Moleculer cloning and expression profiling of GhBIL4s, four homologues of Brz-insensitive-long hypocotyls 4 (AtBIL4) in upland cotton (Gossypium hirsutum L.)

Functional Genomics

poster

Fang, Li; Yunlan, Zhai; Ting, Wei; Shue, Ye; Yingcai, Tang; Zhifeng, Zeng; Ming, Luo

Fang, Li

Ming, Luo

Plant steroid hormones, brassinosteroids (BRs) regulate plant growth and development and play an important role in the development of cotton fiber. However, the BR signaling pathway in cotton fiber cell is largely unknown. AtBIL4 (Brz-insensitive-long hypocotyls 4, NM_116196) is a critical component of plant cell elongation occurring upon BR signaling. Considering that cell elongation was a main process in fiber growth, a homologous gene of AtBIL4 was cloned from upland cotton (Gossypium hirsutum L.) and its expression pattern was analyzed in fiber growth. Four BIL4-like genes, designed GhBIL4-1, GhBIL4-2, GhBIL4-3 and GhBIL4-4 were isolated from 10-DPA fiber cells. The amino acids deduced from the ORF of the genes were 243, 248, 248 and 248, respectively. Four GhBIL4 proteins were membrane proteins and seven transmembrane domains were in each sequence. BLAST searches of GhBIL4s amino acid sequence identified similar genes in Arabidopsis, poplar, grape, bean, tomato, potato, and rice. Interestingly, the GhBIL4s have high homology with BI, a Bax Inhibitor involved in programmed cell death. Overexpressing BI in plant could improve the tolerance to cell death induced by biotic or abiotic stress. GhBIL4s expressed widely in all detected samples although different expression level present in various tissues, organs, and cells. The highest levels of GhBIL4-1 transcript were in fiber cells. Moderate and similar expression levels were observed in root, stem, leaf, hypocotyl, pollen, and ovule. The expression peak of GhBIL4-3 was in fiber cells while identical expression in the other samples. Either GhBIL4-2 or GhBIL4-4 expressed highly in stem, hypocotyl, fiber cell, and ovule. The lowest expression level was detected in pollen. Therefore, GhBIL4s expressed preferentially in fiber cells. In the various developmental stages of fibers, four genes expressed slightly in 0~4 DPA ovules (with fibers) and highly expressed in fiber cells. GhBIL4-1 and GhBIL4-3 shared a similar expression pattern in the growth of fiber cells. Identical and moderate levels present in the fibers of 6~10 DPA while the highest levels was displayed in the fibers of 14~20 DPA. The expression levels of GhBIL4-2 and GhBIL4-4 were elevated drastically in 6 DPA fiber cells compared to 4 DPA ovules. Consequently, the expression decreased slightly and sustained high expression level in 8~20 DPA fiber. These results suggested that the GhBIL4s might play important roles in the growth and development of fiber, especially in fiber elongation and secondary cell wall deposition. Furthermore, GhBIL4s might be involved in the resistance to biotic or abiotic stress induced by BRs. Using a vector provided kindly by professor Nakano Takeshi (RIKEN), we have obtained transgenic cotton lines overexpressed AtBIL4. The terminal bud development of transgenic plants was suppressed and the reproductive development was retarded. The flower bud abolished and the pollen was sterility in transgenic plants. So that cotton bolls were hardly harvested. These results further indicated that GhBIL4s play important roles in the growth and development of cotton plant. Keywords: upland cotton; brassinosteroids(BRs); GhBIL4;