In the extreme deserts of southern Angola and northern Namibia, one plant species stands out: Welwitschia mirabilis. This ancient gymnosperm is legendary for producing just two aboveground leaves that persist throughout its entire lifespan—leaves that can elongate continuously for thousands of years. Its remarkable durability has earned it the evocative Afrikaans name "tweeblaarkanniedood," or "two leaves that cannot die."

While Welwitschia's resilience to extreme environmental stresses is well-documented, the internal mechanisms governing its leaf aging have long remained a mystery.

Now, researchers from the Wuhan Botanical Garden (WBG) of the Chinese Academy of Sciences have solved part of that puzzle, identifying a specific transcriptional module "WmABF1-1-WmMYB111" that controls the plant's leaf senescence and underpins its survival. Their findings were recently published in Plant Biotechnology Journal.

The team pinpointed that a transcription factor called WmMYB111, acting as an inducible abscisic acid (ABA) receptor, plays a central role. WmMYB111 activates the expression of key genes associated with four critical processes: ABA biosynthesis (via genes known as WmNCEDs), leaf senescence (WmSAGs), chlorophyll degradation (WmCCGs), and nitrogen transport (WmNRTs).

In the ABA signaling pathway, the researchers further found that WmABF1-1—an ABA-responsive element binding factor—acts upstream of WmMYB111. This positioning allows WmABF1-1 to regulate the expression of both WmMYB111 and its downstream target genes, forming a proactive transcriptional cascade regulatory network.

These findings reveal a pivotal module that orchestrates the multidimensional regulatory program of Welwitschia's leaf senescence. Crucially, they also establish a functional link between ABA accumulation in the plant and its efficiency in utilizing nitrogen.

"Understanding how Welwitschia manages its resources and responds to stress could provide insights into how external signals are integrated into a plant's internal age-related information," said Prof. WAN Tao, the corresponding author of the study. "This is the first time we've been able to detail the transcriptional regulation that governs aging in this plant."

This work was supported by the National Natural Science Foundation of China, and the Scientific Research Program of the Sino-Africa Joint Research Center, among others.

The model of the regulation of ABA-induced leaf senescence and nitrogen transport in Welwitschia governed by WmABF1-1-WmMYB111 module. (Image by WBG)