In fungi, L-rhamnose (Rha) is converted via four enzymatic steps into pyruvate and L-lactaldehyde, which enter central carbon metabolism. In Aspergillus niger, only the genes involved in the first three steps of the Rha catabolic pathway have been identified and characterized, and the inducer of the pathway regulator RhaR remained unknown. In this study, we identified the gene (lkaA) involved in the conversion of L-2-keto-3-deoxyrhamnonate (L-KDR) into pyruvate and L-lactaldehyde, which is the last step of the Rha pathway. Deletion of lkaA resulted in impaired growth on L-rhamnose, and potentially in accumulation of L-KDR. Contrary to ΔlraA, ΔlrlA and ΔlrdA, the expression of the Rha-responsive genes that are under control of RhaR, were at the same levels in ΔlkaA and the reference strain, indicating the role of L-KDR as the inducer of the Rha pathway regulator.

在真菌中，L-鼠李糖 (Rha)通过四个酶促步骤转化为丙酮酸和 L-乳醛，进入中心碳代谢。在黑曲霉中，仅鉴定和表征了参与 Rha 分解代谢途径前三个步骤的基因，并且途径调节剂 RhaR 的诱导物仍然未知。在这项研究中，我们鉴定了参与 L-2-酮-3-脱氧鼠李酸 (L-KDR) 转化为丙酮酸和 L-乳醛的基因 ( lkaA )，这是 Rha 途径的最后一步。 LkaA的缺失导致 L-鼠李糖生长受损，并可能导致 L-KDR 的积累。与 Δ lraA、 Δ lrlA和 Δ lrdA相反，在 RhaR 控制下的 Rha 反应基因的表达在 Δ lkaA和参考菌株中处于相同水平，表明 L-KDR 作为诱导剂的作用Rha 通路调节因子。