Towards elucidating the differential regulation of floral and extrafloral nectar secretion

CRISPR/Cas9-mediated mutagenesis of WRKY3 and WRKY4 function decreases salt and Me-JA stress tolerance in Arabidopsis thaliana

BACKGROUND

WRKY transcription factor is involved in regulation of plant growth and development, response to biotic and abiotic stresses, including homologous WRKY3 and WRKY4 genes which play a vital role in regulating plants defense response to pathogen and drought stress.

METHODS AND RESULTS

To investigate the function of AtWRKY3 and AtWRKY4 genes in regulating salt and Me-JA stresses, the loss-of-function mutations were generated by clustered regularly interspaced short palindromic repeat (CRISPR)/CRISPR-associated 9 (Cas9) system in Arabidopsis thaliana. Several independent transgenic lines with single or double mutations were obtained via Agrobacterium-mediated transformation. The knockout lines of AtWRKY3 and AtWRKY4 genes were successfully achieved and confirmed by qRT-PCR technology. Expression analysis showed that AtWRKY3 and AtWRKY4 genes had significantly up-regulated under salt and Me-JA stresses. The growth of double mutant plants under salt or Me-JA stresses were significantly inhibited compared with corresponding wild type (WT) plants, especially their root lengths. Moreover, the double mutant plants displayed salt and Me-JA sensitivity phenotypic characteristics, such as the increased relative electrolyte leakage (REL) and a substantial reduce in the activities of antioxidant enzymes, including superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) activities.

CONCLUSION

Taken together, these data suggested that the simultaneous modification of homologous gene copies of WRKY are established using CRISPR/Cas9 system in A. thaliana and the loss of AtWRKY3 and AtWRKY4 has an effect on ROS scavenging pathways to reduce stress tolerance.

The Genetic Control of Nectary Development

Nectar is the most important reward offered by flowering plants to pollinators for pollination services. Since pollinator decline has emerged as a major threat for agriculture, and the food demand is growing globally, studying the nectar gland is of utmost importance. Although the genetic mechanisms that control the development of angiosperm flowers have been quite well understood for many years, the development and maturation of the nectar gland and the secretion of nectar in synchrony with the maturation of the sexual organs appears to be one of the flower's best-kept secrets. Here we review key findings controlling these processes. We also raise key questions that need to be addressed to develop crop ecological functions that take into consideration pollinators' needs.

Three's a Crowd: Trade-Offs between Attracting Pollinators and Ant Bodyguards with Nectar Rewards in Turnera

Many plants attract insect pollinators with floral nectar (FN) and ant "bodyguards" with extrafloral nectar (EFN). If nectar production is costly or physiologically linked across glands, investment in one mutualism may trade off with investment in the other. We confirmed that changes in FN and EFN availability alter pollination and ant defense mutualisms in a field population of Turnera ulmifolia. Plants with additional FN tended to produce more seeds, while plants with reduced EFN production experienced less florivory. We then mimicked the consumptive effects of mutualists by removing FN or EFN daily for 50 days in a full factorial design using three Turnera species (T. joelii, T. subulata, and T. ulmifolia) in a glasshouse experiment. For T. ulmifolia and T. subulata, but not T. joelii, removing either nectar reduced production of the other, showing for the first time that EFN and FN production can trade off. In T. subulata, increased investment in FN decreased seed set, suggesting that nectar production can have direct fitness costs. Through the linked expression of EFN and FN, floral visitors may negatively affect biotic defense, and extrafloral nectary visitors may negatively affect pollination.