New Research Makes Populus no Longer “Snow”

Populus is widely distributed all over the world and is one of the main tree species used for afforestation. However, popular catkins cause environmental pollution and seriously restrict the development of the poplar industry. 

On 18 November 2020, the populus team of Nanjing Forestry University published a new paper “Evidences for a role of two Y-specific genes in sex determination in Populus deltoides” in Nature Communication. This study provides an original achievement for the cultivation of a new species of Populus deltoides with no catkins and little pollen.

The populus research group of Nanjing Forestry University did long-term dynamic observation on the female and male flower buds of Populus deltoids and made localization of its sex-determining genes. Y chromosome-specific DNA fragments were found in its sex-determining region, confirming that the sex-determining system of the Populus deltoides, like that of humans, belongs to XY sex-determining system. At the same time, genome-wide association analysis suggested that the differential sequences consistent with gender phenotypes were all derived from Y chromosome- specific fragments.

The fragment contains two genes. FERR-R gene is one of the genes that is a copy formed by the FERR gene that is expressed in female flowers specifically. The cloned FERR-R gene loses part of the sequence, siRNA produced by gene transcription attacks FERR in turn, methylates FERR gene promoter and first exon and degrades FERR transcribed sequence. That inhibits the expression of FERR gene in the male. Another gene MSL on the Y chromosome-specific fragment is the sequence of LTR/Gypsy transposon, which can produce long non-coding RNA.

The study of Arabidopsis thaliana showed that FERR transgenic lines had normal androecium development, but often showed stigma exaggeration, in extreme cases producing flowers with two pistils or carpel-like sepals. However, the overexpression of PdeMSL in A. thaliana did not affect the pistils, and seed set was unaffected, but did affect the androecium, commonly resulting in flowers with six long stamens, or seven or occasionally 8 stamens, stamens bearing two anthers, or branched stamens (Fig. 1), versus the four long and two short stamens of wild-type A. thaliana flowers. These androecium-specific effects suggest that the MSL gene may promote maleness in P. deltoides.