Isolation of a novel lateral-rootless mutant in rice (Oryza sativa L.) with reduced sensitivity to auxin

Lateral roots play an important role in the acquisition of nutrients and anchorage of the whole plant. To better understand the mechanisms underlying lateral root development, we isolated a new lateral-rootless mutant lrt2 in screening for 2,4-dichlorophenoxyacetic acid (2,4-D) resistance in M2 lines of rice (Oryza sativa L. cv. Nipponbare) generated by tissue culture. lrt2 failed to form lateral roots and exhibited altered root response to gravity. Analysis for auxin resistance showed that lrt2 was less sensitive to various auxins including 2,4-D, indole-3-acetic acid (IAA), indole-3-butyric acid (IBA) and 1-naphthaleneacetic acid (NAA) compared with wild type, but was similarly sensitive to auxin transport inhibitor N-1-naphthylphthalamic acid (NPA). This suggests that the reduced sensitivity to auxin in lrt2 might be caused by a disruption in auxin response rather than in auxin transport. Genetic analysis indicated that the lateral-rootless phenotype of lrt2 is due to a recessive mutation. To map the lrt2 gene, we tested molecular markers by bulk segregant analysis. The lrt2 gene was localized to a 10.8 cM interval on the short arm of chromosome 2, flanked by two sequence-tagged site (STS) markers Lrt2P1 and Lrt2P2.