Using DNA sequencing, a team of researchers have figured out how the citrus greening bacterium affects trees even before symptoms appear.

Anhaya Dandekar, a University of California, Davis, plant scientist, led the study that found the disease interferes with starch and sugar metabolism in young and mature leaves and fruit.

At the same time, the bacterial disease disrupts hormonal networks that play key roles in trees' ability to fend off infections.

This new-found knowledge can be used to help develop diagnostic tests and treatments for citrus greening, also known as huanglongbing or HLB, according to a news release.

As part of their study, the researchers examined four categories of healthy and diseased trees.

Earlier work had shown with the bacterial genome showed it didn't produce toxins or enzymes that might destroy plant cell walls.

"Because these factors, which normally accompany plant diseases, were not present, we suspected that the disease was causing metabolic imbalances or interfering with nutrient transport in the infected trees," Dandekar said in the release.

The researchers used gene sequencing technology to study RNA found in tree leaves and fruit.

Their analysis confirmed that HLB causes starch to accumulate in the leaves of infected plants, blocking nutrient transport through the phloem and decreasing photosynthesis.

They also found that normal metabolism of sucrose, a sugar key to photosynthesis, was disrupted.

In addition, they discovered that HLB interferes with the regulation of hormones, such as salicylic acid, jasmonic acid and ethylene, which are the backbone of plant immune responses.

Other researchers in the study were Federico Martinelli, Russell Reagan, Sandra Uratsu and My Phu, all of the UC Davis Department of Plant Sciences; Ute Albrecht and Kim Bowman, both of the U.S. Department of Agriculture Agricultural Research Service, Fort Pierce, Fla.; and Weixian Zhao and Cristina Davis, both of the UC Davis Department of Mechanical and Aerospace Engineering.