Petunia pH

A mutation in a gene that helps regulate the acidity of vacuoles gives blue petunias their signature color.

Jan 5, 2014
Abby Olena

FLICKR, BUDDYSAULThough blue petunias are beautiful, until now scientists did not understand how their color arose. Researchers have shown that the PH1 gene encodes protein that works with a proton pump to hyperacidify vacuoles in petal cells and create the typical violet or red color. When PH1 is mutated, vacuoles are less acidic, which results in blue petals. Their work was published in Cell Reports last week (January 2).

“Already in the 1910s it was proposed that blue flower colors were caused by reduced acidity of the ‘cell sap.’ Others figured that drastic changes in the cell sap might cause terrible deleterious defects, and proposed that blue flower colors had something to do with the formation of metal-anthocyanin complexes,” coauthor Francesca Quattrocchio of VU University Amsterdam in the Netherlands said in a statement. “Our current opinion is that both got it right.”

Quattrocchio and colleagues showed that the PH1 gene encodes a P3B-ATPase—a group of Mg2+ transporters only previously shown in bacteria. Though the PH1 protein cannot pump protons, the researchers showed that it can interact directly with PH5—a known proton pump—and boost the pumping activity of PH5. When the team overexpressed PH1 and PH5 together in petunias that were discolored from the loss of function of PH3—another proton pump—it found that PH1 and PH5 were sufficient to restore the petals to their typical color. The researchers also showed directly that petal color and pH were affected by vacuolar acidity in PH mutants.

“By studying the difference between blue and red flowers of petunias, we have discovered a novel type of transporter able to strongly acidify the inside of the vacuole,” Quattrocchio said in the statement.