Efficient Evergreen Plant Regeneration of Cinnamomum japonicum Sieb.through in vitro Organogenesis

Cinnamomum japonicum Sieb.is an excellent roadside tree and medicinal tree species with considerable ornamental and economic value.In this study,we successfully developed a large-scale micropropagation protocol for C.japonicum for the first time.Sterilized shoots were excised and used as explants for shoot induction on several basal media,supplemented with different concentrations of plant growth regulators(PGRs),such as Thidiazuron(TDZ),N^(6)-Benzyladenine(6-benzylaminopurine)(BA),α-naphthaleneacetic acid(NAA)and Gibberellic acid(GA_(3)).After comparison,the most efficient medium for shoot regeneration was 1/2 Murashige and Skoog(MS)medium containing 0.5 mg L^(-1)BA,0.05 mg L^(-1)NAA and 0.2 mg L^(-1)GA_(3),which resulted in an average number of induced shoots per explant and shoot length of 5.2 and 1.62 cm at 28 d,respectively.Then,elongated adventitious shoots were transferred to induce roots.86.7%of shoots was able to root on 1/2 MS medium supplemented with 0.5 mg L^(-1)NAA and 0.1 mg L^(-1)BA.The earliest rooting time observed was after 21 d and the average root length was up to 3.3 cm after 28 d.Our study shows that C.japonicum can be successfully regenerated through de novo organogenesis,which lays a foundation for future transformation research on this tree.

TAA family contributes to auxin production during de novo regeneration of adventitious roots from Arabidopsis leaf explants

Many differentiated plant organs have the ability to regenerate into a new plant after detachment via de novo organogenesis. During de novo root organogenesis from Arabidopsis thaliana leaf explants, wounding first induces endogenous auxin production in mesophyll cells. Auxin is then polar transported to, and accumulates in, regenerationcompetent cells near the wound to trigger the cell-fate transition. The TRYPTOPHAN AMINOTRANSFERASE OF ARABIDOPSIS(TAA) family proteins and the YUCCA(YUC) family proteins catalyze two successive biochemical steps in auxin biogenesis, and YUCs have been shown to be involved in auxin production in mesophyll cells during de novo root organogenesis. In thisstudy, we show that the TAA family is also required for adventitious rooting. Inhibition of TAA blocked adventitious root formation from leaf explants. Intriguingly,whereas YUC1 and YUC4 have been shown to be highly induced by wounding, TAA genes retained consistent expression levels before and after leaf detachment.Therefore, we suggest that TAAs and YUCs are both required for auxin biogenesis in leaf explants, but they play different roles in regeneration. While YUC1 and YUC4 function in response to wounding to catalyze the ratelimiting step in auxin biosynthesis, TAAs probably serve as abiding and basal enzymes during de novo root organogenesis from leaf explants.