Flower-Specific Overproduction of Cytokinins Altered Flower Development and Sex Expression in the Perennial Woody Plant Jatropha curcas L.

Abstract

Jatropha curcas L. is monoecious with a low female-to-male ratio, which is one of the factors restricting its seed yield. Because the phytohormone cytokinins play an essential role in flower development, particularly pistil development, in this study, we elevated the cytokinin levels in J. curcas flowers through transgenic expression of a cytokinin biosynthetic gene (AtIPT4) from Arabidopsis under the control of a J. curcas orthologue of TOMATO MADS BOX GENE 6 (JcTM6) promoter that is predominantly active in flowers. As expected, the levels of six cytokinin species in the inflorescences were elevated, and flower development was modified without any alterations in vegetative growth. In the transgenic J. curcas plants, the flower number per inflorescence was significantly increased, and most flowers were pistil-predominantly bisexual, i.e., the flowers had a huge pistil surrounded with small stamens. Unfortunately, both the male and the bisexual flowers of transgenic J. curcas were infertile, which might have resulted from the continuously high expression of the transgene during flower development. However, the number and position of floral organs in the transgenic flowers were well defined, which suggested that the determinacy of the floral meristem was not affected. These results suggest that fine-tuning the endogenous cytokinins can increase the flower number and the female-to-male ratio in J. curcas.

Silencing of the Ortholog of DEFECTIVE IN ANTHER DEHISCENCE 1 Gene in the Woody Perennial Jatropha curcas Alters Flower and Fruit Development

“…Treatment with exogenous gibberellic acid (GA) was found to increase the number of female flowers in Jatropha [ 53 , 54 , 55 ], similar to the phenotypes of the JcDAD1 -RNAi transgenic plants ( Figure 5 E). Moreover, both exogenous benzyladenine (BA) treatment and flower-specific overproduction of endogenous cytokinins (CKs) promoted the total flower number and female flower number in Jatropha [ 38 , 56 ], which again resembled the phenotypes of the JcDAD1 -RNAi transgenic plants ( Figure 5 E,F). These results indicate that JA may act together with GA and/or CK to regulate flower development in Jatropha .…”

Jatropha curcasortholog oftomato MADS-box gene 6(JcTM6) promoter exhibits floral-specific activity inArabidopsis thaliana

“…This activity is consistent with the expression pattern of the JcTM6 gene in Jatropha. Recently, Ming et al (2020) showed that JcTM6 promoter has a high activity in female flowers of Jatropha, suggesting that JcTM6 promoter can drive flower-specific expression of transgenes in different plant species.…”

Biotechnological Research Progress in Jatropha, a Biodiesel-Yielding Plant

“…They found an increase in the number of flowers in a single inflorescence, but both the male and the bisexual flowers were infertile due to the continuous expression of the transgene. The transformation was performed using A. tumefaciens EHA105 [ 73 ].…”