Recently, the team of Professor Jiang Liquan from the State Key Laboratory of Forest Tree Genetics and Breeding of the School of Forestry at NEFU, published a research paper entitled “Reciprocal cross-regulation of VND and SND multigene TF families for wood formation in Populus trichocarpa” in the top academic journal--"Proceedings of the National Academy of Sciences of the United States of America (PNAS, Comprehensive Journals zone1, IF = 10.414). The first author of the paper is associate professor Lin Yingzhong of the team, and the other participants include seven members of the key laboratory.

The study found that the major regulators of secondary cell wall development in woody plants, PtrVND6-C1 and PtrSND1-A2, have a splice variant, PtrVND6-C1IR and PtrSND1-A2IR, respectively, which can interact as negative regulators regulating the expression of PtrSND1 and PtrVND6 family members. This finding clarifies the new mechanism by which splice variants participate in the regulation of wood formation, laying the newest theoretical basis for the genetic improvement of trees.

Wood is the product of the secondary growth of woody plants and is an important renewable resource that can be used for industrial production and energy output. Secondary cell wall is an important part of wood. A series of important transcription factors are involved in the regulation of secondary cell wall formation. According to research, Vascular-Related NAC Domain (VND) and Secondary Wall-Associated NAC Domain (SND) are key transcription factors involved in the regulation of secondary cell wall formation. Our team reported in 2012 that PtrSND1-A2IR, the PtrSND1-A2 splicing variant, as a negative regulator, inhibited the expression of all PtrSND1 family members except PtrSND1-A2 itself at the PNAS (http://www.pnas.org/content/109/36/14699.short).  Therefore, we speculated that there might be an unknown mechanism to regulate the expression of PtrSND1-A2. In this study, a follow-up study about the report in 2012 was conducted, and PtrVND6-C1IR, a functionally similar splice variant of PtrVND6-C1, was found in PTRVND6-C1 which is a member of NAC transcription factor family. PtrVND6-C1IR inhibited all members of PtrVND6 family except PtrVND6-C1. In addition, we also found that both PtrVND6-C1IR and PtrSND1-A2IR can interact as negative regulators to regulate the expression of PtrSND1 and PtrVND6 members. That is, PtrVND6-C1IR can suppress all PtrSND1 members including PtrSND1-A2 while inhibiting PtrVND6 family members; similarly, PtrSND1-A2IR can suppress all VND members including PtrVND6-C1. The above experimental results show that during the development of forest trees, there is a new mechanism by which the splicing variants of PtrVND6 and PtrSND1 family members regulate the expression of PtrSND1 and PtrVND6 family members. This new mechanism may exist as a common phenomenon in the NAC family of transcription factors as well as other families of transcription factors and elucidate potential new functions of splice variants.

This study has been supported by the National Natural Science Foundation of China Nature Fund project.