We have identified a gene, SHORT LATERAL ROOT LENGTH1 (SLL1), which is important for the elongation of lateral roots in rice. An sll1 mutant has decreased lateral root growth due to a defect in the cell elongation. The SLL1 gene encodes a member of the stearoyl-acyl carrier protein fatty acid desaturase family that is the key regulator of overall fatty acid desaturation in plants. We measured the fatty acid content and found that the 18:0 content in the sll1 mutant root was approximately 4 times that in the wild-type root. When the sll1 mutant was grown at 33 °C, it complemented the mutant phenotype to a moderate level, which reflects the importance of the low 18:0 content in maintaining the cell membrane structure. The SLL1 gene was expressed at the lateral root tip, whereas SLL1 expression was not detected in the elongation zone of the crown roots. These results indicate that the lateral root specific defect in sll1 mutant is caused by the different expression patterns of SLL1 in lateral and crown roots. In addition, SLL1 over-expressers produced significantly longer lateral roots compared to the wild-type, and thus SLL1 gene would be very useful for improving rice root architecture.
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