A new member of the (+)-δ-cadinene synthase (CAD1) family was isolated from a Gossypium arboreum cDNA library. This cDNA encodes a protein that showed 97.3%, 96.9%, and 79.2% sequence identities with the proteins encoded by previously isolated cDNAs of cad1-C1, cad1-C14, and cad1-A, respectively. It may be grouped into the cad1-C subfamily as cad1-C2. Seeds of a glanded cotton cultivar, G. hirsutum cv. Sumian-6, were collected at different intervals during maturation, and the cad1 mRNA levels were analyzed by quantitative RT-PCR. The transcripts could be detected in seeds of 27 DPA (days postanthesis) and increased dramatically along with the seed maturation, which coordinated with an increase in sesquiterpene cyclase activities and subsequently the accumulation of gossypol. The transcription level detected with primers specific to cad1-C (including at least C1, C14, and cdn1) was higher than that detected with primers specific to cad1-A, and mRNA was detected also with cad1-C2-specific primers. This investigation indicates that, in developing seeds of the glanded cotton cultivar, genes of both the CAD1-C and CAD1-A subfamilies are expressed and there is an active biosynthesis of cadinene-type sesquiterpenes.Plant defense mechanisms involve the induced expression of a complex assortment of genes, including those coding for enzymes catalyzing the formation of antimicrobial secondary metabolites (phytoalexins). In cotton [Gossypium hirsutum L. and Gossypium arboreum L. (Malvaceae)], the production of cadinene-type sesquiterpenes was induced clearly in plants inoculated with the phytopathogenic bacterium Xanthomonas campestris 1,2 and in cell suspension cultures treated with elicitors prepared from the wilt disease-causing fungus Verticillium dahliae. 3 However, cotton sesquiterpenes, including the phenolic aldehyde gossypol, also are constitutive components present in subepidermal pigment glands. 4,5 The occurrence of pigment glands is a distinctive character in the tribe Gossypieae of the family Malvaceae. 4 The glands are found throughout the plant, and they are particularly dense in cotyledons of mature seeds of most cotton cultivars, and high levels of sesquiterpenes (mainly gossypol) are accumulated and deposited in seed glands. 6,7 Sesquiterpene cyclase catalyzes the cyclization of linear farnesyl diphosphate (FPP), the first step committed to the formation of various cyclic sesquiterpenes. [8][9][10] Previous investigations have characterized three cDNAs of the cotton sesquiterpene cyclase, (+)-δ-cadinene synthase (CAD1), from G. arboreum. On the basis of sequence similarities, they were grouped into two subfamilies, cad1-C (including C1 and C14) and cad1-A. 11,12 A cDNA from G. hirsutum, cdn1, which is over 95% identical to G. arboreum cad1-C1 and cad1-C14, has been isolated recently. 13 In addition, the enzyme was purified from bacterial-inoculated G. hirsutum folia tissues. 14 In G. arboreum cell suspension cultures, mRNA levels of both cad1-C and cad1-A subfamilies were increased by 10 times at 6-10 h p...