Mortal: A Mutant of White Clover Defective in Nodal Root Development

Abstract

A monogenic dominant mutant of white clover (Trifolium repens L.), designated Mortal, which is defective in the formation of adventitious nodal roots, is described. Mortal plants grown at temperatures ranging from 10 to 25°C do not initiate nodal root primordium development. However, all other aspects of plant development are normal, including the formation of lateral roots and wound-induced adventitious roots. In some genetic backgrounds, the Mortal mutation has a temperature-sensitive conditional phenotype. Mortal plants shifted from growing conditions of 20 to 30°C for 2 to 3 d form nodal root meristems. However, new nodes that develop after plants are returned to 20°C exhibit the mutant phenotype. The capacity to form nodal roots on cuttings placed in water is also influenced by the genetic background of the Mortal mutation. Genetic analysis established that the physiological reversion of Mortal to nodal root formation is controlled by at least two separate dominant genetic loci, one for Nodal water response (Now) and one for Nodal temperature response (Not); the Now locus has a dominant epistatic interaction with the Not locus. The conditional nature of Mortal should provide opportunities for the identification of genetic and physiological mechanisms that influence the development of nodal roots.Whereas the basic structure of angiosperms is established during embryogenesis, most organs are formed by postembryonic development (Esau, 1977). Generally, all of the shoot structures (leaves, nodes, internodes, axillary shoot meristems, and flowers) are derived from the primary shoot apical meristem. However, adventitious shootborne roots are an exception because they develop endogenously from differentiated parenchyma cells close to the vascular tissues (Lovell and White, 1986).Little is known about the genes that control adventitious shoot-borne root morphogenesis, despite their importance for anchorage, nutrient acquisition, and water uptake from the soil in a wide range of plant species. One approach to understanding the genetic mechanisms that underlie adventitious root initiation and development is to identify and characterize mutants altered in the process. At present, few mutants with defects in adventitious root development are known (Schiefelbein and Benfey, 1991). There are mutants of tomato that produce few or no adventitious roots (Butler, 1954;Zobel, 1991) and mutants of maize that are defective in the formation of lateral seminal roots, crown roots, or both lateral seminal and crown roots (Jenkins, 1930; de Miranda, 1980;Hetz et al., 1996).The general unpredictability in the formation of secondary roots on shoots complicates the analysis of the genetic and molecular mechanisms controlling adventitious root development. This can be minimized by characterizing the genetic control of the formation of adventitious nodal root primordia. In some plant species, adventitious root primordia arise in a precise and ordered manner during node development. One such example is the nodal roots that form on the pro...

A generic individual-based model to simulate morphogenesis, C–N acquisition and population dynamics in contrasting forage legumes

“…The greater number of root apices produced by multiple sub-root systems each receive a lower proportion of the amount of C allocated to roots, resulting in reduced root elongation rates. This behaviour produced plant phenotypes globally consistent with root mutants reported for white clover: larger and deeper seminal taproot in nodal mutants as compared to wild types (White et al, 1998;Thomas, 2003), and preferential development of nodal roots from phytomers connected with vigorous axillary branches in wild types (Thomas et al, 2002).…”

Progress in breeding perennial clovers for temperate agriculture

“…The development of a strong network of stolons is a prerequisite of persistence and stolon characters have been a major focus of breeding efforts (Caradus & Chapman 1996;Collins et al 1997;Sanderson et al 2003). White et al (1998), in their studies of a white clover defective in nodal root development, present a novel approach to ascertaining the importance of this trait.…”

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“…When the development of nodal root systems is prevented, either by growing plants under dry conditions or in the mutant Mortal in which nodal rooting is suppressed (White et al 1998) (Figure 6C), carbon allocation to the roots is directed totally to the crown tap root, which grows larger than in wildtype plants as a result. Thus, the development of both tap roots and nodal root systems on the same plant inevitably leads to compromise.…”