The Arabidopsis repressor of light signaling SPA1 acts in the phloem to regulate seedling de-etiolation, leaf expansion and flowering time
The Arabidopsis repressor of light signaling SPA1 acts in the phloem to regulate seedling de-etiolation, leaf expansion and flowering time
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DOI：
10.1242/dev.061036
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发表时间：
2011-05-01
期刊：
影响因子：
4.6
通讯作者：
Hoecker, Ute
中科院分区：
文献类型：
--
作者：
Ranjan, Aashish;Fiene, Gabriele;Hoecker, Ute
植物根据周围的光环境调节其生长发育。这些光反应涉及协调不同组织和器官分化的系统信号。在spa突变背景下，我们通过在组织特异性启动子的控制下表达GUS-SPA1，研究了光形态发生关键抑制因子SPA1在植物不同组织中的功能。我们发现SPA1在韧皮部脉管系统中的表达足以挽救暗生长spa突变苗的SPA1突变表型。相比之下，SPA1在幼苗叶肉、表皮和根组织中的表达没有或只有轻微的影响。在叶片中，SPA1在韧皮部和叶肉中的表达是充分弥补叶片扩张缺陷所必需的。韧皮部和叶肉组织中的SPA1影响表皮层细胞的分裂和扩张，表明SPA1在叶片中也引起非细胞自主反应。光周期开花完全受韧皮部中SPA1的表达控制，这与先前的研究结果一致，表明COP1/SPA复合物的直接底物CONSTANS也在韧皮部中起作用。综上所述，我们的结果突出了韧皮部维管组织在协调生长和发育中的重要性。由于SPA1蛋白本身不能从一个细胞移动到另一个细胞，我们认为SPA1调节光信号下游组分的活性，这些组分随后以非细胞自主的方式起作用。SPA1在韧皮部的作用也可能导致机械刺激，影响其他组织的细胞伸长和细胞分裂。
Plants adjust their growth and development in response to the ambient light environment. These light responses involve systemic signals that coordinate differentiation of different tissues and organs. Here, we have investigated the function of the key repressor of photomorphogenesis SPA1 in different tissues of the plant by expressing GUS-SPA1 under the control of tissue-specific promoters in a spa mutant background. We show that SPA1 expression in the phloem vasculature is sufficient to rescue the spa1 mutant phenotype in dark-grown spa mutant seedlings. Expression of SPA1 in mesophyll, epidermis or root tissues of the seedling, by contrast, has no or only slight effects. In the leaf, SPA1 expression in both the phloem and the mesophyll is required for full complementation of the defect in leaf expansion. SPA1 in phloem and mesophyll tissues affected division and expansion of cells in the epidermal layer, indicating that SPA1 induces non-cell-autonomous responses also in the leaf. Photoperiodic flowering is exclusively controlled by SPA1 expression in the phloem, which is consistent with previous results showing that the direct substrate of the COP1/SPA complex, CONSTANS, also acts in the phloem. Taken together, our results highlight the importance of phloem vascular tissue in coordinating growth and development. Because the SPA1 protein itself is incapable of moving from cell to cell, we suggest that SPA1 regulates the activity of downstream component(s) of light signaling that subsequently act in a non-cell-autonomous manner. SPA1 action in the phloem may also result in mechanical stimuli that affect cell elongation and cell division in other tissues.