The genetic control of lateral root formation has been studied in great detail in the dicotyledonous plant Arabidopsis, but in contrast very little is known about its genetic basis in monocotyledonous plants like maize. The only mutants isolated so far in maize are lrt1, which is transiently defective in lateral root initiation during early postembryogenic root growth (Plant J. 16:247-255, 1998), and slr1, which forms only short lateral roots at the young seedling stage (MNL 72:30, 1998). We now report the isolation of slr2, which is very similar in its phenotype to slr1 and leads to the formation of short lateral roots as a result of an impaired cell elongation mechanism. This is demonstrated in the Figure which shows in part A a close-up view of a wt primary root (upper part) in comparison with a slr2 primary root with shorter lateral roots, and in part B, a confocal laser scanning microscopic picture of relevant tissue depicting the cell size differences. The formation of short lateral roots is specific for the early growth periods of the primary- and lateral seminal roots. Later phases of these roots, as well as lateral root formation on crown roots, are not affected. Slr2 does not show the pale yellow appearance of the first two leaves typical for slr1. The mutant slr2 is not allelic to slr1 and slr1/slr2 double mutants display a non-additive phenotype, indicating an interaction of the two loci. We are now in the process of performing allelism tests of slr1 and slr2 with further tentative mutants recently isolated in our lab which are defective in lateral root growth and morphology.
 

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