Arabidopsis WRKY1 promotes monocarpic senescence by integrative regulation of flowering,leaf senescence,and nitrogen remobilization

Monocarpic senescence,characterized by whole-plant senescence following a single flowering phase,is widespread in seed plants,particularly in crops,determining seed harvest time and quality.However,how external and internal signals are systemically integrated into monocarpic senescence remains largely unknown.Here,we report that the Arabidopsis thaliana transcription factor WRKY1 plays essential roles in multiple key steps of monocarpic senescence.WRKY1 expression is induced by age,salicylic acid(SA),and nitrogen(N)deficiency.Flowering and leaf senescence are accelerated in the WRKY1 overexpression lines but are delayed in the wrky1 mutants.The combined DNA affinity purification sequencing and RNA sequencing analyses uncover the direct target genes of WRKY1.Further studies show that WRKY1 coordinately regulates three processes in monocarpic senescence:(1)suppressing FLOWERING LOCUS C gene expression to initiate flowering,(2)inducing SA biosynthesis genes to promote leaf senescence,and(3)activating the N assimilation and transport genes to trigger N remobilization.In summary,our study reveals how one stress-responsive transcription factor,WRKY1,integrates flowering,leaf senescence,and N remobilization processes into monocarpic senescence,providing important insights into plant lifetime regulation.

Foliar applications of various nitrogen(N)forms to winter wheat affect grain protein accumulation and quality via N metabolism and remobilization

Foliar nitrogen(N)application is an effective strategy to improve protein content and quality in wheat kernels,but the specific effects of N forms remain unclear.In a two-year field study,foliar application of various N forms(NO_(3)^(-),urea,NH_(4)^(+))at anthesis was performed to measure their effects on wheat grain protein accumulation,quality formation,and the underlying mechanisms.Foliar application of three N forms showed varying effects in improving grain gluten proteins and quality traits.Under NH_(4)^(+) application,there was more post-anthesis N uptake for grain filling,with relatively strong increase in enzyme activities and gene expression associated with N metabolism in flag leaves at 8–20 days after anthesis(DAA),whereas its promotion of grain N metabolism became weaker after 20 DAA than those under NO_(3)^(-) and urea treatments.More N was remobilized from source organs to grain under treatment with foliar NO_(3)^(-) and urea.Genes controlling the synthesis of gluten protein and disulfide bonds were upregulated by NO_(3)^(-) and urea at 20–28 DAA,contributing to increased grain protein content and quality.Overall,foliar applications of NO_(3)^(-) and urea were more effective than those of NH_(4)^(+) in increasing grain N filling.These findings show that manipulating the source–sink relationship by reinforcing grain N metabolism and N remobilization is critical for optimizing grain protein accumulation and quality formation.

Effect of Source-Sink Manipulation on Photosynthetic Characteristics of Flag Leaf and the Remobilization of Dry Mass and Nitrogen in Vegetative Organs of Wheat

The photosynthetic characteristics of flag leaf and the accumulation and remobilization of pre-anthesis dry mass（DM） and nitrogen（N） in vegetable organs in nine wheat cultivars under different source-sink manipulation treatments including defoliation（DF）, spike shading（SS） and half spikelets removal（SR） were investigated. Results showed that the SS treatment increased the photosynthetic rate（Pn） of flag leaf in source limited cultivar, but had no significant effect on sink limited cultivar. The SR treatment decreased the Pn of flag leaf. Grain DM accumulation was limited by source in some cultivars, in other cultivars, it was limited by sink. Grain N accumulation was mainly limited by source supply. The contribution of pre-anthesis dry mass to grain yield from high to low was stem, leaf and chaff, while the contribution of pre-anthesis N to grain N from high to low was leaf, stem and chaff. Cultivars S7221 and TA9818 can increase the contribution of remobilization of DM and N to grain at the maximum ratio under reducing source treatments, which may be the major reason for these cultivars having lower decrease in grain yield and N content under reducing source treatments.

Micro-sprinkling irrigation simultaneously improves grain yield and protein concentration of winter wheat in the North China Plain

Increased grain yield(GY) and grain protein concentration(GPC) are the two main targets of efforts to improve wheat(Triticum aestivum L.) production in the North China Plain(NCP). We conducted a three-year field experiment in the 2014–2017 winter wheat growing seasons to compare the effects of conventional irrigation practice(CI) and micro-sprinkling irrigation combined with nitrogen(N) fertilizer(MSI) on GY, GPC, and protein yield(PY). Across the three years, GY, GPC, and PY increased by 10.5%–16.7%, 5.4%–8.0%, and 18.8%–24.6%, respectively, under MSI relative to CI. The higher GY under MSI was due primarily to increased thousand-kernel weight(TKW). The chlorophyll content of leaves was higher under MSI during the mid–late grain filling period, increasing the contribution of post-anthesis dry matter accumulation to GY, with consequent increases in total dry matter accumulation and harvest index compared to CI. During the mid–late grain filling period, the canopy temperature was markedly lower and the relative humidity was higher under MSI than under CI. The duration and rate of filling during the mid–late grain filling period were also higher under MSI than CI, resulting in higher TKW. MSI increased the contribution of post-anthesis N accumulation to grain N but reduced the pre-anthesis remobilization of N in leaves, the primary site of photosynthetic activity, possibly helping maintain photosynthate production in leaves during grain filling. Total N at maturity was higher under MSI than CI,although there was little difference in N harvest index. The higher GPC under MSI than under CI was due to a larger increase in grain N accumulation than in GY. Overall, MSI simultaneously increased both GY and GPC in winter wheat grown in the NCP.