Cotton fibers are initiated from the epidermal cells of the ovule before or on the day of anthesis. Gossypium arboreum SMA-4 mutant contains recessive mutation (sma-4(ha)) and has the phenotypes of fibreless seeds and glabrous stems. In this study, fine mapping and alternative splicing analysis indicated a nucleotide substitution (AG → AC) at splicing site in a homeodomain-leucine zipper IV family gene (GaHD1) might cause gene A3S (Alternative 3′ splicing) mistake, suggested that GaHD1 was the candidate gene of sma-4(ha). Many genes related to the fiber initiation are identified to be differentially expressed in the mutant which could result in the blocked fiber initiation signals such as H₂O_2, or Ca in the mutant. Further comparative physiological analysis of H₂O₂ production and Ca²⁺ flux in the SMA-4 and wide type cotton confirmed that H₂O₂ and Ca were important fiber initiation signals and regulated by GaHD1. The in vitro ovule culture of the mutant with hormones recovered the fibered phenotype coupled with the restoration of these signals. Overexpressing of GaHD1 in Arabidopsis increased trichome densities on the sepal, leaf, and stem tissues while transient silencing of the GaHD1 gene in G. arboreum reduced the trichome densities. These phenotypes indicated that GaHD1 is the candidate gene of SMA-4 with a crucial role in acting upstream molecular switch of signal transductions for cotton trichome and fiber initiations.

棉花纤维在开花前或开花当天从胚珠的表皮细胞开始。棉桃SMA-4突变体包含隐性突变（sma-4（ha）），并具有无纤维种子和无毛茎的表型。在这项研究中，精细定位和替代剪接分析表明，同源域-亮氨酸拉链IV家族基因（GaHD1）的剪接位点处的核苷酸取代（AG→AC ）可能导致基因A3S（替代3'剪接）错误，提示GaHD1是sma-4（ha）的候选基因。鉴定到许多与纤维起始相关的基因在突变体中差异表达，这可能导致纤维起始信号受阻，例如H ₂O ₂或突变体中的Ca。SMA-4和宽幅棉中H ₂ O ₂产生和Ca ²⁺通量的进一步比较生理分析证实，H ₂ O ₂和Ca是重要的纤维起始信号，并受GaHD1调节。用激素对突变体进行体外胚珠培养可恢复纤维表型，并恢复这些信号。GaHD1在拟南芥中的过表达增加了萼片，叶片和茎组织中毛状体的密度，同时暂时沉默了G. Arboreum中的GaHD1基因。降低毛线密度。这些表型表明，GaHD1是SMA-4的候选基因，在棉花毛状体和纤维萌发的信号转导的上游分子开关中起着关键作用。