Gene-Specific Changes in α-Tubulin Transcript Accumulation in Developing Cotton Fibers

Abstract

The fibers of cotton (Gossypium hirsutum) are single-cell trichomes that undergo rapid and synchronous elongation. Cortical microtubules provide spatial information necessary for the alignment of cellulose microfibrils that confine and regulate cell elongation. We used gene-specific probes to investigate ␣-tubulin transcript levels in elongating cotton fibers. Two discrete patterns of transcript accumulation were observed. Whereas transcripts of ␣-tubulin genes GhTua2/3 and GhTua4 increased in abundance from 10 to 20 d post anthesis (DPA), GhTua1 and GhTua5 transcripts were abundant only through to 14 DPA, and dropped significantly at 16 DPA with the onset of secondary wall synthesis. This is the first report, to our knowledge, of gene-specific changes in tubulin transcript levels during the development of a terminally differentiated plant cell. The decrease in abundance of GhTua1 and GhTua5 transcripts was correlated with pronounced changes in cell wall structure, suggesting that ␣-tubulin isoforms may be functionally distinct in elongating fiber cells. Although total ␣-tubulin transcript levels were much higher in fiber than several other tissues, including the hypocotyl and pollen, none of the ␣-tubulins was specific to fiber cells.

Isolation of genes preferentially expressed in cotton fibers by cDNA filter arrays and RT-PCR

“…Based on the sequence comparison, GhTUA6 reported here is different from the previously cloned five a-tubulins, with the highest identity of nucleotide sequence with GhTUA4 . Combined with the expression pattern of various GhTUA members, our results also support the notion that there is a large family of cytoskeleton proteins such as tubulins and actins expressed in fibers and their accumulation is temporally regulated [38]. These unique phenomena may reflect the diverse roles of these different isoforms of microtubule components in rapid cell elongation and dramatic cortical microtubules changes in developing cotton fibers.…”

“…Nine a-tubulin and seven -tubulin isoforms were detected in developing cotton fibers by immunoblot analysis and some genes had a tissue-specific and developmental-regulated expression pattern [37]. It was further reported that five of these distinct a-tubulins showed gene-specific differences in transcript accumulation [38]. Based on the sequence comparison, GhTUA6 reported here is different from the previously cloned five a-tubulins, with the highest identity of nucleotide sequence with GhTUA4 .…”

Differential Expansion and Expression ofα- andβ-Tubulin Gene Families inPopulus

“…Rice (Oryza sativa) also contains a pollen-specific isoform (OryzaTUB8) and seven other TUBs that show variable expression during development (Yoshikawa et al, 2003). Strict temporal association of specific tubulin transcripts during cotton (Gossypium hirsutum) fiber development (Whittaker and Triplett, 1999;Li et al, 2002) or Zinnia tracheary element differentiation (Yoshimura et al, 1996) is consistent with the idea of a functional link between MTs and microfibril deposition during secondary wall synthesis. The five characterized TUAs of cotton are highly expressed in elongating fibers, but only GoshiTUA2/3 and GoshiTUA4 remain abundant following the onset of secondary cell wall synthesis (Whittaker and Triplett, 1999).…”

“…Strict temporal association of specific tubulin transcripts during cotton (Gossypium hirsutum) fiber development (Whittaker and Triplett, 1999;Li et al, 2002) or Zinnia tracheary element differentiation (Yoshimura et al, 1996) is consistent with the idea of a functional link between MTs and microfibril deposition during secondary wall synthesis. The five characterized TUAs of cotton are highly expressed in elongating fibers, but only GoshiTUA2/3 and GoshiTUA4 remain abundant following the onset of secondary cell wall synthesis (Whittaker and Triplett, 1999). In Zinnia, transcripts of ZinelTUB1 and ZinelTUB3 increase during trans-differentiation of mesophyll cells into tracheary elements, contrasting with the constitutive and weak expression of ZinelTUB2 throughout the culture period (Yoshimura et al, 1996).…”

Parallel Domestication, Convergent Evolution and Duplicated Gene Recruitment in Allopolyploid Cotton

“…Some of these genes show changes in total expression as well (Generic probes; Figure 4, A-C). The actin, b-5-tubulin, and villin genes (the first is changed in G. hirsutum and the other two in G. barbadense), for example, are part of the microtubule and cytoskeleton formation system, a process important to plant cell elongation in general and cotton fiber elongation in particular (Whittaker and Triplett 1999;Taliercio and Boykin 2007;Xiang et al 2007;Hovav et al 2008c). The b-d-galactosidase gene, important for primary cell-wall synthesis, has been described as predominantly expressed in fiber cells and tightly associated with fiber elongation (Zhao et al 2001;Hovav et al 2008c).…”