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Mentha species are planted worldwide for extraction of their metabolites, including essential oils and phenolic acid compounds, which have therapeutic and commercial value. Mentha piperita L. and Mentha canadensis L. both belong to the menthol chemotype. M. piperita is widely used in North America, and M. canadensis is one of the most important mint species in Asia. Here, an improved Agrobacterium-mediated transformation method using internode segments instead of leaves as explants of M. piperita was reported. Histological examination showed that adventitious buds formed from cortical cells of internode. An efficient method for regeneration of M. canadensis was also established. Internode pieces were excised and cultured on a regeneration medium containing Murashige and Skoog (MS) salts plus vitamin B5, 5.0 mg L−1 TDZ, 0.2 mg L−1 IAA, and 25% coconut water. Explants were then moved to the basal MS medium without plant growth regulator after initiation of shoots and regeneration rates achieved 100%. According to different selection markers used in individual transformation experiments, 3 mg L−1 hygromycin B (antibiotic) or bialaphos (herbicide) was appropriate the concentration for the regeneration selection stage, while 5 mg L−1 hygromycin B or bialaphos could be used during the shoot elongation selection stage. An Agrobacterium-mediated genetic transformation protocol for M. canadensis was produced within 4 mo. Positive transgenic lines with gusA gene were verified by polymerase chain reaction (PCR) and β-glucuronidase histochemical staining. Using 500 to 600 internode pieces as explants could obtain 3 to 4 transgenic lines of M. canadensis. Our methods established here will facilitate the basic gene function research as well as genetic breeding and trait improvement of this important mint species. [ABSTRACT FROM AUTHOR]

The timing of the India‐Asia collision onset, essential to understanding the evolution of the Himalayan‐Tibetan orogen, has been widely investigated through multidisciplinary approaches. Among these, the India to Asia provenance reversal (IAPR) documented in the Indian passive margin successions has proved to be most effective. We present integrated stratigraphic, sedimentological, and provenance data on Upper Cretaceous‐Paleogene strata from the newly investigated Mubala section exposed south of the Yarlung‐Zangbo suture zone (YZSZ) in southern Tibet, which preserves continuous deep‐marine turbiditic and biogenic sedimentation on the distal Indian passive margin. Sandstone petrography, heavy minerals, detrital zircon geochronology and Hf isotopes, and detrital Cr‐spinel geochemistry constrain the IAPR to later than 62.7 Ma (youngest zircon ages from the earliest Asian‐derived sandstone) and by 61.0 ± 0.3 Ma (SIMS age of a tuffaceous layer ∼30 m above this bed). The onset of intercontinental collision along the YZSZ began by 61 Ma. Plain Language Summary: The India‐Asia collision, ultimately leading to uplift of the Himalayan Mountains and Tibetan Plateau, has greatly influenced global climate and oceanic circulation. The timing of collision is essential to reconstruct the growth history of the Himalayan‐Tibetan orogen and its environmental and paleogeographic effects. The change in sediment provenance documented along the Indian continental margin has proved to be a most effective method to constrain the timing of initial collision. We here report a newly‐discovered sedimentary succession deposited onto the deep‐marine edge of India, in which strata composed of detritus derived entirely from India are overlain by strata composed of detritus derived instead from Asia. This provenance change took place later than 62.7 million years ago (Ma; which is the age of the youngest group of zircons contained in the oldest sandstone derived from Asia) and 61.0 ± 0.3 Ma (which is the age of zircon crystals contained in a volcanic tuff found 30 m above the oldest Asian‐derived sandstone). The Indian and Asian continents thus first came into direct contact by 61 Ma. Key Points: Sandstones derived first from India and next from Asia constrain India‐Asia collision onsetThe India‐Asia provenance reversal is bracketed between 62.7 and 61 Ma in the Mubala sectionSubduction of the Indian continental margin beneath Asia began by 61 Ma [ABSTRACT FROM AUTHOR]