Tübingen, Germany
Eberhard-Karls-University

Isolation of a new root mutant rum1 affected in lateral and seminal root initiation

--Woll K, Hochholdinger F

The early root system of maize consists of embryonically formed primary and seminal roots. Both root types form lateral roots a few days after emergence (Hochholdinger et al.: Trends Plant Sci., in press, 2004).

Two thousand Mu-tagged F₂-families of maize were visually screened for aberrant root phenotypes on 10-day-old seedlings which led to the identification of a new monogenic recessive mutant. The new root mutant rum1 (rootless with undetectable meristems 1) is affected in lateral root initiation at the primary root and is completely devoid of seminal roots (Fig. 1). Histological analyses of cross sections obtained from embryos 30 days after pollination indicated that mutant in contrast to wild-type embryos do not develop seminal root primordia (Fig. 2). The previously described lateral root initiation mutant lrt1 (Hochholdinger and Feix, Plant J. 16:247-255, 1998) does not initiate lateral roots at the primary and seminal roots and is affected in crown root formation at the coleoptilar node. In contrast to the phenotype of lrt1, the mutant rum1 does not form seminal roots but normal crown roots at the coleoptilar node. Hence, the mutant rum1 defines a new developmental window of root formation comprising late embryogenesis (seminal roots) and early postembryonic root development (lateral roots on the primary root). A detailed molecular and genetic analysis of this new mutant is in progress.

Figure 1. Wild-type (A) and rum1 (B) seedlings 12 days after germination.

Figure 2. Cross section of embryos 30 days after pollination. Arrows in wild-type (A) indicate position of seminal root primordia which are missing in rum1 (B).