LcTRB1, a telomere repeat binding protein, enhances litchi seed development under low temperature by triggering the transcription of LcASHR1

Abstract

The seed development is a crucial step in ensuring a healthy fruit set, and the ultimate seed size is a significant quality feature in fruit crops. Litchi seed development is a fascinating process because of its remarkable plasticity. Previous study has indicated that the partial seed abortion phenotype of litchi cv. ‘Guiwei’ is induced by thermo-sensitive sterility and self-sterility. The comprehension of how genetic background and temperature influence the litchi seed development is limited. Here, we target LcASHR1, a putative histone-lysine N-methyltransferase gene, and LcEMF2, an EMBRYONIC FLOWER 2 gene, that were shown to be more highly expressed in the large seed cultivar ‘Huaizhi’ than in the small seed cultivar ‘Guiwei’. In addition, they were found to be enhanced in response to low temperatures, a condition flavoring the seed development of ‘Guiwei’ seeds. Among them, only the knockdown of LcASHR1 in litchi resulted in tiny seeds and a higher level of seed abortion rate. Conversely, overexpression of LcASHR1 in Arabidopsis lines led to the production of larger seeds. Furthermore, LcTRB1, a putative telomere repeats binding protein, was identified as a upstream transact factor of LcASHR1 by binding to the telo-boxes in the promoter. LcTRB1 expression pattern largely corresponded to litchi seed size. Consistent with previous findings on LcASHR1, it has been observed that LcTRB1 positively affects seed development in both litchi and arabidopsis. Overall, our results indicated that LcTRB1 is linked with litchi seed development probably by modulating the expression of LcASHR1.