Homolog Gene Regulation Alters Cell-Cycle Progression for Sprouting Trichomes

Trichomes-tiny hair‑like structures on leaves-serve as physical barriers that protect plants from insect herbivores, UV radiation, excessive water loss, and toxic chemicals. They also contribute to stress tolerance and, in some crops, influence nutritional quality. In Arabidopsis, trichome development is governed by a well‑characterized regulatory network involving transcription factors and cell‑cycle regulators.

However, in wucai, a Brassica vegetable prized for its rich glucosinolates and amino acids, most commercial cultivars are low‑density or completely glabrous. The genetic basis for this trait loss has remained unknown. Based on these challenges, there is a need to conduct in‑depth research on the genetic and molecular mechanisms underlying trichome loss in wucai.

A study published (DOI: 10.1093/hr/uhag184) on May 8, 2026, in Horticulture Research-a journal of Nanjing Agricultural University-reports the identification of a transposon insertion that disrupts trichome formation in wucai (Brassica campestris L.). The research was conducted by scientists from Anhui Agricultural University's School of Horticulture in Hefei, China. Using a combination of bulked segregant analysis sequencing (BSA‑seq) and map‑based cloning, the team pinpointed BcCPR5 -the wucai homolog of Arabidopsis CPR5 (Constitutive Pathogen Response5)-as the key gene controlling trichome density.

The researchers compared two wucai inbred lines: W7‑1, which is densely hairy, and W7‑2, which is largely hairless except for a few trichomes along leaf margins. Genetic analysis showed that the trait is controlled by a single dominant nuclear gene, with a 3:1 segregation ratio in the F2 population. Through progressive fine‑mapping, they narrowed the candidate region to a 114‑kb interval on chromosome A06 and identified BcCPR5 as the causal gene.

The key difference between the two lines turned out to be a 3,365‑base‑pair transposon insertion in the BcCPR5 promoter of W7‑2. This insertion reduced promoter activity by more than 80%, slashing BcCPR5 expression. Virus‑induced gene silencing (VIGS) of BcCPR5 in the hairy line dropped trichome density to one‑sixth of normal levels, confirming the gene's essential role. The team further discovered that the transcription factor BcWRKY44 directly activates BcCPR5 by binding to a W‑box element in its promoter. In W7‑2, the transposon insertion physically separates this W‑box from the transcription start site, blocking activation. Notably, coding‑sequence differences between the two lines-including a 43‑bp deletion and multiple amino‑acid changes-did not affect BcCPR5 function, ruling out protein‑level defects as the cause.

"The transposon insertion basically cuts the communication line between the activator and the gene," the authors said. "BcWRKY44 can still bind to the promoter, but the insertion puts a physical barrier between the binding site and the transcription start site, so activation never reaches the gene. What surprised us most was that such a modest reduction in overall transcript level-about 40% in whole leaves-could have such a dramatic effect on trichome density. We think BcCPR5 is expressed specifically in trichome cells, so the actual suppression there is much stronger than what whole‑leaf measurements suggest."

The 3,365‑bp insertion was found in 27.6% of low‑density wucai inbred lines and 36.7% of glabrous pakchoi accessions, but absent from all high‑density lines, suggesting it has been selected during domestication and breeding. The study's findings offer a clear molecular target for breeding wucai varieties with optimized trichome density-balancing the need for pest resistance against consumer preferences for smooth, easy‑to‑harvest leaves. The BcWRKY44‑ BcCPR5 module also provides a conserved framework for understanding trichome regulation across Brassica crops. Looking forward, the team plans to use metabolomics to explore whether high‑density trichomes contribute to nutritional quality, as seen in tea plants where trichomes accumulate valuable flavor compounds.