Internal Aeration and Tolerance to Soil Waterlogging-Flooding Stress

“…The higher root porosity of Z. nicaraguensis than of IL#468 is expected to contribute to the higher ROL levels in the root tips of Z. nicaraguensis. Photographs in B and data in C are reproduced from Watanabe et al (2017) with permission from John Wiley & Sons. Colmer, 2003b).…”

“…An inducible root ROL barrier forms in some waterlogging-tolerant wild relatives of upland crops, such as Hordeum marinum (McDonald et al, 2001;Garthwaite et al, 2003;Kotula et al, 2017) and Z. nicaraguensis (Abiko et al, 2012;Watanabe et al, 2017). The ability to hybridize these waterlogging-tolerant species with their crop relatives presents an opportunity for crop improvement and for studies of the genetic regulation of traits contributing to waterlogging tolerance.…”

“…The recent discovery that a chromosome segment introgression line expresses tight ROL barrier formation in adventitious roots (Fig. 3, B and C; Watanabe et al, 2017) is an exciting development toward a better understanding of this root trait and for the capacity to incorporate it into maize via breeding. The segment was from the short arm of chromosome 3 and was ;22.6 Mb, so fine-mapping work is needed to develop molecular markers for use in markerassisted breeding of this root trait, for which phenotyping is somewhat laborious, as well as to help in the eventual identification of the candidate gene(s).…”

“…The segment was from the short arm of chromosome 3 and was ;22.6 Mb, so fine-mapping work is needed to develop molecular markers for use in markerassisted breeding of this root trait, for which phenotyping is somewhat laborious, as well as to help in the eventual identification of the candidate gene(s). The use of mutant lines and transgenic plants to test specific candidate genes, with phenotyping using the oxygen indicator dye Methylene Blue followed by quantitative measurements using root-sleeving oxygen electrodes (as described by Watanabe et al [2017]; Fig. 3, B and C), should enable the continuation of the recent gains in knowledge of the root ROL barrier trait.…”

Rice acclimation to soil flooding: Low concentrations of organic acids can trigger a barrier to radial oxygen loss in roots

“…However, the signalling network involved is unknown (Colmer et al, ; Yamauchi et al, ). The increased resistance to radial movement of O 2 is associated with deposition of suberin and/or lignin in the hypodermal or exodermal cell walls in roots of rice (Kotula et al, ; Watanabe, Nishiuchi, Kulichikhin, & Nakazono, ) and other species (Kotula, Schreiber, Colmer, & Nakazono, ; Soukup, Armstrong, Schreiber, Franke, & Votrubová, ; Watanabe et al, ; Yamauchi et al, ), although induction of a ROL barrier can occur within 2 days and the changes involved are more subtle than those detectable using histochemical stains (Shiono et al, ). Similar to the lack of any clear histochemical difference for roots of rice with a functional ROL barrier induced by 2 days in stagnant agar medium as compared with aerated controls (Shiono et al, ), in the present study, the staining for suberin of root cross sections at 50 mm behind the root apex, a position with ROL barrier induction (Figure ), also did not show any marked differences for suberin in the hypodermal or exodermal layer (Figure ).…”