Comparative transcriptome analyses reveal insights into catkin bloom patterns in pecan protogynous and protandrous cultivars

Abstract

In perennial plants such as pecan, once reproductive maturity is attained, there are genetic switches that are regulated and required for flower development year after year. Pecan trees are heterodichogamous with both pistillate and staminate flowers produced on the same tree. Therefore, defining genes exclusively responsible for pistillate inflorescence and staminate inflorescence (catkin) initiation is challenging at best. To understand these genetic switches and their timing, this study analyzed catkin bloom and gene expression of lateral buds collected from a protogynous (Wichita) and a protandrous (Western) pecan cultivar in summer, autumn and spring. Our data showed that pistillate flowers in the current season on the same shoot negatively impacted catkin production on the protogynous ‘Wichita’ cultivar. Whereas fruit production the previous year on ‘Wichita’ had a positive effect on catkin production on the same shoot the following year. However, fruiting the previous year nor current year pistillate flower production had no significant effect on catkin production on ‘Western’ (protandrous cultivar) cultivar. The RNA-Seq results present more significant differences between the fruiting and non-fruiting shoots of the ‘Wichita’ cultivar compared to the ‘Western’ cultivar, revealing the genetic signals likely responsible for catkin production. Our data presented here, indicates the genes showing expression for the initiation of both types of flowers the season before bloom.

Distinct ancient structural polymorphisms control heterodichogamy in walnuts and hickories

“…However, applying the McDonald-Kreitman test to each gene, the ratio of nonsynonymous to synonymous substitutions vs. polymorphisms did not identify any signals of adaptive evolution. We note however that two of these genes with annotated functional roles in flowering, EMS1 and FIL1 , were previously identified in a small set of highly differentially expressed genes between male catkin buds of protandrous and protogynous cultivars in the season prior to bloom near when a differential in anther development is first established (Rhein et al . 2023).…”