A NAC transcription factor NTL4 promotes reactive oxygen species production during drought‐induced leaf senescence in Arabidopsis

Abstract

SUMMARYReactive oxygen species (ROS) are produced in plant cells primarily as by-products of aerobic energy metabolism. They are also generated during plant adaptation responses to environmental stresses, such as drought and high salinity. Therefore, plants have evolved ROS-detoxifying enzymes and antioxidants to cope with ROS accumulation. However, if stress conditions are prolonged, the level of ROS will surpass the capacity of the detoxifying machinery, causing oxidative damage to cellular constituents. It is known that ROS act in abscisic acid-mediated stress responses to sustain plant survival under adverse growth conditions. However, it is largely unknown how ROS metabolism is linked to stress responses. Here, we show that a droughtresponsive NAC transcription factor NTL4 promotes ROS production by binding directly to the promoters of genes encoding ROS biosynthetic enzymes during drought-induced leaf senescence. Leaf senescence was accelerated in 35S:4DC transgenic plants over-expressing an active form of NTL4 under drought conditions. The 35S:4DC transgenic plants were hypersensitive to drought, and ROS accumulated in the leaves. In contrast, ROS levels were reduced in NTL4-deficient ntl4 mutants, which exhibited delayed leaf senescence and enhanced drought resistance. These observations indicate that NTL4 acts as a molecular switch that couples ROS metabolism to drought-induced leaf senescence in Arabidopsis.

Regulation of reactive oxygen species generation under drought conditions in Arabidopsis

“…Under drought conditions, whereas the ROS levels were drastically elevated in the 35S:4ΔC transgenic leaves, they were reduced in the ntl4 mutant leaves. 5 These observations support that the NTL4 gene is related with accumulation of ROS under drought conditions. It has been known that drought stress disrupts the balance between ROS and antioxidant levels, causing ROS accumulation and inducing leaf senescence.…”

“…5 These observations suggest that the 4ΔC form is closely related with a biologically functional NTL4 form. Notably, the NTL4 gene is significantly induced by drought and heat stresses.…”

“…4 A truncated NTL4 form (4ΔC) lacking the TM motif possesses transcriptional activation activity, and 35S:4ΔC transgenic plants exhibit distinct phenotypes, such as reduced growth and alteration of leaf morphology. 5 These observations suggest that the 4ΔC form is closely related with a biologically functional NTL4 form. Notably, the NTL4 gene is significantly induced by drought and heat stresses.…”

“…5 In addition, endogenous contents of ROS were altered in the 35S:4ΔC transgenic plants and ntl4-1 mutants. Under drought conditions, whereas the ROS levels were drastically elevated in the 35S:4ΔC transgenic leaves, they were reduced in the ntl4 mutant leaves.…”

“…Notably, the NTL4 gene is significantly induced by drought and heat stresses. 5 Diverse plant developmental processes, such as germination and leaf senescence, are profoundly affected by environmental stresses. 6,7 We therefore examined the potential role of the NTL4 gene in drought stress responses.…”