Department of Applied Plant Science, Graduate School of Agricultural Science, Tohoku University, Aoba-ku, Sendai, Japan.
J Exp Bot. 2012 Mar;63(5):2159-70. doi: 10.1093/jxb/err434. Epub 2012 Jan 5.
Ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco) small subunit (RBCS) is encoded by a nuclear RBCS multigene family in many plant species. The contribution of the RBCS multigenes to accumulation of Rubisco holoenzyme and photosynthetic characteristics remains unclear. T-DNA insertion mutants of RBCS1A (rbcs1a-1) and RBCS3B (rbcs3b-1) were isolated among the four Arabidopsis RBCS genes, and a double mutant (rbcs1a3b-1) was generated. RBCS1A mRNA was not detected in rbcs1a-1 and rbcs1a3b-1, while the RBCS3B mRNA level was suppressed to ∼20% of the wild-type level in rbcs3b-1 and rbcs1a3b-1 leaves. As a result, total RBCS mRNA levels declined to 52, 79, and 23% of the wild-type level in rbcs1a-1, rbcs3b-1, and rbcs1a3b-1, respectively. Rubisco contents showed declines similar to total RBCS mRNA levels, and the ratio of Rubisco-nitrogen to total nitrogen was 62, 78, and 40% of the wild-type level in rbcs1a-1, rbcs3b-1, and rbcs1a3b-1, respectively. The effects of RBCS1A and RBCS3B mutations in rbcs1a3b-1 were clearly additive. The rates of CO(2) assimilation at ambient CO(2) of 40 Pa were reduced with decreased Rubisco contents in the respective mutant leaves. Although the RBCS composition in the Rubisco holoenzyme changed, the CO(2) assimilation rates per unit of Rubisco content were the same irrespective of the genotype. These results clearly indicate that RBCS1A and RBCS3B contribute to accumulation of Rubisco in Arabidopsis leaves and that these genes work additively to yield sufficient Rubisco for photosynthetic capacity. It is also suggested that the RBCS composition in the Rubisco holoenzyme does not affect photosynthesis under the present ambient [CO(2)] conditions.
核酮糖 1,5-二磷酸羧化酶/加氧酶（Rubisco）小亚基（RBCS）由许多植物物种的核 RBCS 多基因家族编码。RBCS 多基因对 Rubisco 全酶的积累和光合作用特性的贡献尚不清楚。在拟南芥的四个 RBCS 基因中，分离到 RBCS1A（rbcs1a-1）和 RBCS3B（rbcs3b-1）的 T-DNA 插入突变体，并生成了双突变体（rbcs1a3b-1）。rbcs1a-1 和 rbc1a3b-1 中检测不到 RBCS1A mRNA，而 rbcs3b-1 和 rbc1a3b-1 中 RBCS3B mRNA 水平被抑制到野生型水平的约 20%。结果，rbcs1a-1、rbcs3b-1 和 rbc1a3b-1 中的总 RBCS mRNA 水平分别下降到野生型水平的 52%、79%和 23%。Rubisco 含量的下降与总 RBCS mRNA 水平相似，rbcs1a-1、rbcs3b-1 和 rbc1a3b-1 中 Rubisco-氮与总氮的比值分别为野生型水平的 62%、78%和 40%。RBCS1A 和 RBCS3B 突变在 rbc1a3b-1 中的影响明显是累加的。在环境 CO2 为 40 Pa 时，由于突变体叶片中 Rubisco 含量降低，CO2 同化速率降低。尽管 Rubisco 全酶中的 RBCS 组成发生了变化，但单位 Rubisco 含量的 CO2 同化速率与基因型无关。这些结果清楚地表明，RBCS1A 和 RBCS3B 有助于拟南芥叶片中 Rubisco 的积累，这些基因协同作用产生足够的 Rubisco 以满足光合作用能力。这也表明，在当前的环境 CO2 条件下，Rubisco 全酶中的 RBCS 组成不会影响光合作用。
