Anthocyanin composition and expression analysis of anthocyanin biosynthetic genes in kidney bean pod

Kidney bean (Phaseolus vulgaris L.) is an important dietary legume crop cultivated and consumed worldwide. A purple cultivar (Zi Bawang) and a green cultivar (Chun Qiu), the main difference of which is in the pod skin color, were selected for the study. Malvidin 3, 5-diglucoside is identified as the major anthocyanin in the pod skin of Zi Bawang by HPLC-ESI-MS/MS. Three regulatory genes PvMYB1, PvMYB2, PvTT8-1 and most structural genes are dramatically up-regulated in purple pod skin compared to those in other materials. Significantly decreased expression levels of all regulatory genes and most biosynthetic genes are also detected in the purple skin of pods covered with bags compared to non-covered ones. All the results suggest that PvMYB1, PvMYB2 and PvTT8-1 might play a critical role in transcriptional activation of most anthocyanin biosynthetic genes in purple kidney bean pod.