DataSheet_1_Transcriptional regulation of the raffinose family oligosaccharides pathway in Sorghum bicolor reveals potential roles in leaf sucrose transport and stem sucrose accumulation.docx

Bioenergy sorghum hybrids are being developed with enhanced drought tolerance and high levels of stem sugars. Raffinose family oligosaccharides (RFOs) contribute to plant environmental stress tolerance, sugar storage, transport, and signaling. To better understand the role of RFOs in sorghum, genes involved in myo-inositol and RFO metabolism were identified and relative transcript abundance analyzed during development. Genes involved in RFO biosynthesis (SbMIPS1, SbInsPase, SbGolS1, SbRS) were more highly expressed in leaves compared to stems and roots, with peak expression early in the morning in leaves. SbGolS, SbRS, SbAGA1 and SbAGA2 were also expressed at high levels in the leaf collar and leaf sheath. In leaf blades, genes involved in myo-inositol biosynthesis (SbMIPS1, SbInsPase) were expressed in bundle sheath cells, whereas genes involved in galactinol and raffinose synthesis (SbGolS1, SbRS) were expressed in mesophyll cells. Furthermore, SbAGA1 and SbAGA2, genes that encode neutral-alkaline alpha-galactosidases that hydrolyze raffinose, were differentially expressed in minor vein bundle sheath cells and major vein and mid-rib vascular and xylem parenchyma. This suggests that raffinose synthesized from sucrose and galactinol in mesophyll cells diffuses into vascular bundles where hydrolysis releases sucrose for long distance phloem transport. Increased expression (>20-fold) of SbAGA1 and SbAGA2 in stem storage pith parenchyma of sweet sorghum between floral initiation and grain maturity, and higher expression in sweet sorghum compared to grain sorghum, indicates these genes may play a key role in non-structural carbohydrate accumulation in stems.

生物能源高粱杂交品种正在被培育，以增强其耐旱性和茎糖的高含量。 raffinose家族寡糖（RFOs）对植物对环境胁迫的耐受性、糖的储存、运输和信号传导起到重要作用。为了更好地理解RFOs在高粱中的作用，研究人员鉴定了参与肌醇和RFO代谢的基因，并分析了其在发育过程中的相对转录丰度。参与RFO生物合成的基因（SbMIPS1、SbInsPase、SbGolS1、SbRS）在叶片中的表达量高于茎和根，且在清晨叶片中的表达达到峰值。SbGolS、SbRS、SbAGA1和SbAGA2也在叶颈和叶鞘中以高水平表达。在叶片叶片中，参与肌醇生物合成的基因（SbMIPS1、SbInsPase）在维管束鞘细胞中表达，而参与半乳糖醇和 raffinose 合成的基因（SbGolS1、SbRS）在中肋细胞中表达。此外，编码能够水解 raffinose 的中性碱性α-半乳糖苷酶的基因 SbAGA1 和 SbAGA2 在小脉束鞘细胞和主脉及中肋的木质部和韧皮部细胞中呈现差异表达。这表明由中肋细胞中的蔗糖和半乳糖醇合成的 raffinose 可以扩散到维管束中，水解后释放蔗糖，以利于长距离的韧皮部运输。在甜高粱的茎储藏木质部细胞中，SbAGA1 和 SbAGA2 的表达量在花蕾形成到籽粒成熟期间增加了超过20倍，并且与普通高粱相比，甜高粱中这些基因的表达量更高，这表明这些基因可能在茎中非结构性碳水化合物的积累中扮演关键角色。