Yellow barley xan-m mutants are deficient in the motor unit SECA1 of the SEC1 translocase system.

Summary: Imagine a barley plant that is born yellow and can never turn green. Scientists investigated a collection of these "mystery" plants, known as xan-m mutants, which were originally discovered between 1925 and 1957. These seedlings sprout with a bright yellow color but die after only about 10 days.

The researchers discovered the cause: a broken gene called xan-m. This gene is responsible for building a specific protein motor called SECA1. In healthy plants, SECA1 acts like a delivery truck, moving essential proteins inside the plant's solar panels (chloroplasts) so they can produce green chlorophyll. Because the mutants lack this motor, they cannot make chlorophyll. However, the study revealed a fascinating twist: the plants can still produce carotenoids (yellow/orange pigments), suggesting that these pigments don't rely on the SECA1 delivery truck. This discovery helps explain the complex logistics of how plants build their energy factories.