Specifically Enhanced Expression Of Auxin Synthetic Gene Affected The Formation Of Adventitious Root In Poplar

Formation of adventitious root is the essential step for cottage.The ability to rapidly produce numerous adventitious roots is important for survival and growth of the seedlings.The mechanisms underlying formation of adventitious root in forest trees is unclear.Previous studies showed that different types of cell within and surrounding vascular tissues can originate adventitious roots.Auxin plays important roles in this process.In this study,we drive the auxin biosynthesis gene PtYUCCA4 under the cambium zone specific promoter LMX5,and studied the mechanisms of adventitious root formation in the pLMX5:PtYUCCA4 transgenic line.As a result,compared with that of control,the growth and development of the aboveground tissues in pLMX5:PtYUCCA4 transgenic line did not show obvious changes.However,the root developed much better in the transgenic seedlings.Further analysis showed that adventitious roots formed faster in transgenic lines.qRT-PCR revealed higher expression levels of PtYUCCA4 in transgenic lines,indicating that the phenotypes were caused by elevated Pt YUCCA4 expression.To study the cause of the accelerated adventitious root formation,we observed the transverse structure of different internodes.We found that the structure of phloem and xylem did not changed obviously.However,the width and cell layer number were increased in the transgenic lines,suggesting that spatially enhanced expression of auxin-biosynthesis genes promoted division of cells with proliferation component.Transcriptomic analysis revealed that 4968 genes were differentially expressed during adventitious root formation in both transgenic and control lines.Of them,genes related to metabolism process,transferase activity,oxidoreductase activity,and those encoding membrane-localized proteins were enriched.The expression levels of 1445 genes were specifically changed in transgenic lines,including a number of genes involved in cell division.Further analysis indicates that the expression levels of jasmonate-synthesis genes were lower in transgenic lines compared with that of control.Genes encode negative regulators of jasmonate signaling were increased during adventitious root formation.Moreover,the expression levels of ethylene synthesis-related genes were preferentially expressed in transgenic lines and were elevated during adventitious root formation.The results show that spatially enhanced auxin biosynthesis in the cambium zone changed signaling of different hormones and promoted cell division,which might be the cause of accelerated adventitious root formation.The results provide new information for understanding the mechanisms of adventitious root formation in forest trees.