Comparative transcriptome analysis reveals the candidate genes involved in SDR unreduced female gamete formation in the diploid rubber tree (Hevea brasiliensis (Willd. ex A. Juss.) Mull. Arg.)

Studying the genetic mechanism of 2n gametogenesis is of great significance for understanding and utilizing 2n gametes. We previously found that the rubber clone GT1 could spontaneously and steadily produce second division restitution (SDR) 2n female gametes, indicating that the occurrence of 2n female gametes resulted from gene mutation. Furthermore, low temperature during flower development increased the frequency of 2n female gametes. To identify the genes and reveal the molecular mechanism of SDR-type unreduced female gamete formation in diploid rubber tree, six genes related to SDR 2n gametogenesis were identified by comparing the transcriptomes of female flowers with a high frequency of 2n gametes and female flowers with a low frequency of 2n gametes. A total of 1709 differentially expressed genes were detected in female flowers under cold conditions, with 872 and 837 genes up-regulated and down-regulated, respectively. Six genes, including APC/C, NACK1, NACK2, NPK1, ANP1, and RBR, which are known to be related to SDR-type 2n gametogenesis, were identified and verified by quantitative real-time PCR. Gene function annotation indicated six genes involved in three cytological mechanisms and four corresponding genetic mechanisms of SDR-type 2n gametogenesis. These results suggest that the 2n female gametogenesis process of the rubber tree clone GT1 involves multiple molecular genetic mechanisms, which may differ from model plants such as Arabidopsis and tobacco. Our study provides a basis for identifying the functional genes of natural 2n female gametogenesis, as well as a molecular perspective for revealing the genetic mechanism of the spontaneous production of unreduced female gametes in rubber trees.

Automated summary

By comparing the transcriptomes of female flowers with high and low frequencies of 2n gametes, six genes related to SDR 2n gametogenesis were identified and verified. A total of 1709 differentially expressed genes were detected in female flowers under cold conditions. The study suggests that the 2n female gametogenesis process in rubber tree clone GT1 involves multiple molecular genetic mechanisms.